WebGL Specification

Editor's Draft Wed Sep 18 17:19:10 2024 -0700

This version:: https://www.khronos.org/registry/webgl/specs/latest/1.0/
WebIDL: https://www.khronos.org/registry/webgl/specs/latest/1.0/webgl.idl
Latest version:: https://www.khronos.org/registry/webgl/specs/latest/1.0/
WebIDL: https://www.khronos.org/registry/webgl/specs/latest/1.0/webgl.idl
Previous version:: https://www.khronos.org/registry/webgl/specs/1.0.3/
WebIDL: https://www.khronos.org/registry/webgl/specs/1.0.3/webgl.idl
Editors:: Dean Jackson (Apple Inc.); Jeff Gilbert (Mozilla Corp.)

Abstract

This specification describes an additional rendering context and support objects for the HTML 5 canvas element [CANVAS]. This context allows rendering using an API that conforms closely to the OpenGL ES 2.0 API.

Status of this document

This document is an editor's draft. Do not cite this document as other than work in progress.

Feedback

Public discussion of this specification is welcome on the [email protected] mailing list (instructions, archives).

Please file bugs against the specification or its conformance tests in the issue tracker. Pull requests are welcome against the Github repository.

Introduction

WebGL™ is an immediate mode 3D rendering API designed for the web. It is derived from OpenGL® ES 2.0, and provides similar rendering functionality, but in an HTML context. WebGL is designed as a rendering context for the HTML Canvas element. The HTML Canvas provides a destination for programmatic rendering in web pages, and allows for performing that rendering using different rendering APIs. The only such interface described as part of the Canvas specification is the 2D canvas rendering context, CanvasRenderingContext2D. This document describes another such interface, WebGLRenderingContext, which presents the WebGL API.

The immediate mode nature of the API is a divergence from most web APIs. Given the many use cases of 3D graphics, WebGL chooses the approach of providing flexible primitives that can be applied to any use case. Libraries can provide an API on top of WebGL that is more tailored to specific areas, thus adding a convenience layer to WebGL that can accelerate and simplify development. However, because of its OpenGL ES 2.0 heritage, it should be straightforward for developers familiar with modern desktop OpenGL or OpenGL ES 2.0 development to transition to WebGL development.

Conventions

Many functions described in this document contain links to OpenGL ES man pages. While every effort is made to make these pages match the OpenGL ES 2.0 specification [GLES20], they may contain errors. In the case of a contradiction, the OpenGL ES 2.0 specification is the final authority.

The remaining sections of this document are intended to be read in conjunction with the OpenGL ES 2.0 specification (2.0.25 at the time of this writing, available from the Khronos OpenGL ES API Registry). Unless otherwise specified, the behavior of each method is defined by the OpenGL ES 2.0 specification. This specification may diverge from OpenGL ES 2.0 in order to ensure interoperability or security, often defining areas that OpenGL ES 2.0 leaves implementation-defined. These differences are summarized in the Differences Between WebGL and OpenGL ES 2.0 section.

Context Creation and Drawing Buffer Presentation

Before using the WebGL API, the author must obtain a WebGLRenderingContext object for a given HTMLCanvasElement [CANVAS] or OffscreenCanvas [OFFSCREENCANVAS] as described below. This object is used to manage OpenGL state and render to the drawing buffer, which must be created at the time of context creation.

Context Creation

Each WebGLRenderingContext has an associated canvas, set upon creation, which is a canvas [CANVAS] or offscreen canvas [OFFSCREENCANVAS].

Each WebGLRenderingContext has context creation parameters, set upon creation, in a WebGLContextAttributes object.

Each WebGLRenderingContext has actual context parameters, set each time the drawing buffer is created, in a WebGLContextAttributes object.

Each WebGLRenderingContext has a webgl context lost flag, which is initially unset.

When the getContext() method of a canvas element or offscreen canvas object is to return a new object for the contextId webgl [CANVASCONTEXTS], the user agent must perform the following steps:

Create a new WebGLRenderingContext object, context.
Let context's canvas be the canvas or offscreen canvas the getContext() method is associated with.
Create a new WebGLContextAttributes object, contextAttributes.
If getContext() was invoked with a second argument, options, set the attributes of contextAttributes from those specified in options.
Create a drawing buffer using the settings specified in contextAttributes, and associate the drawing buffer with context.
If drawing buffer creation failed, perform the following steps:
1. Fire a WebGL context creation error at canvas.
2. Return null and terminate these steps.
Create a new WebGLContextAttributes object, actualAttributes.
Set the attributes of actualAttributes based on the properties of the newly created drawing buffer.
Set context's context creation parameters to contextAttributes.
Set context's actual context parameters to actualAttributes.
Return context.

The canvas context type 'experimental-webgl' has historically been used to provide access to WebGL implementations which are not yet complete or conformant.

If the user agent supports both the webgl and experimental-webgl canvas context types, they shall be treated as aliases. For example, if a call to getContext('webgl') successfully creates a WebGLRenderingContext, a subsequent call to getContext('experimental-webgl') shall return the same context object.

The Drawing Buffer

The drawing buffer into which the API calls are rendered shall be defined upon creation of the WebGLRenderingContext object. The following description defines how to create a drawing buffer.

The table below shows all the buffers which make up the drawing buffer, along with their minimum sizes and whether they are defined or not by default. The size of this drawing buffer shall be determined by the width and height attributes of the HTMLCanvasElement or OffscreenCanvas. The table below also shows the value to which these buffers shall be cleared when first created, when the size is changed, or after presentation when the preserveDrawingBuffer context creation attribute is false.

Buffer	Clear value	Minimum size	Defined by default?
Color	(0, 0, 0, 0)	8 bits per component	yes
Depth	1.0	16 bit integer	yes
Stencil	0	8 bits	no

HTMLCanvasElement.width and .height values less than 1 are treated as 1. A 0x0 canvas will yield a 1x1 drawingBufferWidth/Height.

If the requested width or height cannot be satisfied, either when the drawing buffer is first created or when the width and height attributes of the HTMLCanvasElement or OffscreenCanvas are changed, a drawing buffer with smaller dimensions shall be created. The dimensions actually used are implementation dependent and there is no guarantee that a buffer with the same aspect ratio will be created. The actual drawing buffer size can be obtained from the drawingBufferWidth and drawingBufferHeight attributes.

A WebGL implementation must not perform any automatic scaling of the size of the drawing buffer on high-definition displays. The context's drawingBufferWidth and drawingBufferHeight must match the canvas's width and height attributes as closely as possible, modulo implementation-dependent constraints.

The constraint above does not change the amount of space the canvas element consumes on the web page, even on a high-definition display. The canvas's intrinsic dimensions [CANVAS] equal the size of its coordinate space, with the numbers interpreted in CSS pixels, and CSS pixels are resolution-independent [CSS].

A WebGL application can achieve a 1:1 ratio between drawing buffer pixels and on-screen pixels on high-definition displays by examining properties like window.devicePixelRatio, scaling the canvas's width and height by that factor, and setting its CSS width and height to the original width and height. An application can simulate the effect of running on a higher-resolution display simply by scaling up the canvas's width and height properties.

The optional WebGLContextAttributes object may be used to change whether or not the buffers are defined. It can also be used to define whether the color buffer will include an alpha channel. If defined, the alpha channel is used by the HTML compositor to combine the color buffer with the rest of the page. The WebGLContextAttributes object is only used on the first call to getContext. No facility is provided to change the attributes of the drawing buffer after its creation.

The depth, stencil and antialias attributes, when set to true, are requests, not requirements. The WebGL implementation should make a best effort to honor them. When any of these attributes is set to false, however, the WebGL implementation must not provide the associated functionality. Combinations of attributes not supported by the WebGL implementation or graphics hardware shall not cause a failure to create a WebGLRenderingContext. The actual context parameters are set to the attributes of the created drawing buffer. The alpha, premultipliedAlpha and preserveDrawingBuffer attributes must be obeyed by the WebGL implementation.

WebGL presents its drawing buffer to the HTML page compositor immediately before a compositing operation, but only if at least one of the following have been called since the previous compositing operation:

Context creation
Canvas resize
Any of the [Draw Operations], called while the drawing buffer is the currently bound (draw) framebuffer.

Before the drawing buffer is presented for compositing the implementation shall ensure that all rendering operations have been flushed to the drawing buffer. By default, after compositing the contents of the drawing buffer shall be cleared to their default values, as shown in the table above.

This default behavior can be changed by setting the preserveDrawingBuffer attribute of the WebGLContextAttributes object. If this flag is true, the contents of the drawing buffer shall be preserved until the author either clears or overwrites them. If this flag is false, attempting to perform operations using this context as a source image after the rendering function has returned can lead to undefined behavior. This includes readPixels or toDataURL calls, using this context as the source image of another context's texImage2D or drawImage call, or creating an ImageBitmap [HTML] from this context's canvas.

While it is sometimes desirable to preserve the drawing buffer, it can cause significant performance loss on some platforms. Whenever possible this flag should remain false and other techniques used. Techniques like synchronous drawing buffer access (e.g., calling readPixels or toDataURL in the same function that renders to the drawing buffer) can be used to get the contents of the drawing buffer. If the author needs to render to the same drawing buffer over a series of calls, a Framebuffer Object can be used.

Implementations may optimize away the required implicit clear operation of the Drawing Buffer as long as a guarantee can be made that the author cannot gain access to buffer contents from another process. For instance, if the author performs an explicit clear then the implicit clear is not needed.

undefined drawingBufferStorage(GLenum sizedFormat, unsigned long width, unsigned long height);

Respecify the format and size of the drawing buffer, similar to renderbufferStorage as used on Renderbuffers. Clearing behavior is equivalent to setting HTMLCanvasElement.width and HTMLCanvasElement.height, followed by changing the drawing buffer format. This method respects WebGLContextAttributes.antialias.

drawingBufferStorage allows for efficiently respecifying width and height together simultaneously. With HTMLCanvasElement.width and HTMLCanvasElement.height, setting one and then the other can incur intermediate reallocations, though User Agents do try to optimize these out.

If drawingBufferStorage is successful, the drawingBufferFormat becomes sizedFormat. drawingBufferWidth and drawingBufferHeight become width and height respectively. Operations on the default framebuffer therefore behave as if operating on a non-default framebuffer with an attachment of sizedFormat. E.g. after drawingBufferStorage(gl.RGBA16F, 1, 1), because the framebuffer is "floatish", readPixels's main format/type pair is RGBA/FLOAT instead of RGBA/UNSIGNED_BYTE. If WebGLContextAttributes.alpha is false, generate INVALID_OPERATION. RGBA8 is always supported for sizedFormat. Additionally, the following enums are supported if they are currently valid for renderbufferStorage:

RGBA8
SRGB8_ALPHA8 (0x8C43) (E.g. from EXT_sRGB)
RGBA16F (0x881A) (E.g. from EXT_color_buffer_half_float)

If sizedFormat is not currently supported, generate INVALID_ENUM.

In WebGL 1.0, SRGB8_ALPHA8 requires the extension EXT_sRGB. In WebGL 2.0, SRGB8_ALPHA8 does not require an extension.

In WebGL 1.0, RGBA16F requires the extension EXT_color_buffer_half_float. In WebGL 2.0, RGBA16F requires the extension EXT_color_buffer_float.

If width or height are greater than the limit MAX_RENDERBUFFER_SIZE, generate INVALID_VALUE. If allocation fails, generate OUT_OF_MEMORY.

The WebGL Viewport

OpenGL manages a rectangular viewport as part of its state which defines the placement of the rendering results in the drawing buffer. Upon creation of WebGL context context, the viewport is initialized to a rectangle with origin at (0, 0) and width and height equal to (context.drawingBufferWidth, context.drawingBufferHeight).

A WebGL implementation shall not affect the state of the OpenGL viewport in response to resizing of the canvas element.

Note that if a WebGL program does not contain logic to set the viewport, it will not properly handle the case where the canvas is resized. The following ECMAScript example illustrates how a WebGL program might resize the canvas programmatically.

var canvas = document.getElementById('canvas1');
var gl = canvas.getContext('webgl');
canvas.width = newWidth;
canvas.height = newHeight;
gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);

Rationale: automatically setting the viewport will interfere with applications that set it manually. Applications are expected to use onresize handlers to respond to changes in size of the canvas and set the OpenGL viewport in turn.

Premultiplied Alpha, Canvas APIs and texImage2D

The OpenGL API allows the application to modify the blending modes used during rendering, and for this reason allows control over how alpha values in the drawing buffer are interpreted; see the premultipliedAlpha parameter in the WebGLContextAttributes section.

The HTML Canvas APIs toDataURL and drawImage must respect the premultipliedAlpha context creation parameter. When toDataURL is called against a Canvas into which WebGL content is being rendered, then if the requested image format does not specify premultiplied alpha and the WebGL context has the premultipliedAlpha parameter set to true, then the pixel values must be de-multiplied; i.e., the color channels are divided by the alpha channel. Note that this operation is lossy.

Passing a WebGL-rendered Canvas to the drawImage method of CanvasRenderingContext2D may or may not need to modify the the rendered WebGL content during the drawing operation, depending on the premultiplication needs of the CanvasRenderingContext2D implementation.

When passing a WebGL-rendered Canvas to the texImage2D API, then depending on the setting of the premultipliedAlpha context creation parameter of the passed canvas and the UNPACK_PREMULTIPLY_ALPHA_WEBGL pixel store parameter of the destination WebGL context, the pixel data may need to be changed to or from premultiplied form.

WebGL Resources

OpenGL manages several types of resources as part of its state. These are identified by integer object names and are obtained from OpenGL by various creation calls. In contrast WebGL represents these resources as DOM objects. Each object is derived from the WebGLObject interface. Currently supported resources are: textures, buffers (i.e., VBOs), framebuffers, renderbuffers, shaders and programs. The WebGLRenderingContext interface has a method to create a WebGLObject subclass for each type. Data from the underlying graphics library are stored in these objects and are fully managed by them. The DOM object will stay alive not only as long as the author retains an explicit reference to it, but also as long as it is in use by the underlying graphics library. When the DOM object is destroyed, it marks its resources for deletion. If authors wish to mark an object for deletion prior to the DOM object being destroyed, they may explicitly call the respective delete function. (e.g. deleteTexture)

Security

Resource Restrictions

WebGL resources such as textures and vertex buffer objects (VBOs) must always contain initialized data, even if they were created without initial user data values. Creating a resource without initial values is commonly used to reserve space for a texture or VBO, which is then modified using texSubImage or bufferSubData calls. If initial data is not provided to these calls, the WebGL implementation must initialize their contents to 0; depth resources must be cleared to the default 1.0 clear depth. This may require creating a zeroed temporary buffer the size of a requested VBO, so that it can be initialized correctly. All other forms of loading data into a texture or VBO involve either ArrayBuffers or DOM objects such as images, and are therefore already required to be initialized.

When WebGL resources are accessed by shaders through a call such as drawElements or drawArrays, the WebGL implementation must ensure that the shader cannot access either out of bounds or uninitialized data. See Enabled Vertex Attributes and Range Checking for restrictions which must be enforced by the WebGL implementation.

Origin Restrictions

In order to prevent information leakage, WebGL disallows uploading as textures:

Image or video elements whose origin is not the same as the origin of the Document that contains the WebGLRenderingContext's canvas element
Canvas elements whose bitmap's origin-clean flag is set to false
ImageBitmap objects whose bitmap's origin-clean flag is set to false

If the texImage2D or texSubImage2D method is called with otherwise correct arguments and an HTMLImageElement, HTMLVideoElement, HTMLCanvasElement, or ImageBitmap violating these restrictions, a SECURITY_ERR exception must be thrown.

WebGL necessarily imposes stronger restrictions on the use of cross-domain media than other APIs such as the 2D canvas rendering context, because shaders can be used to indirectly deduce the contents of textures which have been uploaded to the GPU.

WebGL applications may utilize images and videos that come from other domains, with the cooperation of the server hosting the media, using Cross-Origin Resource Sharing [CORS]. In order to use such media, the application needs to explicitly request permission to do so, and the server needs to explicitly grant permission. Successful CORS-enabled fetches of image and video elements from other domains cause the origin of these elements to be set to that of the containing Document [HTML].

The following ECMAScript example demonstrates how to issue a CORS request for an image coming from another domain. The image is fetched from the server without any credentials, i.e., cookies.

var gl = ...;
var image = new Image();

// The onload handler should be set to a function which uploads the HTMLImageElement
// using texImage2D or texSubImage2D.
image.onload = ...;

image.crossOrigin = "anonymous";

image.src = "http://other-domain.com/image.jpg";

Note that these rules imply that the origin-clean flag for a canvas rendered using WebGL will never be set to false.

For more information on issuing CORS requests for image and video elements, consult:

Supported GLSL Constructs

A WebGL implementation must only accept shaders which conform to The OpenGL ES Shading Language, Version 1.00 [GLES20GLSL], and which do not exceed the minimum functionality mandated in Sections 4 and 5 of Appendix A. In particular:

A shader referencing state variables or functions that are available in other versions of GLSL, such as that found in versions of OpenGL for the desktop, must not be allowed to load.
for loops must conform to the structural constraints in Appendix A.
while and do-while loops are disallowed, since they are optional in Appendix A.
Appendix A mandates certain forms of indexing of arrays; for example, within fragment shaders, indexing is only mandated with a constant-index-expression (see [GLES20GLSL] for the definition of this term). In the WebGL API, only the forms of indexing mandated in Appendix A are supported.

In addition to the reserved identifiers in the aforementioned specification, identifiers starting with "webgl_" and "_webgl_" are reserved for use by WebGL. A shader which declares a function, variable, structure name, or structure field starting with these prefixes must not be allowed to load.

WebGL 1.0 implementations must additionally support the line continuation character '\' in shaders.

Defense Against Denial of Service

It is possible to create, either intentionally or unintentionally, combinations of shaders and geometry that take an undesirably long time to render. This issue is analogous to that of long-running scripts, for which user agents already have safeguards. However, long-running draw calls can cause loss of interactivity for the entire window system, not just the user agent.

In the general case it is not possible to impose limits on the structure of incoming shaders to guard against this problem. Experimentation has shown that even very strict structural limits are insufficient to prevent long rendering times, and such limits would prevent shader authors from implementing common algorithms.

User agents should implement safeguards to prevent excessively long rendering times and associated loss of interactivity. Suggested safeguards include:

Splitting up draw calls with large numbers of elements into smaller draw calls.
Timing individual draw calls and forbidding further rendering from a page if a certain timeout is exceeded.
Using any watchdog facilities available at the user level, graphics API level, or operating system level to limit the duration of draw calls.
Separating the graphics rendering of the user agent into a distinct operating system process which can be terminated and restarted without losing application state.

The supporting infrastructure at the OS and graphics API layer is expected to improve over time, which is why the exact nature of these safeguards is not specified.

Out-of-Range Array Accesses

Shaders must not be allowed to read or write array elements that lie outside of the application's own data. This includes any variable of array type, as well as vector or matrix types such as vec3 or mat4 when accessed using array subscripting syntax. If detected during compilation, such accesses must generate an error and prevent the shader from compiling. Otherwise, at runtime, out-of-range reads shall return any of the following values:

Values from anywhere within the storage accessible to the program.
Zero values, or (0,0,0,x) vectors for vector reads where x is a valid value represented in the type of the vector components and may be any of:
- 0, 1, or the maximum representable positive integer value, for signed or unsigned integer components
- 0.0 or 1.0, for floating-point components

Out-of-range writes are either discarded or modify an unspecified value in the storage accessible to the program.

This behavior replicates that defined in [KHRROBUSTACCESS].

See Supported GLSL Constructs for more information on restrictions which simplify static analysis of the array indexing operations in shaders.

DOM Interfaces

This section describes the interfaces and functionality added to the DOM to support runtime access to the functionality described above.

Types

The following types are used in all interfaces in the following section.

typedef unsigned long  GLenum;
typedef boolean        GLboolean;
typedef unsigned long  GLbitfield;
typedef byte           GLbyte;         /* 'byte' should be a signed 8 bit type. */
typedef short          GLshort;
typedef long           GLint;
typedef long           GLsizei;
typedef long long      GLintptr;
typedef long long      GLsizeiptr;
// Ideally the typedef below would use 'unsigned byte', but that doesn't currently exist in Web IDL.
typedef octet          GLubyte;        /* 'octet' should be an unsigned 8 bit type. */
typedef unsigned short GLushort;
typedef unsigned long  GLuint;
typedef unrestricted float GLfloat;
typedef unrestricted float GLclampf;

// The power preference settings are documented in the WebGLContextAttributes
// section of the specification.
enum WebGLPowerPreference { "default", "low-power", "high-performance" };

WebGLContextAttributes

The WebGLContextAttributes dictionary contains drawing surface attributes and is passed as the second parameter to getContext.

dictionary WebGLContextAttributes {
    boolean alpha = true;
    boolean depth = true;
    boolean stencil = false;
    boolean antialias = true;
    boolean premultipliedAlpha = true;
    boolean preserveDrawingBuffer = false;
    WebGLPowerPreference powerPreference = "default";
    boolean failIfMajorPerformanceCaveat = false;
    boolean desynchronized = false;
};

Context creation parameters

The following list describes each attribute in the WebGLContextAttributes object and its use. The default value for each attribute is shown above. The default value is used either if no second parameter is passed to getContext, or if a user object is passed which has no attribute of the given name.

alpha

If the value is true, the drawing buffer has an alpha channel for the purposes of performing OpenGL destination alpha operations and compositing with the page. If the value is false, no alpha buffer is available.

depth

If the value is true, the drawing buffer has a depth buffer of at least 16 bits. If the value is false, no depth buffer is available.

stencil

If the value is true, the drawing buffer has a stencil buffer of at least 8 bits. If the value is false, no stencil buffer is available.

antialias

If the value is true and the implementation supports antialiasing the drawing buffer will perform antialiasing using its choice of technique (multisample/supersample) and quality. If the value is false or the implementation does not support antialiasing, no antialiasing is performed.

premultipliedAlpha

If the value is true the page compositor will assume the drawing buffer contains colors with premultiplied alpha. If the value is false the page compositor will assume that colors in the drawing buffer are not premultiplied. This flag is ignored if the alpha flag is false.

With premultipliedAlpha:true, any pixels sent to the page compositor shall have color values less-than-or-equal-to their alpha value, otherwise the colors resulting from compositing such out-of-range pixel values are undefined.

For example, with premultipliedAlpha:true vec4(1.0, 0.0, 0.0, 0.5) might display as green instead of red, possibly due to optimized packed compositing math overflows. This is left undefined due to the intractible performance impact of requiring consistent behavior.

See Premultiplied Alpha for more information on the effects of the premultipliedAlpha flag.

preserveDrawingBuffer

If false, once the drawing buffer is presented as described in theDrawing Buffer section, the contents of the drawing buffer are cleared to their default values. All elements of the drawing buffer (color, depth and stencil) are cleared. If the value is true the buffers will not be cleared and will preserve their values until cleared or overwritten by the author.

On some hardware setting the preserveDrawingBuffer flag to true can have significant performance implications.

powerPreference

Provides a hint to the user agent indicating what configuration of GPU is suitable for this WebGL context. This may influence which GPU is used in a system with multiple GPUs. For example, a dual-GPU system might have one GPU that consumes less power at the expense of rendering performance. Note that this property is only a hint and a WebGL implementation may choose to ignore it.

WebGL implementations use context lost and restored events to regulate power and memory consumption, regardless of the value of this attribute.

The allowed values are:

default

Let the user agent decide which GPU configuration is most suitable. This is the default value.

high-performance

Indicates a request for a GPU configuration that prioritizes rendering performance over power consumption. Developers are encouraged to only specify this value if they believe it is absolutely necessary, since it may significantly decrease battery life on mobile devices. Implementations may decide to initially respect this request and, after some time, lose the context and restore a new context ignoring the request.

Applications that request high-performance should test and maintain robust context loss handling, as User Agents are very likely to decide to lose background high-performance contexts.

low-power

Indicates a request for a GPU configuration that prioritizes power saving over rendering performance. Generally, content should use this if it is unlikely to be constrained by drawing performance; for example, if it renders only one frame per second, draws only relatively simple geometry with simple shaders, or uses a small HTML canvas element. Developers are encouraged to use this value if their content allows, since it may significantly improve battery life on mobile devices.

failIfMajorPerformanceCaveat

If the value is true, context creation will fail if the implementation determines that the performance of the created WebGL context would be dramatically lower than that of a native application making equivalent OpenGL calls. This could happen for a number of reasons, including:

An implementation might switch to a software rasterizer if the user's GPU driver is known to be unstable.
An implementation might require reading back the framebuffer from GPU memory to system memory before compositing it with the rest of the page, significantly reducing performance.

Applications that don't require high performance should leave this parameter at its default value of false. Applications that require high performance may set this parameter to true, and if context creation fails then the application may prefer to use a fallback rendering path such as a 2D canvas context. Alternatively the application can retry WebGL context creation with this parameter set to false, with the knowledge that a reduced-fidelity rendering mode should be used to improve performance.

desynchronized

If the value is true, then the user agent may optimize the rendering of the canvas to reduce the latency, as measured from input events to rasterization, by desynchronizing the canvas paint cycle from the event loop, bypassing the ordinary user agent rendering algorithm, or both. Insofar as this mode involves bypassing the usual paint mechanisms, rasterization, or both, it might introduce visible tearing artifacts.

The user agent usually renders on a buffer which is not being displayed, quickly swapping it and the one being scanned out for presentation; the former buffer is called back buffer and the latter front buffer. A popular technique for reducing latency is called front buffer rendering, also known as single buffer rendering, where rendering happens inparallel and racily with the scanning out process. This technique reduces the latency at the price of potentially introducing tearing artifacts and can be used to implement in total or part of the desynchronized boolean. [MULTIPLEBUFFERING]

The desynchronized boolean can be useful when implementing certain kinds of applications, such as drawing applications, where the latency between input and rasterization is critical.

Here is an ECMAScript example which passes a WebGLContextAttributes argument to getContext. It assumes the presence of a canvas element named "canvas1" on the page.

var canvas = document.getElementById('canvas1');
var context = canvas.getContext('webgl',
                                { antialias: false,
                                  stencil: true });

WebGLObject

The WebGLObject interface is the parent interface for all GL objects.

Each WebGLObject has an internal invalidated flag, which is initially unset.

Each WebGLObject has a .label attribute, which defaults to "". Implementations should use this application-provided label string to improve debugging, e.g. in error messages, and/or providing the label to any underlying driver where possible to assist in native-level debugging tools. Implementations must not change behavior due to a label.

[Exposed=(Window,Worker)]
interface WebGLObject {
    attribute USVString label;
};

WebGLBuffer

The WebGLBuffer interface represents an OpenGL Buffer Object. The underlying object is created as if by calling glGenBuffers (OpenGL ES 2.0 §2.9, man page) , bound as if by calling glBindBuffer (OpenGL ES 2.0 §2.9, man page) and marked for deletion as if by calling glDeleteBuffers (OpenGL ES 2.0 §2.9, man page) .

[Exposed=(Window,Worker)]
interface WebGLBuffer : WebGLObject {
};

WebGLFramebuffer

The WebGLFramebuffer interface represents an OpenGL Framebuffer Object. The underlying object is created as if by calling glGenFramebuffers (OpenGL ES 2.0 §4.4.1, man page) , bound as if by calling glBindFramebuffer (OpenGL ES 2.0 §4.4.1, man page) and marked for deletion as if by calling glDeleteFramebuffers (OpenGL ES 2.0 §4.4.1, man page) .

[Exposed=(Window,Worker)]
interface WebGLFramebuffer : WebGLObject {
};

WebGLProgram

The WebGLProgram interface represents an OpenGL Program Object. The underlying object is created as if by calling glCreateProgram (OpenGL ES 2.0 §2.10.3, man page) , used as if by calling glUseProgram (OpenGL ES 2.0 §2.10.3, man page) and marked for deletion as if by calling glDeleteProgram (OpenGL ES 2.0 §2.10.3, man page) .

[Exposed=(Window,Worker)]
interface WebGLProgram : WebGLObject {
};

WebGLRenderbuffer

The WebGLRenderbuffer interface represents an OpenGL Renderbuffer Object. The underlying object is created as if by calling glGenRenderbuffers (OpenGL ES 2.0 §4.4.3, man page) , bound as if by calling glBindRenderbuffer (OpenGL ES 2.0 §4.4.3, man page) and marked for deletion as if by calling glDeleteRenderbuffers (OpenGL ES 2.0 §4.4.3, man page) .

[Exposed=(Window,Worker)]
interface WebGLRenderbuffer : WebGLObject {
};

WebGLShader

The WebGLShader interface represents an OpenGL Shader Object. The underlying object is created as if by calling glCreateShader (OpenGL ES 2.0 §2.10.1, man page) , attached to a Program as if by calling glAttachShader (OpenGL ES 2.0 §2.10.3, man page) and marked for deletion as if by calling glDeleteShader (OpenGL ES 2.0 §2.10.1, man page) .

[Exposed=(Window,Worker)]
interface WebGLShader : WebGLObject {
};

WebGLTexture

The WebGLTexture interface represents an OpenGL Texture Object. The underlying object is created as if by calling glGenTextures (OpenGL ES 2.0 §3.7.13, man page) , bound as if by calling glBindTexture (OpenGL ES 2.0 §3.7.13, man page) and marked for deletion as if by calling glDeleteTextures (OpenGL ES 2.0 §3.7.13, man page) .

[Exposed=(Window,Worker)]
interface WebGLTexture : WebGLObject {
};

WebGLUniformLocation

The WebGLUniformLocation interface represents the location of a uniform variable in a shader program.

[Exposed=(Window,Worker)]
interface WebGLUniformLocation {
};

WebGLActiveInfo

The WebGLActiveInfo interface represents the information returned from the getActiveAttrib and getActiveUniform calls.

[Exposed=(Window,Worker)]
interface WebGLActiveInfo {
    readonly attribute GLint size;
    readonly attribute GLenum type;
    readonly attribute DOMString name;
};

Attributes

The following attributes are available:

size of type GLint: The size of the requested variable.
type of type GLenum: The data type of the requested variable.
name of type DOMString: The name of the requested variable.

WebGLShaderPrecisionFormat

The WebGLShaderPrecisionFormat interface represents the information returned from the getShaderPrecisionFormat call.

[Exposed=(Window,Worker)]
interface WebGLShaderPrecisionFormat {
    readonly attribute GLint rangeMin;
    readonly attribute GLint rangeMax;
    readonly attribute GLint precision;
};

Attributes

The following attributes are available:

rangeMin of type GLint: The base 2 log of the absolute value of the minimum value that can be represented.
rangeMax of type GLint: The base 2 log of the absolute value of the maximum value that can be represented.
precision of type GLint: The number of bits of precision that can be represented. For integer formats this value is always 0.

ArrayBuffer and Typed Arrays

Vertex, index, texture, and other data is transferred to the WebGL implementation using ArrayBuffers, Typed Arrays and DataViews as defined in the ECMAScript specification [ECMASCRIPT].

Typed Arrays support the creation of interleaved, heterogeneous vertex data; uploading of distinct blocks of data into a large vertex buffer object; and most other use cases required by OpenGL programs.

Here is an ECMAScript example showing access to the same ArrayBuffer using different types of typed arrays. In this case the buffer contains a floating point vertex position (x, y, z) followed by a color as 4 unsigned bytes (r, g, b, a).

var numVertices = 100; // for example

// Compute the size needed for the buffer, in bytes and floats
var vertexSize = 3 * Float32Array.BYTES_PER_ELEMENT +
     4 * Uint8Array.BYTES_PER_ELEMENT;
var vertexSizeInFloats = vertexSize / Float32Array.BYTES_PER_ELEMENT;

// Allocate the buffer
var buf = new ArrayBuffer(numVertices * vertexSize);

// Map this buffer to a Float32Array to access the positions
var positionArray = new Float32Array(buf);

// Map the same buffer to a Uint8Array to access the color
var colorArray = new Uint8Array(buf);

// Set up the initial offset of the vertices and colors within the buffer
var positionIdx = 0;
var colorIdx = 3 * Float32Array.BYTES_PER_ELEMENT;

// Initialize the buffer
for (var i = 0; i < numVertices; i++) {
    positionArray[positionIdx] = ...;
    positionArray[positionIdx + 1] = ...;
    positionArray[positionIdx + 2] = ...;
    colorArray[colorIdx] = ...;
    colorArray[colorIdx + 1] = ...;
    colorArray[colorIdx + 2] = ...;
    colorArray[colorIdx + 3] = ...;
    positionIdx += vertexSizeInFloats;
    colorIdx += vertexSize;
}

The WebGL context

The WebGLRenderingContext represents the API allowing OpenGL ES 2.0 style rendering into the canvas element.

Before performing the implementation of any method of the WebGLRenderingContext interface or any method of an interface returned by the getExtension method, the following steps must be performed:

If the [WebGLHandlesContextLoss] extended attribute appears on the called method, perform the implementation of the called method, return its result and terminate these steps.
Let use default return value be false.
If the webgl context lost flag is set, let use default return value be true.
1. Otherwise, if any argument to the method is a WebGLObject with its invalidated flag set, generate an INVALID_OPERATION error and let use default return value be true.
If use default return value is true, perform the following steps:
1. If the return type of the called method is any or any nullable type, return null.
2. Terminate this algorithm without calling the method implementation.
Otherwise, perform the implementation of the called method and return its result.

See the context lost event for further details.

typedef (ImageBitmap or
         ImageData or
         HTMLImageElement or
         HTMLCanvasElement or
         HTMLVideoElement or
         OffscreenCanvas or
         VideoFrame) TexImageSource;

typedef ([AllowShared] Float32Array or sequence<GLfloat>) Float32List;
typedef ([AllowShared] Int32Array or sequence<GLint>) Int32List;

interface mixin WebGLRenderingContextBase
{

    /* ClearBufferMask */
    const GLenum DEPTH_BUFFER_BIT               = 0x00000100;
    const GLenum STENCIL_BUFFER_BIT             = 0x00000400;
    const GLenum COLOR_BUFFER_BIT               = 0x00004000;

    /* BeginMode */
    const GLenum POINTS                         = 0x0000;
    const GLenum LINES                          = 0x0001;
    const GLenum LINE_LOOP                      = 0x0002;
    const GLenum LINE_STRIP                     = 0x0003;
    const GLenum TRIANGLES                      = 0x0004;
    const GLenum TRIANGLE_STRIP                 = 0x0005;
    const GLenum TRIANGLE_FAN                   = 0x0006;

    /* AlphaFunction (not supported in ES20) */
    /*      NEVER */
    /*      LESS */
    /*      EQUAL */
    /*      LEQUAL */
    /*      GREATER */
    /*      NOTEQUAL */
    /*      GEQUAL */
    /*      ALWAYS */

    /* BlendingFactorDest */
    const GLenum ZERO                           = 0;
    const GLenum ONE                            = 1;
    const GLenum SRC_COLOR                      = 0x0300;
    const GLenum ONE_MINUS_SRC_COLOR            = 0x0301;
    const GLenum SRC_ALPHA                      = 0x0302;
    const GLenum ONE_MINUS_SRC_ALPHA            = 0x0303;
    const GLenum DST_ALPHA                      = 0x0304;
    const GLenum ONE_MINUS_DST_ALPHA            = 0x0305;

    /* BlendingFactorSrc */
    /*      ZERO */
    /*      ONE */
    const GLenum DST_COLOR                      = 0x0306;
    const GLenum ONE_MINUS_DST_COLOR            = 0x0307;
    const GLenum SRC_ALPHA_SATURATE             = 0x0308;
    /*      SRC_ALPHA */
    /*      ONE_MINUS_SRC_ALPHA */
    /*      DST_ALPHA */
    /*      ONE_MINUS_DST_ALPHA */

    /* BlendEquationSeparate */
    const GLenum FUNC_ADD                       = 0x8006;
    const GLenum BLEND_EQUATION                 = 0x8009;
    const GLenum BLEND_EQUATION_RGB             = 0x8009;   /* same as BLEND_EQUATION */
    const GLenum BLEND_EQUATION_ALPHA           = 0x883D;

    /* BlendSubtract */
    const GLenum FUNC_SUBTRACT                  = 0x800A;
    const GLenum FUNC_REVERSE_SUBTRACT          = 0x800B;

    /* Separate Blend Functions */
    const GLenum BLEND_DST_RGB                  = 0x80C8;
    const GLenum BLEND_SRC_RGB                  = 0x80C9;
    const GLenum BLEND_DST_ALPHA                = 0x80CA;
    const GLenum BLEND_SRC_ALPHA                = 0x80CB;
    const GLenum CONSTANT_COLOR                 = 0x8001;
    const GLenum ONE_MINUS_CONSTANT_COLOR       = 0x8002;
    const GLenum CONSTANT_ALPHA                 = 0x8003;
    const GLenum ONE_MINUS_CONSTANT_ALPHA       = 0x8004;
    const GLenum BLEND_COLOR                    = 0x8005;

    /* Buffer Objects */
    const GLenum ARRAY_BUFFER                   = 0x8892;
    const GLenum ELEMENT_ARRAY_BUFFER           = 0x8893;
    const GLenum ARRAY_BUFFER_BINDING           = 0x8894;
    const GLenum ELEMENT_ARRAY_BUFFER_BINDING   = 0x8895;

    const GLenum STREAM_DRAW                    = 0x88E0;
    const GLenum STATIC_DRAW                    = 0x88E4;
    const GLenum DYNAMIC_DRAW                   = 0x88E8;

    const GLenum BUFFER_SIZE                    = 0x8764;
    const GLenum BUFFER_USAGE                   = 0x8765;

    const GLenum CURRENT_VERTEX_ATTRIB          = 0x8626;

    /* CullFaceMode */
    const GLenum FRONT                          = 0x0404;
    const GLenum BACK                           = 0x0405;
    const GLenum FRONT_AND_BACK                 = 0x0408;

    /* DepthFunction */
    /*      NEVER */
    /*      LESS */
    /*      EQUAL */
    /*      LEQUAL */
    /*      GREATER */
    /*      NOTEQUAL */
    /*      GEQUAL */
    /*      ALWAYS */

    /* EnableCap */
    /* TEXTURE_2D */
    const GLenum CULL_FACE                      = 0x0B44;
    const GLenum BLEND                          = 0x0BE2;
    const GLenum DITHER                         = 0x0BD0;
    const GLenum STENCIL_TEST                   = 0x0B90;
    const GLenum DEPTH_TEST                     = 0x0B71;
    const GLenum SCISSOR_TEST                   = 0x0C11;
    const GLenum POLYGON_OFFSET_FILL            = 0x8037;
    const GLenum SAMPLE_ALPHA_TO_COVERAGE       = 0x809E;
    const GLenum SAMPLE_COVERAGE                = 0x80A0;

    /* ErrorCode */
    const GLenum NO_ERROR                       = 0;
    const GLenum INVALID_ENUM                   = 0x0500;
    const GLenum INVALID_VALUE                  = 0x0501;
    const GLenum INVALID_OPERATION              = 0x0502;
    const GLenum OUT_OF_MEMORY                  = 0x0505;

    /* FrontFaceDirection */
    const GLenum CW                             = 0x0900;
    const GLenum CCW                            = 0x0901;

    /* GetPName */
    const GLenum LINE_WIDTH                     = 0x0B21;
    const GLenum ALIASED_POINT_SIZE_RANGE       = 0x846D;
    const GLenum ALIASED_LINE_WIDTH_RANGE       = 0x846E;
    const GLenum CULL_FACE_MODE                 = 0x0B45;
    const GLenum FRONT_FACE                     = 0x0B46;
    const GLenum DEPTH_RANGE                    = 0x0B70;
    const GLenum DEPTH_WRITEMASK                = 0x0B72;
    const GLenum DEPTH_CLEAR_VALUE              = 0x0B73;
    const GLenum DEPTH_FUNC                     = 0x0B74;
    const GLenum STENCIL_CLEAR_VALUE            = 0x0B91;
    const GLenum STENCIL_FUNC                   = 0x0B92;
    const GLenum STENCIL_FAIL                   = 0x0B94;
    const GLenum STENCIL_PASS_DEPTH_FAIL        = 0x0B95;
    const GLenum STENCIL_PASS_DEPTH_PASS        = 0x0B96;
    const GLenum STENCIL_REF                    = 0x0B97;
    const GLenum STENCIL_VALUE_MASK             = 0x0B93;
    const GLenum STENCIL_WRITEMASK              = 0x0B98;
    const GLenum STENCIL_BACK_FUNC              = 0x8800;
    const GLenum STENCIL_BACK_FAIL              = 0x8801;
    const GLenum STENCIL_BACK_PASS_DEPTH_FAIL   = 0x8802;
    const GLenum STENCIL_BACK_PASS_DEPTH_PASS   = 0x8803;
    const GLenum STENCIL_BACK_REF               = 0x8CA3;
    const GLenum STENCIL_BACK_VALUE_MASK        = 0x8CA4;
    const GLenum STENCIL_BACK_WRITEMASK         = 0x8CA5;
    const GLenum VIEWPORT                       = 0x0BA2;
    const GLenum SCISSOR_BOX                    = 0x0C10;
    /*      SCISSOR_TEST */
    const GLenum COLOR_CLEAR_VALUE              = 0x0C22;
    const GLenum COLOR_WRITEMASK                = 0x0C23;
    const GLenum UNPACK_ALIGNMENT               = 0x0CF5;
    const GLenum PACK_ALIGNMENT                 = 0x0D05;
    const GLenum MAX_TEXTURE_SIZE               = 0x0D33;
    const GLenum MAX_VIEWPORT_DIMS              = 0x0D3A;
    const GLenum SUBPIXEL_BITS                  = 0x0D50;
    const GLenum RED_BITS                       = 0x0D52;
    const GLenum GREEN_BITS                     = 0x0D53;
    const GLenum BLUE_BITS                      = 0x0D54;
    const GLenum ALPHA_BITS                     = 0x0D55;
    const GLenum DEPTH_BITS                     = 0x0D56;
    const GLenum STENCIL_BITS                   = 0x0D57;
    const GLenum POLYGON_OFFSET_UNITS           = 0x2A00;
    /*      POLYGON_OFFSET_FILL */
    const GLenum POLYGON_OFFSET_FACTOR          = 0x8038;
    const GLenum TEXTURE_BINDING_2D             = 0x8069;
    const GLenum SAMPLE_BUFFERS                 = 0x80A8;
    const GLenum SAMPLES                        = 0x80A9;
    const GLenum SAMPLE_COVERAGE_VALUE          = 0x80AA;
    const GLenum SAMPLE_COVERAGE_INVERT         = 0x80AB;

    /* GetTextureParameter */
    /*      TEXTURE_MAG_FILTER */
    /*      TEXTURE_MIN_FILTER */
    /*      TEXTURE_WRAP_S */
    /*      TEXTURE_WRAP_T */

    const GLenum COMPRESSED_TEXTURE_FORMATS     = 0x86A3;

    /* HintMode */
    const GLenum DONT_CARE                      = 0x1100;
    const GLenum FASTEST                        = 0x1101;
    const GLenum NICEST                         = 0x1102;

    /* HintTarget */
    const GLenum GENERATE_MIPMAP_HINT            = 0x8192;

    /* DataType */
    const GLenum BYTE                           = 0x1400;
    const GLenum UNSIGNED_BYTE                  = 0x1401;
    const GLenum SHORT                          = 0x1402;
    const GLenum UNSIGNED_SHORT                 = 0x1403;
    const GLenum INT                            = 0x1404;
    const GLenum UNSIGNED_INT                   = 0x1405;
    const GLenum FLOAT                          = 0x1406;

    /* PixelFormat */
    const GLenum DEPTH_COMPONENT                = 0x1902;
    const GLenum ALPHA                          = 0x1906;
    const GLenum RGB                            = 0x1907;
    const GLenum RGBA                           = 0x1908;
    const GLenum LUMINANCE                      = 0x1909;
    const GLenum LUMINANCE_ALPHA                = 0x190A;

    /* PixelType */
    /*      UNSIGNED_BYTE */
    const GLenum UNSIGNED_SHORT_4_4_4_4         = 0x8033;
    const GLenum UNSIGNED_SHORT_5_5_5_1         = 0x8034;
    const GLenum UNSIGNED_SHORT_5_6_5           = 0x8363;

    /* Shaders */
    const GLenum FRAGMENT_SHADER                  = 0x8B30;
    const GLenum VERTEX_SHADER                    = 0x8B31;
    const GLenum MAX_VERTEX_ATTRIBS               = 0x8869;
    const GLenum MAX_VERTEX_UNIFORM_VECTORS       = 0x8DFB;
    const GLenum MAX_VARYING_VECTORS              = 0x8DFC;
    const GLenum MAX_COMBINED_TEXTURE_IMAGE_UNITS = 0x8B4D;
    const GLenum MAX_VERTEX_TEXTURE_IMAGE_UNITS   = 0x8B4C;
    const GLenum MAX_TEXTURE_IMAGE_UNITS          = 0x8872;
    const GLenum MAX_FRAGMENT_UNIFORM_VECTORS     = 0x8DFD;
    const GLenum SHADER_TYPE                      = 0x8B4F;
    const GLenum DELETE_STATUS                    = 0x8B80;
    const GLenum LINK_STATUS                      = 0x8B82;
    const GLenum VALIDATE_STATUS                  = 0x8B83;
    const GLenum ATTACHED_SHADERS                 = 0x8B85;
    const GLenum ACTIVE_UNIFORMS                  = 0x8B86;
    const GLenum ACTIVE_ATTRIBUTES                = 0x8B89;
    const GLenum SHADING_LANGUAGE_VERSION         = 0x8B8C;
    const GLenum CURRENT_PROGRAM                  = 0x8B8D;

    /* StencilFunction */
    const GLenum NEVER                          = 0x0200;
    const GLenum LESS                           = 0x0201;
    const GLenum EQUAL                          = 0x0202;
    const GLenum LEQUAL                         = 0x0203;
    const GLenum GREATER                        = 0x0204;
    const GLenum NOTEQUAL                       = 0x0205;
    const GLenum GEQUAL                         = 0x0206;
    const GLenum ALWAYS                         = 0x0207;

    /* StencilOp */
    /*      ZERO */
    const GLenum KEEP                           = 0x1E00;
    const GLenum REPLACE                        = 0x1E01;
    const GLenum INCR                           = 0x1E02;
    const GLenum DECR                           = 0x1E03;
    const GLenum INVERT                         = 0x150A;
    const GLenum INCR_WRAP                      = 0x8507;
    const GLenum DECR_WRAP                      = 0x8508;

    /* StringName */
    const GLenum VENDOR                         = 0x1F00;
    const GLenum RENDERER                       = 0x1F01;
    const GLenum VERSION                        = 0x1F02;

    /* TextureMagFilter */
    const GLenum NEAREST                        = 0x2600;
    const GLenum LINEAR                         = 0x2601;

    /* TextureMinFilter */
    /*      NEAREST */
    /*      LINEAR */
    const GLenum NEAREST_MIPMAP_NEAREST         = 0x2700;
    const GLenum LINEAR_MIPMAP_NEAREST          = 0x2701;
    const GLenum NEAREST_MIPMAP_LINEAR          = 0x2702;
    const GLenum LINEAR_MIPMAP_LINEAR           = 0x2703;

    /* TextureParameterName */
    const GLenum TEXTURE_MAG_FILTER             = 0x2800;
    const GLenum TEXTURE_MIN_FILTER             = 0x2801;
    const GLenum TEXTURE_WRAP_S                 = 0x2802;
    const GLenum TEXTURE_WRAP_T                 = 0x2803;

    /* TextureTarget */
    const GLenum TEXTURE_2D                     = 0x0DE1;
    const GLenum TEXTURE                        = 0x1702;

    const GLenum TEXTURE_CUBE_MAP               = 0x8513;
    const GLenum TEXTURE_BINDING_CUBE_MAP       = 0x8514;
    const GLenum TEXTURE_CUBE_MAP_POSITIVE_X    = 0x8515;
    const GLenum TEXTURE_CUBE_MAP_NEGATIVE_X    = 0x8516;
    const GLenum TEXTURE_CUBE_MAP_POSITIVE_Y    = 0x8517;
    const GLenum TEXTURE_CUBE_MAP_NEGATIVE_Y    = 0x8518;
    const GLenum TEXTURE_CUBE_MAP_POSITIVE_Z    = 0x8519;
    const GLenum TEXTURE_CUBE_MAP_NEGATIVE_Z    = 0x851A;
    const GLenum MAX_CUBE_MAP_TEXTURE_SIZE      = 0x851C;

    /* TextureUnit */
    const GLenum TEXTURE0                       = 0x84C0;
    const GLenum TEXTURE1                       = 0x84C1;
    const GLenum TEXTURE2                       = 0x84C2;
    const GLenum TEXTURE3                       = 0x84C3;
    const GLenum TEXTURE4                       = 0x84C4;
    const GLenum TEXTURE5                       = 0x84C5;
    const GLenum TEXTURE6                       = 0x84C6;
    const GLenum TEXTURE7                       = 0x84C7;
    const GLenum TEXTURE8                       = 0x84C8;
    const GLenum TEXTURE9                       = 0x84C9;
    const GLenum TEXTURE10                      = 0x84CA;
    const GLenum TEXTURE11                      = 0x84CB;
    const GLenum TEXTURE12                      = 0x84CC;
    const GLenum TEXTURE13                      = 0x84CD;
    const GLenum TEXTURE14                      = 0x84CE;
    const GLenum TEXTURE15                      = 0x84CF;
    const GLenum TEXTURE16                      = 0x84D0;
    const GLenum TEXTURE17                      = 0x84D1;
    const GLenum TEXTURE18                      = 0x84D2;
    const GLenum TEXTURE19                      = 0x84D3;
    const GLenum TEXTURE20                      = 0x84D4;
    const GLenum TEXTURE21                      = 0x84D5;
    const GLenum TEXTURE22                      = 0x84D6;
    const GLenum TEXTURE23                      = 0x84D7;
    const GLenum TEXTURE24                      = 0x84D8;
    const GLenum TEXTURE25                      = 0x84D9;
    const GLenum TEXTURE26                      = 0x84DA;
    const GLenum TEXTURE27                      = 0x84DB;
    const GLenum TEXTURE28                      = 0x84DC;
    const GLenum TEXTURE29                      = 0x84DD;
    const GLenum TEXTURE30                      = 0x84DE;
    const GLenum TEXTURE31                      = 0x84DF;
    const GLenum ACTIVE_TEXTURE                 = 0x84E0;

    /* TextureWrapMode */
    const GLenum REPEAT                         = 0x2901;
    const GLenum CLAMP_TO_EDGE                  = 0x812F;
    const GLenum MIRRORED_REPEAT                = 0x8370;

    /* Uniform Types */
    const GLenum FLOAT_VEC2                     = 0x8B50;
    const GLenum FLOAT_VEC3                     = 0x8B51;
    const GLenum FLOAT_VEC4                     = 0x8B52;
    const GLenum INT_VEC2                       = 0x8B53;
    const GLenum INT_VEC3                       = 0x8B54;
    const GLenum INT_VEC4                       = 0x8B55;
    const GLenum BOOL                           = 0x8B56;
    const GLenum BOOL_VEC2                      = 0x8B57;
    const GLenum BOOL_VEC3                      = 0x8B58;
    const GLenum BOOL_VEC4                      = 0x8B59;
    const GLenum FLOAT_MAT2                     = 0x8B5A;
    const GLenum FLOAT_MAT3                     = 0x8B5B;
    const GLenum FLOAT_MAT4                     = 0x8B5C;
    const GLenum SAMPLER_2D                     = 0x8B5E;
    const GLenum SAMPLER_CUBE                   = 0x8B60;

    /* Vertex Arrays */
    const GLenum VERTEX_ATTRIB_ARRAY_ENABLED        = 0x8622;
    const GLenum VERTEX_ATTRIB_ARRAY_SIZE           = 0x8623;
    const GLenum VERTEX_ATTRIB_ARRAY_STRIDE         = 0x8624;
    const GLenum VERTEX_ATTRIB_ARRAY_TYPE           = 0x8625;
    const GLenum VERTEX_ATTRIB_ARRAY_NORMALIZED     = 0x886A;
    const GLenum VERTEX_ATTRIB_ARRAY_POINTER        = 0x8645;
    const GLenum VERTEX_ATTRIB_ARRAY_BUFFER_BINDING = 0x889F;

    /* Read Format */
    const GLenum IMPLEMENTATION_COLOR_READ_TYPE   = 0x8B9A;
    const GLenum IMPLEMENTATION_COLOR_READ_FORMAT = 0x8B9B;

    /* Shader Source */
    const GLenum COMPILE_STATUS                 = 0x8B81;

    /* Shader Precision-Specified Types */
    const GLenum LOW_FLOAT                      = 0x8DF0;
    const GLenum MEDIUM_FLOAT                   = 0x8DF1;
    const GLenum HIGH_FLOAT                     = 0x8DF2;
    const GLenum LOW_INT                        = 0x8DF3;
    const GLenum MEDIUM_INT                     = 0x8DF4;
    const GLenum HIGH_INT                       = 0x8DF5;

    /* Framebuffer Object. */
    const GLenum FRAMEBUFFER                    = 0x8D40;
    const GLenum RENDERBUFFER                   = 0x8D41;

    const GLenum RGBA4                          = 0x8056;
    const GLenum RGB5_A1                        = 0x8057;
    const GLenum RGBA8                          = 0x8058;
    const GLenum RGB565                         = 0x8D62;
    const GLenum DEPTH_COMPONENT16              = 0x81A5;
    const GLenum STENCIL_INDEX8                 = 0x8D48;
    const GLenum DEPTH_STENCIL                  = 0x84F9;

    const GLenum RENDERBUFFER_WIDTH             = 0x8D42;
    const GLenum RENDERBUFFER_HEIGHT            = 0x8D43;
    const GLenum RENDERBUFFER_INTERNAL_FORMAT   = 0x8D44;
    const GLenum RENDERBUFFER_RED_SIZE          = 0x8D50;
    const GLenum RENDERBUFFER_GREEN_SIZE        = 0x8D51;
    const GLenum RENDERBUFFER_BLUE_SIZE         = 0x8D52;
    const GLenum RENDERBUFFER_ALPHA_SIZE        = 0x8D53;
    const GLenum RENDERBUFFER_DEPTH_SIZE        = 0x8D54;
    const GLenum RENDERBUFFER_STENCIL_SIZE      = 0x8D55;

    const GLenum FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE           = 0x8CD0;
    const GLenum FRAMEBUFFER_ATTACHMENT_OBJECT_NAME           = 0x8CD1;
    const GLenum FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL         = 0x8CD2;
    const GLenum FRAMEBUFFER_ATTACHMENT_TEXTURE_CUBE_MAP_FACE = 0x8CD3;

    const GLenum COLOR_ATTACHMENT0              = 0x8CE0;
    const GLenum DEPTH_ATTACHMENT               = 0x8D00;
    const GLenum STENCIL_ATTACHMENT             = 0x8D20;
    const GLenum DEPTH_STENCIL_ATTACHMENT       = 0x821A;

    const GLenum NONE                           = 0;

    const GLenum FRAMEBUFFER_COMPLETE                      = 0x8CD5;
    const GLenum FRAMEBUFFER_INCOMPLETE_ATTACHMENT         = 0x8CD6;
    const GLenum FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT = 0x8CD7;
    const GLenum FRAMEBUFFER_INCOMPLETE_DIMENSIONS         = 0x8CD9;
    const GLenum FRAMEBUFFER_UNSUPPORTED                   = 0x8CDD;

    const GLenum FRAMEBUFFER_BINDING            = 0x8CA6;
    const GLenum RENDERBUFFER_BINDING           = 0x8CA7;
    const GLenum MAX_RENDERBUFFER_SIZE          = 0x84E8;

    const GLenum INVALID_FRAMEBUFFER_OPERATION  = 0x0506;

    /* WebGL-specific enums */
    const GLenum UNPACK_FLIP_Y_WEBGL            = 0x9240;
    const GLenum UNPACK_PREMULTIPLY_ALPHA_WEBGL = 0x9241;
    const GLenum CONTEXT_LOST_WEBGL             = 0x9242;
    const GLenum UNPACK_COLORSPACE_CONVERSION_WEBGL = 0x9243;
    const GLenum BROWSER_DEFAULT_WEBGL          = 0x9244;

    readonly attribute (HTMLCanvasElement or OffscreenCanvas) canvas;
    readonly attribute GLsizei drawingBufferWidth;
    readonly attribute GLsizei drawingBufferHeight;
    readonly attribute GLenum drawingBufferFormat;

    /* Upon context creation, drawingBufferColorSpace and unpackColorSpace both
       default to the value "srgb". */
    attribute PredefinedColorSpace drawingBufferColorSpace;
    attribute PredefinedColorSpace unpackColorSpace;

    [WebGLHandlesContextLoss] WebGLContextAttributes? getContextAttributes();
    [WebGLHandlesContextLoss] boolean isContextLost();

    sequence<DOMString>? getSupportedExtensions();
    object? getExtension(DOMString name);

    undefined drawingBufferStorage(GLenum sizedFormat, unsigned long width, unsigned long height);

    undefined activeTexture(GLenum texture);
    undefined attachShader(WebGLProgram program, WebGLShader shader);
    undefined bindAttribLocation(WebGLProgram program, GLuint index, DOMString name);
    undefined bindBuffer(GLenum target, WebGLBuffer? buffer);
    undefined bindFramebuffer(GLenum target, WebGLFramebuffer? framebuffer);
    undefined bindRenderbuffer(GLenum target, WebGLRenderbuffer? renderbuffer);
    undefined bindTexture(GLenum target, WebGLTexture? texture);
    undefined blendColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha);
    undefined blendEquation(GLenum mode);
    undefined blendEquationSeparate(GLenum modeRGB, GLenum modeAlpha);
    undefined blendFunc(GLenum sfactor, GLenum dfactor);
    undefined blendFuncSeparate(GLenum srcRGB, GLenum dstRGB,
                                GLenum srcAlpha, GLenum dstAlpha);

    [WebGLHandlesContextLoss] GLenum checkFramebufferStatus(GLenum target);
    undefined clear(GLbitfield mask);
    undefined clearColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha);
    undefined clearDepth(GLclampf depth);
    undefined clearStencil(GLint s);
    undefined colorMask(GLboolean red, GLboolean green, GLboolean blue, GLboolean alpha);
    undefined compileShader(WebGLShader shader);

    undefined copyTexImage2D(GLenum target, GLint level, GLenum internalformat,
                             GLint x, GLint y, GLsizei width, GLsizei height,
                             GLint border);
    undefined copyTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
                                GLint x, GLint y, GLsizei width, GLsizei height);

    WebGLBuffer createBuffer();
    WebGLFramebuffer createFramebuffer();
    WebGLProgram createProgram();
    WebGLRenderbuffer createRenderbuffer();
    WebGLShader? createShader(GLenum type);
    WebGLTexture createTexture();

    undefined cullFace(GLenum mode);

    undefined deleteBuffer(WebGLBuffer? buffer);
    undefined deleteFramebuffer(WebGLFramebuffer? framebuffer);
    undefined deleteProgram(WebGLProgram? program);
    undefined deleteRenderbuffer(WebGLRenderbuffer? renderbuffer);
    undefined deleteShader(WebGLShader? shader);
    undefined deleteTexture(WebGLTexture? texture);

    undefined depthFunc(GLenum func);
    undefined depthMask(GLboolean flag);
    undefined depthRange(GLclampf zNear, GLclampf zFar);
    undefined detachShader(WebGLProgram program, WebGLShader shader);
    undefined disable(GLenum cap);
    undefined disableVertexAttribArray(GLuint index);
    undefined drawArrays(GLenum mode, GLint first, GLsizei count);
    undefined drawElements(GLenum mode, GLsizei count, GLenum type, GLintptr offset);

    undefined enable(GLenum cap);
    undefined enableVertexAttribArray(GLuint index);
    undefined finish();
    undefined flush();
    undefined framebufferRenderbuffer(GLenum target, GLenum attachment,
                                      GLenum renderbuffertarget,
                                      WebGLRenderbuffer? renderbuffer);
    undefined framebufferTexture2D(GLenum target, GLenum attachment, GLenum textarget,
                                   WebGLTexture? texture, GLint level);
    undefined frontFace(GLenum mode);

    undefined generateMipmap(GLenum target);

    WebGLActiveInfo? getActiveAttrib(WebGLProgram program, GLuint index);
    WebGLActiveInfo? getActiveUniform(WebGLProgram program, GLuint index);
    sequence<WebGLShader>? getAttachedShaders(WebGLProgram program);

    [WebGLHandlesContextLoss] GLint getAttribLocation(WebGLProgram program, DOMString name);

    any getBufferParameter(GLenum target, GLenum pname);
    any getParameter(GLenum pname);

    [WebGLHandlesContextLoss] GLenum getError();

    any getFramebufferAttachmentParameter(GLenum target, GLenum attachment,
                                          GLenum pname);
    any getProgramParameter(WebGLProgram program, GLenum pname);
    DOMString? getProgramInfoLog(WebGLProgram program);
    any getRenderbufferParameter(GLenum target, GLenum pname);
    any getShaderParameter(WebGLShader shader, GLenum pname);
    WebGLShaderPrecisionFormat? getShaderPrecisionFormat(GLenum shadertype, GLenum precisiontype);
    DOMString? getShaderInfoLog(WebGLShader shader);

    DOMString? getShaderSource(WebGLShader shader);

    any getTexParameter(GLenum target, GLenum pname);

    any getUniform(WebGLProgram program, WebGLUniformLocation location);

    WebGLUniformLocation? getUniformLocation(WebGLProgram program, DOMString name);

    any getVertexAttrib(GLuint index, GLenum pname);

    [WebGLHandlesContextLoss] GLintptr getVertexAttribOffset(GLuint index, GLenum pname);

    undefined hint(GLenum target, GLenum mode);
    [WebGLHandlesContextLoss] GLboolean isBuffer(WebGLBuffer? buffer);
    [WebGLHandlesContextLoss] GLboolean isEnabled(GLenum cap);
    [WebGLHandlesContextLoss] GLboolean isFramebuffer(WebGLFramebuffer? framebuffer);
    [WebGLHandlesContextLoss] GLboolean isProgram(WebGLProgram? program);
    [WebGLHandlesContextLoss] GLboolean isRenderbuffer(WebGLRenderbuffer? renderbuffer);
    [WebGLHandlesContextLoss] GLboolean isShader(WebGLShader? shader);
    [WebGLHandlesContextLoss] GLboolean isTexture(WebGLTexture? texture);
    undefined lineWidth(GLfloat width);
    undefined linkProgram(WebGLProgram program);
    undefined pixelStorei(GLenum pname, GLint param);
    undefined polygonOffset(GLfloat factor, GLfloat units);

    undefined renderbufferStorage(GLenum target, GLenum internalformat,
                                  GLsizei width, GLsizei height);
    undefined sampleCoverage(GLclampf value, GLboolean invert);
    undefined scissor(GLint x, GLint y, GLsizei width, GLsizei height);

    undefined shaderSource(WebGLShader shader, DOMString source);

    undefined stencilFunc(GLenum func, GLint ref, GLuint mask);
    undefined stencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask);
    undefined stencilMask(GLuint mask);
    undefined stencilMaskSeparate(GLenum face, GLuint mask);
    undefined stencilOp(GLenum fail, GLenum zfail, GLenum zpass);
    undefined stencilOpSeparate(GLenum face, GLenum fail, GLenum zfail, GLenum zpass);

    undefined texParameterf(GLenum target, GLenum pname, GLfloat param);
    undefined texParameteri(GLenum target, GLenum pname, GLint param);

    undefined uniform1f(WebGLUniformLocation? location, GLfloat x);
    undefined uniform2f(WebGLUniformLocation? location, GLfloat x, GLfloat y);
    undefined uniform3f(WebGLUniformLocation? location, GLfloat x, GLfloat y, GLfloat z);
    undefined uniform4f(WebGLUniformLocation? location, GLfloat x, GLfloat y, GLfloat z, GLfloat w);

    undefined uniform1i(WebGLUniformLocation? location, GLint x);
    undefined uniform2i(WebGLUniformLocation? location, GLint x, GLint y);
    undefined uniform3i(WebGLUniformLocation? location, GLint x, GLint y, GLint z);
    undefined uniform4i(WebGLUniformLocation? location, GLint x, GLint y, GLint z, GLint w);

    undefined useProgram(WebGLProgram? program);
    undefined validateProgram(WebGLProgram program);

    undefined vertexAttrib1f(GLuint index, GLfloat x);
    undefined vertexAttrib2f(GLuint index, GLfloat x, GLfloat y);
    undefined vertexAttrib3f(GLuint index, GLfloat x, GLfloat y, GLfloat z);
    undefined vertexAttrib4f(GLuint index, GLfloat x, GLfloat y, GLfloat z, GLfloat w);

    undefined vertexAttrib1fv(GLuint index, Float32List values);
    undefined vertexAttrib2fv(GLuint index, Float32List values);
    undefined vertexAttrib3fv(GLuint index, Float32List values);
    undefined vertexAttrib4fv(GLuint index, Float32List values);

    undefined vertexAttribPointer(GLuint index, GLint size, GLenum type,
                                  GLboolean normalized, GLsizei stride, GLintptr offset);

    undefined viewport(GLint x, GLint y, GLsizei width, GLsizei height);
};

interface mixin WebGLRenderingContextOverloads
{
    undefined bufferData(GLenum target, GLsizeiptr size, GLenum usage);
    undefined bufferData(GLenum target, AllowSharedBufferSource? data, GLenum usage);
    undefined bufferSubData(GLenum target, GLintptr offset, AllowSharedBufferSource data);

    undefined compressedTexImage2D(GLenum target, GLint level, GLenum internalformat,
                                   GLsizei width, GLsizei height, GLint border,
                                   [AllowShared] ArrayBufferView data);
    undefined compressedTexSubImage2D(GLenum target, GLint level,
                                      GLint xoffset, GLint yoffset,
                                      GLsizei width, GLsizei height, GLenum format,
                                      [AllowShared] ArrayBufferView data);

    undefined readPixels(GLint x, GLint y, GLsizei width, GLsizei height,
                         GLenum format, GLenum type, [AllowShared] ArrayBufferView? pixels);

    undefined texImage2D(GLenum target, GLint level, GLint internalformat,
                         GLsizei width, GLsizei height, GLint border, GLenum format,
                         GLenum type, [AllowShared] ArrayBufferView? pixels);
    undefined texImage2D(GLenum target, GLint level, GLint internalformat,
                         GLenum format, GLenum type, TexImageSource source); // May throw DOMException

    undefined texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
                            GLsizei width, GLsizei height,
                            GLenum format, GLenum type, [AllowShared] ArrayBufferView? pixels);
    undefined texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
                            GLenum format, GLenum type, TexImageSource source); // May throw DOMException

    undefined uniform1fv(WebGLUniformLocation? location, Float32List v);
    undefined uniform2fv(WebGLUniformLocation? location, Float32List v);
    undefined uniform3fv(WebGLUniformLocation? location, Float32List v);
    undefined uniform4fv(WebGLUniformLocation? location, Float32List v);

    undefined uniform1iv(WebGLUniformLocation? location, Int32List v);
    undefined uniform2iv(WebGLUniformLocation? location, Int32List v);
    undefined uniform3iv(WebGLUniformLocation? location, Int32List v);
    undefined uniform4iv(WebGLUniformLocation? location, Int32List v);

    undefined uniformMatrix2fv(WebGLUniformLocation? location, GLboolean transpose, Float32List value);
    undefined uniformMatrix3fv(WebGLUniformLocation? location, GLboolean transpose, Float32List value);
    undefined uniformMatrix4fv(WebGLUniformLocation? location, GLboolean transpose, Float32List value);
};

[Exposed=(Window,Worker)]
interface WebGLRenderingContext
{
};
WebGLRenderingContext includes WebGLRenderingContextBase;
WebGLRenderingContext includes WebGLRenderingContextOverloads;

Attributes

The following attributes are available:

canvas of type (HTMLCanvasElement or OffscreenCanvas): A reference to the canvas element or OffscreenCanvas object which created this context.
drawingBufferWidth of type GLsizei: The actual width of the drawing buffer. May be different from the width attribute of the HTMLCanvasElement if the implementation is unable to satisfy the requested widthor height.
drawingBufferHeight of type GLsizei: The actual height of the drawing buffer. May be different from the height attribute of the HTMLCanvasElement if the implementation is unable to satisfy the requested width or height.
drawingBufferFormat of type GLenum: The current effective format of the drawing buffer. Initially RGBA8 or RGB8 for alpha:true and alpha:false respectively.
drawingBufferColorSpace of type PredefinedColorSpace (specification): The color space used to interpret the drawing buffer's content values. Changing this attribute causes the drawing buffer to be reallocated; its current contents are lost. This attribute affects the on-screen display of the rendering context, and the interpretation of this context's drawing buffer when it is drawn to a 2D canvas context, or uploaded to textures in another WebGL or WebGPU rendering context.
unpackColorSpace of type PredefinedColorSpace (specification): The color space into which TexImageSource sources are converted when uploading them to textures in this context.

Getting information about the context

[WebGLHandlesContextLoss] WebGLContextAttributes? getContextAttributes(): If the webgl context lost flag is set, returns null. Otherwise, returns a copy of the actual context parameters.

Setting and getting state

OpenGL ES 2.0 maintains state values for use in rendering. All the calls in this group behave identically to their OpenGL counterparts unless otherwise noted.

void activeTexture(GLenum texture) (OpenGL ES 2.0 §3.7, man page)

void blendColor(GLfloat red, GLfloat green, GLfloat blue, GLfloat alpha) (OpenGL ES 2.0 §4.1.6, man page)

blendColor clamps its arguments to the range 0 to 1 in WebGL 1.0, unless EXT_color_buffer_half_float or WEBGL_color_buffer_float are enabled.

void blendEquation(GLenum mode) (OpenGL ES 2.0 §4.1.6, man page)

void blendEquationSeparate(GLenum modeRGB, GLenum modeAlpha) (OpenGL ES 2.0 §4.1.6, man page)

void blendFunc(GLenum sfactor, GLenum dfactor) (OpenGL ES 2.0 §4.1.6, man page)

See Blending With Constant Color for limitations imposed by WebGL.

void blendFuncSeparate(GLenum srcRGB, GLenum dstRGB, GLenum srcAlpha, GLenum dstAlpha) (OpenGL ES 2.0 §4.1.6, man page)

See Blending With Constant Color for limitations imposed by WebGL.

void clearColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha) (OpenGL ES 2.0 §4.2.3, man page)

void clearDepth(GLclampf depth) (OpenGL ES 2.0 §4.2.3, man page)

depth value is clamped to the range 0 to 1.

void clearStencil(GLint s) (OpenGL ES 2.0 §4.2.3, man page)

void colorMask(GLboolean red, GLboolean green, GLboolean blue, GLboolean alpha) (OpenGL ES 2.0 §4.2.2, man page)

void cullFace(GLenum mode) (OpenGL ES 2.0 §3.5.1, man page)

void depthFunc(GLenum func) (OpenGL ES 2.0 §4.1.5, man page)

void depthMask(GLboolean flag) (OpenGL ES 2.0 §4.2.2, man page)

void depthRange(GLclampf zNear, GLclampf zFar) (OpenGL ES 2.0 §2.12.1, man page)

zNear and zFar values are clamped to the range 0 to 1 and zNear must be less than or equal to zFar; see Viewport Depth Range.

void disable(GLenum cap) (man page)

void enable(GLenum cap) (man page)

void frontFace(GLenum mode) (OpenGL ES 2.0 §3.5.1, man page)

any getParameter(GLenum pname) (glGet OpenGL ES 2.0 man page) (glGetString OpenGL ES 2.0 man page)

Return the value for the passed pname. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
ACTIVE_TEXTURE	GLenum
ALIASED_LINE_WIDTH_RANGE	Float32Array (with 2 elements)
ALIASED_POINT_SIZE_RANGE	Float32Array (with 2 elements)
ALPHA_BITS	GLint
ARRAY_BUFFER_BINDING	WebGLBuffer
BLEND	GLboolean
BLEND_COLOR	Float32Array (with 4 values)
BLEND_DST_ALPHA	GLenum
BLEND_DST_RGB	GLenum
BLEND_EQUATION_ALPHA	GLenum
BLEND_EQUATION_RGB	GLenum
BLEND_SRC_ALPHA	GLenum
BLEND_SRC_RGB	GLenum
BLUE_BITS	GLint
COLOR_CLEAR_VALUE	Float32Array (with 4 values)
COLOR_WRITEMASK	sequence<GLboolean> (with 4 values)
COMPRESSED_TEXTURE_FORMATS	Uint32Array
CULL_FACE	GLboolean
CULL_FACE_MODE	GLenum
CURRENT_PROGRAM	WebGLProgram
DEPTH_BITS	GLint
DEPTH_CLEAR_VALUE	GLfloat
DEPTH_FUNC	GLenum
DEPTH_RANGE	Float32Array (with 2 elements)
DEPTH_TEST	GLboolean
DEPTH_WRITEMASK	GLboolean
DITHER	GLboolean
ELEMENT_ARRAY_BUFFER_BINDING	WebGLBuffer
FRAMEBUFFER_BINDING	WebGLFramebuffer
FRONT_FACE	GLenum
GENERATE_MIPMAP_HINT	GLenum
GREEN_BITS	GLint
IMPLEMENTATION_COLOR_READ_FORMAT	GLenum
IMPLEMENTATION_COLOR_READ_TYPE	GLenum
LINE_WIDTH	GLfloat
MAX_COMBINED_TEXTURE_IMAGE_UNITS	GLint
MAX_CUBE_MAP_TEXTURE_SIZE	GLint
MAX_FRAGMENT_UNIFORM_VECTORS	GLint
MAX_RENDERBUFFER_SIZE	GLint
MAX_TEXTURE_IMAGE_UNITS	GLint
MAX_TEXTURE_SIZE	GLint
MAX_VARYING_VECTORS	GLint
MAX_VERTEX_ATTRIBS	GLint
MAX_VERTEX_TEXTURE_IMAGE_UNITS	GLint
MAX_VERTEX_UNIFORM_VECTORS	GLint
MAX_VIEWPORT_DIMS	Int32Array (with 2 elements)
PACK_ALIGNMENT	GLint
POLYGON_OFFSET_FACTOR	GLfloat
POLYGON_OFFSET_FILL	GLboolean
POLYGON_OFFSET_UNITS	GLfloat
RED_BITS	GLint
RENDERBUFFER_BINDING	WebGLRenderbuffer
RENDERER	DOMString
SAMPLE_ALPHA_TO_COVERAGE	GLboolean
SAMPLE_BUFFERS	GLint
SAMPLE_COVERAGE	GLboolean
SAMPLE_COVERAGE_INVERT	GLboolean
SAMPLE_COVERAGE_VALUE	GLfloat
SAMPLES	GLint
SCISSOR_BOX	Int32Array (with 4 elements)
SCISSOR_TEST	GLboolean
SHADING_LANGUAGE_VERSION	DOMString
STENCIL_BACK_FAIL	GLenum
STENCIL_BACK_FUNC	GLenum
STENCIL_BACK_PASS_DEPTH_FAIL	GLenum
STENCIL_BACK_PASS_DEPTH_PASS	GLenum
STENCIL_BACK_REF	GLint
STENCIL_BACK_VALUE_MASK	GLuint
STENCIL_BACK_WRITEMASK	GLuint
STENCIL_BITS	GLint
STENCIL_CLEAR_VALUE	GLint
STENCIL_FAIL	GLenum
STENCIL_FUNC	GLenum
STENCIL_PASS_DEPTH_FAIL	GLenum
STENCIL_PASS_DEPTH_PASS	GLenum
STENCIL_REF	GLint
STENCIL_TEST	GLboolean
STENCIL_VALUE_MASK	GLuint
STENCIL_WRITEMASK	GLuint
SUBPIXEL_BITS	GLint
TEXTURE_BINDING_2D	WebGLTexture
TEXTURE_BINDING_CUBE_MAP	WebGLTexture
UNPACK_ALIGNMENT	GLint
UNPACK_COLORSPACE_CONVERSION_WEBGL	GLenum
UNPACK_FLIP_Y_WEBGL	GLboolean
UNPACK_PREMULTIPLY_ALPHA_WEBGL	GLboolean
VENDOR	DOMString
VERSION	DOMString
VIEWPORT	Int32Array (with 4 elements)

All queries returning sequences or typed arrays return a new object each time.

If pname is not in the table above, generates an INVALID_ENUM error and returns null.

If pname is IMPLEMENTATION_COLOR_READ_FORMAT or IMPLEMENTATION_COLOR_READ_TYPE, and the currently bound framebuffer is not framebuffer complete, generates an INVALID_OPERATION error and returns null.

The following pname arguments return a string describing some aspect of the current WebGL implementation:

VERSION	Returns a version or release number of the form `WebGL<space>1.0<optional><space><vendor-specific information></optional>`.
SHADING_LANGUAGE_VERSION	Returns a version or release number of the form `WebGL<space>GLSL<space>ES<space>1.0<optional><space><vendor-specific information></optional>`.
VENDOR	Returns the company responsible for this WebGL implementation. This name does not change from release to release.
RENDERER	Returns the name of the renderer. This name is typically specific to a particular configuration of a hardware platform. It does not change from release to release.

See Extension Queries for information on querying the available extensions in the current WebGL implementation.

[WebGLHandlesContextLoss] GLenum getError() (OpenGL ES 2.0 §2.5, man page)

If the context's webgl context lost flag is set, returns CONTEXT_LOST_WEBGL the first time this method is called. Afterward, returns NO_ERROR until the context has been restored.

void hint(GLenum target, GLenum mode) (OpenGL ES 2.0 §5.2, man page)

[WebGLHandlesContextLoss] GLboolean isEnabled(GLenum cap) (OpenGL ES 2.0 §6.1.1, man page)

For any isEnabled query, the same boolean value can be obtained via getParameter.

Returns false if the context's webgl context lost flag is set.

void lineWidth(GLfloat width) (OpenGL ES 2.0 §3.4, man page)

See NaN Line Width for restrictions specified for WebGL.

void pixelStorei(GLenum pname, GLint param) (OpenGL ES 2.0 §3.6.1, man page)

In addition to the parameters in the OpenGL ES 2.0 specification, the WebGL specification accepts the parameters UNPACK_FLIP_Y_WEBGL, UNPACK_PREMULTIPLY_ALPHA_WEBGL and UNPACK_COLORSPACE_CONVERSION_WEBGL. See Pixel Storage Parameters for documentation of these parameters.

void polygonOffset(GLfloat factor, GLfloat units) (OpenGL ES 2.0 §3.5.2, man page)

void sampleCoverage(GLclampf value, GLboolean invert) (OpenGL ES 2.0 §4.1.3, man page)

void stencilFunc(GLenum func, GLint ref, GLuint mask) (OpenGL ES 2.0 §4.1.4, man page)

void stencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask) (OpenGL ES 2.0 §4.1.4, man page)

See Stencil Separate Mask and Reference Value for information on WebGL specific limitations to the allowable argument values.

void stencilMask(GLuint mask) (OpenGL ES 2.0 §4.2.2, man page)

See Stencil Separate Mask and Reference Value for information on WebGL specific limitations to the allowable mask values.

void stencilMaskSeparate(GLenum face, GLuint mask) (OpenGL ES 2.0 §4.2.2, man page)

void stencilOp(GLenum fail, GLenum zfail, GLenum zpass) (OpenGL ES 2.0 §4.1.4, man page)

void stencilOpSeparate(GLenum face, GLenum fail, GLenum zfail, GLenum zpass) (OpenGL ES 2.0 §4.1.4, man page)

Viewing and clipping

Drawing commands can only modify pixels inside the currently bound framebuffer. In addition, the viewport and the scissor box affect drawing.

The viewport specifies the affine transformation of x and y from normalized device coordinates to window coordinates. The size of the viewport is initially determined as specified in section The WebGL Viewport. The scissor box defines a rectangle which constrains drawing. When the scissor test is enabled only pixels that lie within the scissor box can be modified by drawing commands including clear, and primitives can only be drawn inside the intersection of the viewport, the currently bound framebuffer, and the scissor box. When the scissor test is not enabled primitives can only be drawn inside the intersection of the viewport and the currently bound framebuffer.

void scissor(GLint x, GLint y, GLsizei width, GLsizei height) (OpenGL ES 2.0 §4.1.2, man page)
void viewport(GLint x, GLint y, GLsizei width, GLsizei height) (OpenGL ES 2.0 §2.12.1, man page)

Buffer objects

Buffer objects (sometimes referred to as VBOs) hold vertex attribute data for the GLSL shaders.

void bindBuffer(GLenum target, WebGLBuffer? buffer) (OpenGL ES 2.0 §2.9, man page)

If buffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Binds the given WebGLBuffer object to the given binding point (target), either ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER. If the buffer is null then any buffer currently bound to this target is unbound. A given WebGLBuffer object may only be bound to one of the ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER target in its lifetime. An attempt to bind a buffer object to the other target will generate an INVALID_OPERATION error, and the current binding will remain untouched. An attempt to bind an object marked for deletion will generate an INVALID_OPERATION error, and the current binding will remain untouched.

void bufferData(GLenum target, GLsizeiptr size, GLenum usage) (OpenGL ES 2.0 §2.9, man page)

Set the size of the currently bound WebGLBuffer object for the passed target. The buffer is initialized to 0.

void bufferData(GLenum target, AllowSharedBufferSource? data, GLenum usage) (OpenGL ES 2.0 §2.9, man page)

Set the size of the currently bound WebGLBuffer object for the passed target to the size of the passed data, then write the contents of data to the buffer object.

If the passed data is null then an INVALID_VALUE error is generated.

void bufferSubData(GLenum target, GLintptr offset, AllowSharedBufferSource data) (OpenGL ES 2.0 §2.9, man page)

For the WebGLBuffer object bound to the passed target write the passed data starting at the passed offset. If the data would be written past the end of the buffer object an INVALID_VALUE error is generated. If data is null then an INVALID_VALUE error is generated.

WebGLBuffer createBuffer() (OpenGL ES 2.0 §2.9, similar to glGenBuffers)

Create a WebGLBuffer object and initialize it with a buffer object name as if by calling glGenBuffers.

void deleteBuffer(WebGLBuffer? buffer) (OpenGL ES 2.0 §2.9, similar to glDeleteBuffers)

If buffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Mark for deletion the buffer object contained in the passed WebGLBuffer, as if by calling glDeleteBuffers. If the object has already been marked for deletion, the call has no effect. Note that underlying GL object will be automatically marked for deletion when the JS object is destroyed, however this method allows authors to mark an object for deletion early.

any getBufferParameter(GLenum target, GLenum pname) (OpenGL ES 2.0 §6.1.3, similar to glGetBufferParameteriv)

Return the value for the passed pname. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
BUFFER_SIZE	GLint
BUFFER_USAGE	GLenum

If pname is not in the table above, generates an INVALID_ENUM error.

If an OpenGL error is generated, returns null.

[WebGLHandlesContextLoss] GLboolean isBuffer(WebGLBuffer? buffer) (OpenGL ES 2.0 §6.1.6, man page)

Return true if the passed WebGLBuffer is valid and false otherwise.

Returns false if the buffer was generated by a different WebGLRenderingContext than this one.

Returns false if the buffer's invalidated flag is set.

Framebuffer objects

Framebuffer objects provide an alternative rendering target to the drawing buffer. They are a collection of color, alpha, depth and stencil buffers and are often used to render an image that will later be used as a texture.

void bindFramebuffer(GLenum target, WebGLFramebuffer? framebuffer) (OpenGL ES 2.0 §4.4.1, man page)

If framebuffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Bind the given WebGLFramebuffer object to the given binding point (target), which must be FRAMEBUFFER. If framebuffer is null, the default framebuffer provided by the context is bound and attempts to modify or query state on target FRAMEBUFFER will generate an INVALID_OPERATION error. An attempt to bind an object marked for deletion will generate an INVALID_OPERATION error, and the current binding will remain untouched.

[WebGLHandlesContextLoss] GLenum checkFramebufferStatus(GLenum target) (OpenGL ES 2.0 §4.4.5, man page)

Returns FRAMEBUFFER_UNSUPPORTED if the context's webgl context lost flag is set.

WebGLFramebuffer createFramebuffer() (OpenGL ES 2.0 §4.4.1, similar to glGenFramebuffers)

Create a WebGLFramebuffer object and initialize it with a framebuffer object name as if by calling glGenFramebuffers.

void deleteFramebuffer(WebGLFramebuffer? buffer) (OpenGL ES 2.0 §4.4.1, similar to glDeleteFramebuffers)

If framebuffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Mark for deletion the framebuffer object contained in the passed WebGLFramebuffer, as if by calling glDeleteFramebuffers. If the object has already been marked for deletion, the call has no effect. Note that underlying GL object will be automatically marked for deletion when the JS object is destroyed, however this method allows authors to mark an object for deletion early.

void framebufferRenderbuffer(GLenum target, GLenum attachment, GLenum renderbuffertarget, WebGLRenderbuffer? renderbuffer) (OpenGL ES 2.0 §4.4.3, man page)

If renderbuffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

void framebufferTexture2D(GLenum target, GLenum attachment, GLenum textarget, WebGLTexture? texture, GLint level) (OpenGL ES 2.0 §4.4.3, man page)

If texture was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

any getFramebufferAttachmentParameter(GLenum target, GLenum attachment, GLenum pname) (OpenGL ES 2.0 §6.1.3, similar to glGetFramebufferAttachmentParameteriv)

Return the value for the passed pname given the passed target and attachment. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
FRAMEBUFFER_ATTACHMENT_OBJECT_TYPE	GLenum
FRAMEBUFFER_ATTACHMENT_OBJECT_NAME	WebGLRenderbuffer or WebGLTexture
FRAMEBUFFER_ATTACHMENT_TEXTURE_LEVEL	GLint
FRAMEBUFFER_ATTACHMENT_TEXTURE_CUBE_MAP_FACE	GLint

If pname is not in the table above, generates an INVALID_ENUM error.

If an OpenGL error is generated, returns null.

[WebGLHandlesContextLoss] GLboolean isFramebuffer(WebGLFramebuffer? framebuffer) (OpenGL ES 2.0 §6.1.7, man page)

Return true if the passed WebGLFramebuffer is valid and false otherwise.

Returns false if the framebuffer was generated by a different WebGLRenderingContext than this one.

Returns false if the framebuffer's invalidated flag is set.

Renderbuffer objects

Renderbuffer objects are used to provide storage for the individual buffers used in a framebuffer object.

void bindRenderbuffer(GLenum target, WebGLRenderbuffer? renderbuffer) (OpenGL ES 2.0 §4.4.3, man page)

If renderbuffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Bind the given WebGLRenderbuffer object to the given binding point (target), which must be RENDERBUFFER. If renderbuffer is null the renderbuffer object currently bound to this target is unbound. An attempt to bind an object marked for deletion will generate an INVALID_OPERATION error, and the current binding will remain untouched.

WebGLRenderbuffer createRenderbuffer() (OpenGL ES 2.0 §4.4.3, similar to glGenRenderbuffers)

Create a WebGLRenderbuffer object and initialize it with a renderbuffer object name as if by calling glGenRenderbuffers.

void deleteRenderbuffer(WebGLRenderbuffer? renderbuffer) (OpenGL ES 2.0 §4.4.3, similar to glDeleteRenderbuffers)

If renderbuffer was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Mark for deletion the renderbuffer object contained in the passed WebGLRenderbuffer, as if by calling glDeleteRenderbuffers. If the object has already been marked for deletion, the call has no effect. Note that underlying GL object will be automatically marked for deletion when the JS object is destroyed, however this method allows authors to mark an object for deletion early.

any getRenderbufferParameter(GLenum target, GLenum pname) (OpenGL ES 2.0 §6.1.3, similar to glGetRenderbufferParameteriv)

Return the value for the passed pname given the passed target. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
RENDERBUFFER_WIDTH	GLint
RENDERBUFFER_HEIGHT	GLint
RENDERBUFFER_INTERNAL_FORMAT	GLenum
RENDERBUFFER_RED_SIZE	GLint
RENDERBUFFER_GREEN_SIZE	GLint
RENDERBUFFER_BLUE_SIZE	GLint
RENDERBUFFER_ALPHA_SIZE	GLint
RENDERBUFFER_DEPTH_SIZE	GLint
RENDERBUFFER_STENCIL_SIZE	GLint

If pname is not in the table above, generates an INVALID_ENUM error.

If an OpenGL error is generated, returns null.

[WebGLHandlesContextLoss] GLboolean isRenderbuffer(WebGLRenderbuffer? renderbuffer) (OpenGL ES 2.0 §6.1.7, man page)

Return true if the passed WebGLRenderbuffer is valid and false otherwise.

Returns false if the renderbuffer was generated by a different WebGLRenderingContext than this one.

Returns false if the renderbuffer's invalidated flag is set.

void renderbufferStorage(GLenum target, GLenum internalformat, GLsizei width, GLsizei height) (OpenGL ES 2.0 §4.4.3, man page)

Texture objects

Texture objects provide storage and state for texturing operations. If no WebGLTexture is bound (e.g., passing null or 0 to bindTexture) then attempts to modify or query the texture object shall generate an INVALID_OPERATION error. This is indicated in the functions below.

void bindTexture(GLenum target, WebGLTexture? texture) (OpenGL ES 2.0 §3.7.13, man page)

If texture was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

An attempt to bind an object marked for deletion will generate an INVALID_OPERATION error, and the current binding will remain untouched.

void compressedTexImage2D(GLenum target, GLint level, GLenum internalformat, GLsizei width, GLsizei height, GLint border, [AllowShared] ArrayBufferView pixels) (OpenGL ES 2.0 §3.7.3, man page) void compressedTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, [AllowShared] ArrayBufferView pixels) (OpenGL ES 2.0 §3.7.3, man page)

If an attempt is made to call these functions with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

The core WebGL specification does not define any supported compressed texture formats. By default, these methods generate an INVALID_ENUM error and return immediately. See Compressed Texture Support.

void copyTexImage2D(GLenum target, GLint level, GLenum internalformat, GLint x, GLint y, GLsizei width, GLsizei height, GLint border) (OpenGL ES 2.0 §3.7.2, man page)

A [Read Operation].
If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

This function behaves as if texImage2D were called with null data, followed by copyTexSubImage2D. As in copyTexSubImage2D, for any source pixels lying outside the framebuffer, the corresponding destination texels are left untouched, and so they retain their zero-initialized contents as if texImage2D was called with null data. This has the combined effect that, for source pixels lying outside the framebuffer, corresponding destination pixels will have all channels of the associated texels initialized to 0; see Reading Pixels Outside the Framebuffer.

If this function attempts to read from a complete framebuffer with a missing attachment, an INVALID_OPERATION error is generated per Reading from a Missing Attachment.

void copyTexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLint x, GLint y, GLsizei width, GLsizei height) (OpenGL ES 2.0 §3.7.2, man page)

A [Read Operation].
If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

For any pixel lying outside the frame buffer, the corresponding destination pixel remains untouched; see Reading Pixels Outside the Framebuffer.

If this function attempts to read from a complete framebuffer with a missing attachment, an INVALID_OPERATION error is generated per Reading from a Missing Attachment.

WebGLTexture createTexture() (OpenGL ES 2.0 §3.7.13, man page)

Create a WebGLTexture object and initialize it with a texture object name as if by calling glGenTextures.

void deleteTexture(WebGLTexture? texture) (OpenGL ES 2.0 §3.7.13, man page)

If texture was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Mark for deletion the texture object contained in the passed WebGLTexture, as if by calling glDeleteTextures. If the object has already been marked for deletion, the call has no effect. Note that underlying GL object will be automatically marked for deletion when the JS object is destroyed, however this method allows authors to mark an object for deletion early.

void generateMipmap(GLenum target) (OpenGL ES 2.0 §3.7.11, man page)

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

any getTexParameter(GLenum target, GLenum pname) (OpenGL ES 2.0 §6.1.3, man page)

Return the value for the passed pname given the passed target. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
TEXTURE_MAG_FILTER	GLenum
TEXTURE_MIN_FILTER	GLenum
TEXTURE_WRAP_S	GLenum
TEXTURE_WRAP_T	GLenum

If pname is not in the table above, generates an INVALID_ENUM error.

If an attempt is made to call this function with no WebGLTexture bound (see above), generates an INVALID_OPERATION error.

If an OpenGL error is generated, returns null.

[WebGLHandlesContextLoss] GLboolean isTexture(WebGLTexture? texture) (OpenGL ES 2.0 §6.1.4, man page)

Return true if the passed WebGLTexture is valid and false otherwise.

Returns false if the texture was generated by a different WebGLRenderingContext than this one.

Returns false if the texture's invalidated flag is set.

void texImage2D(GLenum target, GLint level, GLint internalformat, GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, [AllowShared] ArrayBufferView? pixels) (OpenGL ES 2.0 §3.7.1, man page)

If pixels is null, a buffer of sufficient size initialized to 0 is passed.

If pixels is non-null, the type of pixels must match the type of the data to be read. If it is UNSIGNED_BYTE, a Uint8Array or Uint8ClampedArray must be supplied; if it is UNSIGNED_SHORT_5_6_5, UNSIGNED_SHORT_4_4_4_4, or UNSIGNED_SHORT_5_5_5_1, a Uint16Array must be supplied. If the types do not match, an INVALID_OPERATION error is generated.

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

See Pixel Storage Parameters for WebGL-specific pixel storage parameters that affect the behavior of this function.

If pixels is non-null but its size is less than what is required by the specified width, height, format, type, and pixel storage parameters, generates an INVALID_OPERATION error.

void texImage2D(GLenum target, GLint level, GLint internalformat, GLenum format, GLenum type, TexImageSource source) /* May throw DOMException */ (OpenGL ES 2.0 §3.7.1, man page)

Uploads the given element or image data to the currently bound WebGLTexture.

The width and height of the texture are set as specified in section Texture Upload Width and Height.

First, the source image data is conceptually converted to the color space specified by the unpackColorSpace attribute, except if the the UNPACK_COLORSPACE_CONVERSION_WEBGL pixel storage parameter is set to NONE.

This color space conversion applies to ImageBitmap objects as well, though other texture unpack parameters do not apply to ImageBitmaps because they are expected to be specified during ImageBitmap construction. Implementation experience revealed that it was beneficial to perform ImageBitmaps' color space conversion as late as possible when uploading to WebGL textures.

Next, the source image data is converted to the data type and format specified by the format and type arguments, and then transferred to the WebGL implementation. Format conversion is performed according to the following table. If a packed pixel format is specified which would imply loss of bits of precision from the image data, this loss of precision must occur.

Source DOM Image Format	Target WebGL Format
Source DOM Image Format	ALPHA	RGB	RGBA	LUMINANCE	LUMINANCE_ALPHA
Grayscale (1 channel)	A = 255 (1.0)	R = sourceGray G = sourceGray B = sourceGray	R = sourceGray G = sourceGray B = sourceGray A = 255 (1.0)	L = sourceGray	L = sourceGray A = 255 (1.0)
Grayscale + Alpha (2 channels)	A = sourceAlpha	R = sourceGray G = sourceGray B = sourceGray	R = sourceGray G = sourceGray B = sourceGray A = sourceAlpha	L = sourceGray	L = sourceGray A = sourceAlpha
Color (3 channels)	A = 255 (1.0)	R = sourceRed G = sourceGreen B = sourceBlue	R = sourceRed G = sourceGreen B = sourceBlue A = 255 (1.0)	L = sourceRed	L = sourceRed A = 255 (1.0)
Color + Alpha (4 channels)	A = sourceAlpha	R = sourceRed G = sourceGreen B = sourceBlue	R = sourceRed G = sourceGreen B = sourceBlue A = sourceAlpha	L = sourceRed	L = sourceRed A = sourceAlpha

See Pixel Storage Parameters for WebGL-specific pixel storage parameters that affect the behavior of this function when it is called with any argument type other than ImageBitmap.

The first pixel transferred from the source to the WebGL implementation corresponds to the upper left corner of the source. This behavior is modified by the UNPACK_FLIP_Y_WEBGL pixel storage parameter, except for ImageBitmap arguments, as described in the abovementioned section.

If the source is an HTMLImageElement or ImageBitmap containing an RGB or RGBA lossless image with 8 bits per channel, the browser guarantees that the full precision of all channels is preserved.

If the original HTMLImageElement contains an alpha channel and the UNPACK_PREMULTIPLY_ALPHA_WEBGL pixel storage parameter is false, then the RGB values are guaranteed to never have been premultiplied by the alpha channel, whether those values are derived directly from the original file format or converted from some other color format.

Some implementations of HTMLCanvasElement's or OffscreenCanvas's CanvasRenderingContext2D store color values internally in premultiplied form. If such a canvas is uploaded to a WebGL texture with the UNPACK_PREMULTIPLY_ALPHA_WEBGL pixel storage parameter set to false, the color channels will have to be un-multiplied by the alpha channel, which is a lossy operation. The WebGL implementation therefore can not guarantee that colors with alpha < 1.0 will be preserved losslessly when first drawn to a canvas via CanvasRenderingContext2D and then uploaded to a WebGL texture when the UNPACK_PREMULTIPLY_ALPHA_WEBGL pixel storage parameter is set to false.

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

If this function is called with an ImageData whose data attribute has been neutered, an INVALID_VALUE error is generated.

If this function is called with an ImageBitmap that has been neutered, an INVALID_VALUE error is generated.

If this function is called with an HTMLImageElement or HTMLVideoElement whose origin differs from the origin of the containing Document, or with an HTMLCanvasElement, ImageBitmap or OffscreenCanvas whose bitmap's origin-clean flag is set to false, a SECURITY_ERR exception must be thrown. See Origin Restrictions.

If source is null then an INVALID_VALUE error is generated.

void texParameterf(GLenum target, GLenum pname, GLfloat param) (OpenGL ES 2.0 §3.7.4, man page)

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

void texParameteri(GLenum target, GLenum pname, GLint param) (OpenGL ES 2.0 §3.7.4, man page)

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, GLenum type, [AllowShared] ArrayBufferView? pixels) (OpenGL ES 2.0 §3.7.2, man page)

See texImage2D for restrictions on the format and pixels arguments.

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

If type does not match the type originally used to define the texture, an INVALID_OPERATION error is generated.

If pixels is null then an INVALID_VALUE error is generated.

If pixels is non-null but its size is less than what is required by the specified width, height, format, type, and pixel storage parameters, generates an INVALID_OPERATION error.

See Pixel Storage Parameters for WebGL-specific pixel storage parameters that affect the behavior of this function.

void texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset, GLenum format, GLenum type, TexImageSource source) /* May throw DOMException */ (OpenGL ES 2.0 §3.7.2, man page)

Updates a sub-rectangle of the currently bound WebGLTexture with the contents of the given element or image data.

The width and height of the updated sub-rectangle are determined as specified in section Texture Upload Width and Height.

See texImage2D for the interpretation of the format and type arguments, handling of WebGL-specific pixel storage parameters, and potential color space transformations of the input.

The first pixel transferred from the source to the WebGL implementation corresponds to the upper left corner of the source. This behavior is modified by the UNPACK_FLIP_Y_WEBGL pixel storage parameter, except for ImageBitmap arguments, as described in the abovementioned section.

If an attempt is made to call this function with no WebGLTexture bound (see above), an INVALID_OPERATION error is generated.

If type does not match the type originally used to define the texture, an INVALID_OPERATION error is generated.

If this function is called with an ImageData whose data attribute has been neutered, an INVALID_VALUE error is generated.

If this function is called with an ImageBitmap that has been neutered, an INVALID_VALUE error is generated.

If this function is called with an HTMLImageElement or HTMLVideoElement whose origin differs from the origin of the containing Document, or with an HTMLCanvasElement, ImageBitmap, or OffscreenCanvas whose bitmap's origin-clean flag is set to false, a SECURITY_ERR exception must be thrown. See Origin Restrictions.

If source is null then an INVALID_VALUE error is generated.

Programs and Shaders

Rendering with OpenGL ES 2.0 requires the use of shaders, written in OpenGL ES's shading language, GLSL ES. Shaders must be loaded with a source string (shaderSource), compiled (compileShader) and attached to a program (attachShader) which must be linked (linkProgram) and then used (useProgram).

void attachShader(WebGLProgram program, WebGLShader shader) (OpenGL ES 2.0 §2.10.3, man page)

If either program or shader were generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

void bindAttribLocation(WebGLProgram program, GLuint index, DOMString name) (OpenGL ES 2.0 §2.10.4, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

If the passed name is longer than the restriction defined in Maximum Uniform and Attribute Location Lengths, generates an INVALID_VALUE error.

If name starts with one of the reserved WebGL prefixes per GLSL Constructs, generates an INVALID_OPERATION error.

See Characters Outside the GLSL Source Character Set for additional validation performed by WebGL implementations.

void compileShader(WebGLShader shader) (OpenGL ES 2.0 §2.10.1, man page)

If shader was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

See Supported GLSL Constructs, Maximum GLSL Token Size, Characters Outside the GLSL Source Character Set, Maximum Nesting of Structures in GLSL Shaders, and Packing Restrictions for Uniforms and Varyings for additional constraints enforced in, additional constructs supported by, and additional validation performed by WebGL implementations.

WebGLProgram createProgram() (OpenGL ES 2.0 §2.10.3, man page)

Create a WebGLProgram object and initialize it with a program object name as if by calling glCreateProgram.

WebGLShader? createShader(GLenum type) (OpenGL ES 2.0 §2.10.1, man page)

Create a WebGLShader object and initialize it with a shader object name as if by calling glCreateShader.

void deleteProgram(WebGLProgram? program) (OpenGL ES 2.0 §2.10.3, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Mark for deletion the program object contained in the passed WebGLProgram, as if by calling glDeleteProgram. If the object has already been marked for deletion, the call has no effect. Note that underlying GL object will be automatically marked for deletion when the JS object is destroyed, however this method allows authors to mark an object for deletion early.

void deleteShader(WebGLShader? shader) (OpenGL ES 2.0 §2.10.1, man page)

If shader was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Mark for deletion the shader object contained in the passed WebGLShader, as if by calling glDeleteShader. If the object has already been marked for deletion, the call has no effect. Note that underlying GL object will be automatically marked for deletion when the JS object is destroyed, however this method allows authors to mark an object for deletion early.

void detachShader(WebGLProgram program, WebGLShader shader) (OpenGL ES 2.0 §2.10.3, man page)

If either program or shader were generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

sequence<WebGLShader>? getAttachedShaders(WebGLProgram program) (OpenGL ES 2.0 §6.1.8, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Returns a new object representing the list of shaders attached to the passed program.

Returns null if any OpenGL errors are generated during the execution of this function.

any getProgramParameter(WebGLProgram program, GLenum pname) (OpenGL ES 2.0 §6.1.8, similar to man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Return the value for the passed pname given the passed program. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
DELETE_STATUS	GLboolean
LINK_STATUS	GLboolean
VALIDATE_STATUS	GLboolean
ATTACHED_SHADERS	GLint
ACTIVE_ATTRIBUTES	GLint
ACTIVE_UNIFORMS	GLint

If pname is not in the table above, generates an INVALID_ENUM error and returns null.

Returns null if any OpenGL errors are generated during the execution of this function.

DOMString? getProgramInfoLog(WebGLProgram program) (OpenGL ES 2.0 §6.1.8, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Returns null if any OpenGL errors are generated during the execution of this function.

any getShaderParameter(WebGLShader shader, GLenum pname) (OpenGL ES 2.0 §6.1.8, similar to man page)

If shader was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Return the value for the passed pname given the passed shader. The type returned is the natural type for the requested pname, as given in the following table:

pname	returned type
SHADER_TYPE	GLenum
DELETE_STATUS	GLboolean
COMPILE_STATUS	GLboolean

If pname is not in the table above, generates an INVALID_ENUM error and returns null.

Returns null if any OpenGL errors are generated during the execution of this function.

WebGLShaderPrecisionFormat? getShaderPrecisionFormat(GLenum shadertype, GLenum precisiontype) (OpenGL ES 2.0 §6.1.8, similar to man page)

Return a new WebGLShaderPrecisionFormat describing the range and precision for the specified shader numeric format. The shadertype value can be FRAGMENT_SHADER or VERTEX_SHADER. The precisiontype value can be LOW_FLOAT, MEDIUM_FLOAT, HIGH_FLOAT, LOW_INT, MEDIUM_INT or HIGH_INT.

Returns null if any OpenGL errors are generated during the execution of this function.

DOMString? getShaderInfoLog(WebGLShader shader) (OpenGL ES 2.0 §6.1.8, man page)

If shader was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Returns null if any OpenGL errors are generated during the execution of this function.

DOMString? getShaderSource(WebGLShader shader) (OpenGL ES 2.0 §6.1.8, man page)

If shader was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Returns null if any OpenGL errors are generated during the execution of this function.

[WebGLHandlesContextLoss] GLboolean isProgram(WebGLProgram? program) (OpenGL ES 2.0 §6.1.8, man page)

Return true if the passed WebGLProgram is valid and false otherwise.

Returns false if the program was generated by a different WebGLRenderingContext than this one.

Returns false if the program's invalidated flag is set.

[WebGLHandlesContextLoss] GLboolean isShader(WebGLShader? shader) (OpenGL ES 2.0 §6.1.8, man page)

Return true if the passed WebGLShader is valid and false otherwise.

Returns false if the shader was generated by a different WebGLRenderingContext than this one.

Returns false if the shader's invalidated flag is set.

void linkProgram(WebGLProgram program) (OpenGL ES 2.0 §2.10.3, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Links the passed program object. Details of the behavior are defined in the OpenGL ES 2.0 specification, with the following clarifications: linkProgram is the only API in this group which affects the passed program's link status, and the internal executable code it references. Operations like attaching and detaching shader objects from a program, modifying shader objects which are attached to a program, or compiling shader objects attached to a program affect neither that program's link status, nor the executable code that program may reference.

If the given program is also the the current program object in use as defined by useProgram, below, then:

If the program is linked successfully, the generated executable code is immediately installed as part of the current rendering state.
If the program is not linked successfully, the executable code referenced by the current rendering state is immediately invalidated. Further draw calls that utilize the current program generate an INVALID_OPERATION error. See Current program invalidated upon unsuccessful link.

See Packing Restrictions for Uniforms and Varyings for additional constraints enforced in, and additional validation performed by, WebGL implementations.

void shaderSource(WebGLShader shader, DOMString source) (OpenGL ES 2.0 §2.10.1, man page)

void useProgram(WebGLProgram? program) (OpenGL ES 2.0 §2.10.3, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

void validateProgram(WebGLProgram program) (OpenGL ES 2.0 §2.10.5, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Uniforms and attributes

Values used by the shaders are passed in as uniforms or vertex attributes.

void disableVertexAttribArray(GLuint index) (OpenGL ES 2.0 §2.8, man page)

void enableVertexAttribArray(GLuint index) (OpenGL ES 2.0 §2.8, man page)

Enable the vertex attribute at index as an array. WebGL imposes additional rules beyond OpenGL ES 2.0 regarding enabled vertex attributes; see Enabled Vertex Attributes and Range Checking.

WebGLActiveInfo? getActiveAttrib(WebGLProgram program, GLuint index) (OpenGL ES 2.0 §2.10.4, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Returns a new WebGLActiveInfo object describing the size, type and name of the vertex attribute at the passed index of the passed program object. If the passed index is out of range, generates an INVALID_VALUE error and returns null.

Returns null if any OpenGL errors are generated during the execution of this function.

WebGLActiveInfo? getActiveUniform(WebGLProgram program, GLuint index) (OpenGL ES 2.0 §2.10.4, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Returns a new WebGLActiveInfo object describing the size, type and name of the uniform at the passed index of the passed program object. If the passed index is out of range, generates an INVALID_VALUE error and returns null.

Returns null if any OpenGL errors are generated during the execution of this function.

[WebGLHandlesContextLoss] GLint getAttribLocation(WebGLProgram program, DOMString name) (OpenGL ES 2.0 §2.10.4, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error and returns -1.

If the passed name is longer than the restriction defined in Maximum Uniform and Attribute Location Lengths, generates an INVALID_VALUE error and returns -1.

Returns -1 if name starts with one of the reserved WebGL prefixes per GLSL Constructs.

Returns -1 if the context's webgl context lost flag is set.

If the invalidated flag of the passed program is set, generates an INVALID_OPERATION error and returns -1.

See Characters Outside the GLSL Source Character Set for additional validation performed by WebGL implementations.

any getUniform(WebGLProgram program, WebGLUniformLocation location) (OpenGL ES 2.0 §6.1.8, man page)

If either program or location were generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Return the uniform value at the passed location in the passed program. The type returned is dependent on the uniform type, as shown in the following table:

uniform type	returned type
boolean	GLboolean
int	GLint
float	GLfloat
vec2	Float32Array (with 2 elements)
ivec2	Int32Array (with 2 elements)
bvec2	sequence<GLboolean> (with 2 elements)
vec3	Float32Array (with 3 elements)
ivec3	Int32Array (with 3 elements)
bvec3	sequence<GLboolean> (with 3 elements)
vec4	Float32Array (with 4 elements)
ivec4	Int32Array (with 4 elements)
bvec4	sequence<GLboolean> (with 4 elements)
mat2	Float32Array (with 4 elements)
mat3	Float32Array (with 9 elements)
mat4	Float32Array (with 16 elements)
sampler2D	GLint
samplerCube	GLint

All queries returning sequences or typed arrays return a new object each time.

Returns null if any OpenGL errors are generated during the execution of this function.

WebGLUniformLocation? getUniformLocation(WebGLProgram program, DOMString name) (OpenGL ES 2.0 §2.10.4, man page)

If program was generated by a different WebGLRenderingContext than this one, generates an INVALID_OPERATION error.

Return a new WebGLUniformLocation that represents the location of a specific uniform variable within a program object. The return value is null if name does not correspond to an active uniform variable in the passed program.

If the passed name is longer than the restriction defined in Maximum Uniform and Attribute Location Lengths, generates an INVALID_VALUE error and returns null.

Returns null if name starts with one of the reserved WebGL prefixes per GLSL Constructs.

See Characters Outside the GLSL Source Character Set for additional validation performed by WebGL implementations.

Returns null if any OpenGL errors are generated during the execution of this function.

any getVertexAttrib(GLuint index, GLenum pname) (OpenGL ES 2.0 §6.1.8, man page)

Return the information requested in pname about the vertex attribute at the passed index. The type returned is dependent on the information requested, as shown in the following table:

pname	returned type
VERTEX_ATTRIB_ARRAY_BUFFER_BINDING	WebGLBuffer
VERTEX_ATTRIB_ARRAY_ENABLED	GLboolean
VERTEX_ATTRIB_ARRAY_SIZE	GLint
VERTEX_ATTRIB_ARRAY_STRIDE	GLint
VERTEX_ATTRIB_ARRAY_TYPE	GLenum
VERTEX_ATTRIB_ARRAY_NORMALIZED	GLboolean
CURRENT_VERTEX_ATTRIB	Float32Array (with 4 elements)

All queries returning sequences or typed arrays return a new object each time.

If pname is not in the table above, generates an INVALID_ENUM error.

If an OpenGL error is generated, returns null.

[WebGLHandlesContextLoss] GLsizeiptr getVertexAttribOffset(GLuint index, GLenum pname) (OpenGL ES 2.0 §6.1.8, similar to man page)

Returns 0 if the context's webgl context lost flag is set.

void uniform[1234][fi](WebGLUniformLocation? location, ...) void uniform[1234][fi]v(WebGLUniformLocation? location, ...) void uniformMatrix[234]fv(WebGLUniformLocation? location, GLboolean transpose, ...) (OpenGL ES 2.0 §2.10.4, man page)

Each of the uniform* functions above sets the specified uniform or uniforms to the values provided. If the passed location is not null and was not obtained from the currently used program via an earlier call to getUniformLocation, an INVALID_OPERATION error will be generated. If the passed location is null, the data passed in will be silently ignored and no uniform variables will be changed.

If the array passed to any of the vector forms (those ending in v) has an invalid length, an INVALID_VALUE error will be generated. The length is invalid if it is too short for or is not an integer multiple of the assigned type.

Performance problems have been observed on some implementations when using uniform1i to update sampler uniforms. To change the texture referenced by a sampler uniform, binding a new texture to the texture unit referenced by the uniform should be preferred over using uniform1i to update the uniform itself.

void vertexAttrib[1234]f(GLuint index, ...) void vertexAttrib[1234]fv(GLuint index, ...) (OpenGL ES 2.0 §2.7, man page)

Sets the vertex attribute at the passed index to the given constant value. Values set via the vertexAttrib are guaranteed to be returned from the getVertexAttrib function with the CURRENT_VERTEX_ATTRIB param, even if there have been intervening calls to drawArrays or drawElements.

If the array passed to any of the vector forms (those ending in v) is too short, an INVALID_VALUE error will be generated.

void vertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, GLintptr offset) (OpenGL ES 2.0 §2.8, man page)

Assign the WebGLBuffer object currently bound to the ARRAY_BUFFER target to the vertex attribute at the passed index. Size is number of components per attribute. Stride and offset are in units of bytes. Passed stride and offset must be appropriate for the passed type and size or an INVALID_OPERATION error will be generated; see Buffer Offset and Stride Requirements. If offset is negative, an INVALID_VALUE error will be generated. If no WebGLBuffer is bound to the ARRAY_BUFFER target and offset is non-zero, an INVALID_OPERATION error will be generated. In WebGL, the maximum supported stride is 255; see Vertex Attribute Data Stride.

Draw Operations

OpenGL ES 2.0 has several calls which are allowed to write to the currently bound (draw) framebuffer. WebGL categorizes all such calls as [Draw Operations].

Furthermore, rendering can be directed to the drawing buffer or to a Framebuffer object. When rendering is directed to the drawing buffer, making any of the rendering calls shall cause the drawing buffer to be presented to the HTML page compositor at the start of the next compositing operation.

These include, but (due to additions in extensions or in WebGL 2.0) are not limited to:

clear
drawArrays
drawElements

For instance, ANGLE_instanced_arrays adds drawArraysInstancedANGLE, and WebGL 2.0 adds drawArraysInstanced.

If any one of these calls attempts to draw to a missing attachment of a complete framebuffer, nothing is drawn to that attachment and no error is generated per Drawing to a Missing Attachment.

void clear(GLbitfield mask) (OpenGL ES 2.0 §4.2.3, man page): A [Draw Operation].
void drawArrays(GLenum mode, GLint first, GLsizei count) (OpenGL ES 2.0 §2.8, man page): A [Draw Operation].
If first is negative, an INVALID_VALUE error will be generated. If the CURRENT_PROGRAM is null, an INVALID_OPERATION error will be generated.
void drawElements(GLenum mode, GLsizei count, GLenum type, GLintptr offset) (OpenGL ES 2.0 §2.8, man page): A [Draw Operation].
Draw using the currently bound element array buffer. The given offset is in bytes, and must be a valid multiple of the size of the given type or an INVALID_OPERATION error will be generated; in addition the offset must be non-negative or an INVALID_VALUE error will be generated; see Buffer Offset and Stride Requirements. If count is greater than zero, then a non-null WebGLBuffer must be bound to the ELEMENT_ARRAY_BUFFER binding point or an INVALID_OPERATION error will be generated.

If the CURRENT_PROGRAM is null, an INVALID_OPERATION error will be generated.
WebGL performs additional error checking beyond that specified in OpenGL ES 2.0 during calls to drawArrays and drawElements. See Enabled Vertex Attributes and Range Checking.
void finish() (OpenGL ES 2.0 §5.1, man page)
void flush() (OpenGL ES 2.0 §5.1, man page)

Read Operations

OpenGL ES 2.0 has several calls which are allowed to read from the currently bound (read) framebuffer. WebGL categorizes all such calls as [Read Operations].

These include, but (due to additions in extensions or in WebGL 2.0) are not limited to:

copyTexImage2D
copyTexSubImage2D
readPixels

void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, [AllowShared] ArrayBufferView? pixels) (OpenGL ES 2.0 §4.3.1, man page): A [Read Operation].
Pixels in the current framebuffer are read back into an ArrayBufferView object.
Fills pixels with the pixel data in the specified rectangle of the frame buffer. The data returned from readPixels must be up-to-date as of the most recently sent drawing command.

The type of pixels must match the type of the data to be read. For example, if it is UNSIGNED_BYTE, a Uint8Array or Uint8ClampedArray must be supplied; if it is UNSIGNED_SHORT_5_6_5, UNSIGNED_SHORT_4_4_4_4, or UNSIGNED_SHORT_5_5_5_1, a Uint16Array must be supplied; if it is FLOAT, a Float32Array must be supplied. If the types do not match, an INVALID_OPERATION error is generated.

Only two combinations of format and type are accepted. The first is format RGBA and type UNSIGNED_BYTE. The second is an implementation-chosen format. The values of format and type for this format may be determined by calling getParameter with the symbolic constants IMPLEMENTATION_COLOR_READ_FORMAT and IMPLEMENTATION_COLOR_READ_TYPE, respectively. The implementation-chosen format may vary depending on the format of the currently bound rendering surface. Unsupported combinations of format and type will generate an INVALID_OPERATION error.

Because queries of IMPLEMENTATION_COLOR_READ_[FORMAT,TYPE] may return enums not used elsewhere, providing these enums to readPixels will not necessarily generate INVALID_ENUM.

If pixels is null, an INVALID_VALUE error is generated. If pixels is non-null, but is not large enough to retrieve all of the pixels in the specified rectangle taking into account pixel store modes, an INVALID_OPERATION error is generated.

For any pixel lying outside the frame buffer, the corresponding destination buffer range remains untouched; see Reading Pixels Outside the Framebuffer.

If this function attempts to read from a complete framebuffer with a missing color attachment, an INVALID_OPERATION error is generated per Reading from a Missing Attachment.

Detecting context lost events

Occurrences such as power events on mobile devices may cause the WebGL rendering context to be lost at any time and require the application to rebuild it; see WebGLContextEvent for more details. The following method assists in detecting context lost events.

[WebGLHandlesContextLoss] boolean isContextLost(): Return true if the webgl context lost flag is set, otherwise return false.

Detecting and enabling extensions

An implementation of WebGL must not support any additional parameters, constants or functions without first enabling that functionality through the extension mechanism. The getSupportedExtensions function returns an array of the extension strings supported by this implementation. An extension is enabled by passing one of those strings to the getExtension function. This call returns an object which contains any constants or functions defined by that extension. The definition of that object is specific to the extension and must be defined by the extension specification.

Once an extension is enabled, it is only disabled if the WebGL rendering context is lost (see below), with the exception of the "WEBGL_lose_context" extension which remains active through any loss of context. Any objects referenced by a disabled extension, such as the object returned by getExtension, are no longer associated with the WebGL rendering context. Any extension objects that derive from WebGLObject have their invalidated flag set to true. Behavior of extensions' methods after context loss is defined by the steps in the section "The WebGL context".

There are no other mechanisms to disable an extension.

Multiple calls to getExtension with the same extension string, taking into account case-insensitive comparison, must return the same object as long as the extension is enabled. An attempt to use any features of an extension without first calling getExtension to enable it must generate an appropriate GL error and must not make use of the feature.

This specification does not define any extensions. A separate WebGL extension registry defines extensions that may be supported by a particular WebGL implementation.

sequence<DOMString>? getSupportedExtensions(): Returns a list of all the supported extension strings.
object? getExtension(DOMString name): Returns an object if, and only if, name is an ASCII case-insensitive match [HTML] for one of the names returned from getSupportedExtensions; otherwise, returns null. The object returned from getExtension contains any constants or functions provided by the extension. A returned object may have no constants or functions if the extension does not define any, but a unique object must still be returned. That object is used to indicate that the extension has been enabled.

WebGLContextEvent

WebGL generates a WebGLContextEvent event in response to important changes in status of a WebGL rendering context. Events are sent using the DOM Event System [DOM3EVENTS], and are dispatched to the HTMLCanvasElement or OffscreenCanvas associated with the WebGL rendering context. The types of status changes that can trigger a WebGLContextEvent event are the loss of the context, the restoration of the context, and the inability to create a context.

To fire a WebGL context event named e means that an event using the WebGLContextEvent interface, with its type attribute [DOM4] initialized to e, its cancelable attribute initialized to true, and its isTrusted attribute [DOM4] initialized to true, is to be dispatched at the given object.

[Exposed=(Window,Worker)]
interface WebGLContextEvent : Event {
    constructor(DOMString type, optional WebGLContextEventInit eventInit = {});
    readonly attribute DOMString statusMessage;
};

// EventInit is defined in the DOM4 specification.
dictionary WebGLContextEventInit : EventInit {
    DOMString statusMessage = "";
};

The task source for all tasks queued [HTML] in this section is the WebGL task source.

Attributes

The following attributes are available:

statusMessage of type DOMString: A string containing additional information, or the empty string if no additional information is available.

The Context Lost Event

When the user agent detects that the drawing buffer associated with a WebGLRenderingContext context has been lost, it must run the following steps:

Let canvas be the context's canvas.
If context's webgl context lost flag is set, abort these steps.
Set context's webgl context lost flag.
Set the invalidated flag of each WebGLObject instance created by this context.
Disable all extensions except "WEBGL_lose_context".
Queue a task to perform the following steps:
1. Fire a WebGL context event named "webglcontextlost" at canvas, with its statusMessage attribute set to "".
2. If the event's canceled flag is not set, abort these steps.
3. Perform the following steps asynchronously.
4. Await a restorable drawing buffer.
5. Queue a task to restore the drawing buffer for context.

A WebGLObject created while the context is lost (e.g. a WebGLBuffer via createBuffer()) begins life with its invalidated flag set.

The following code prevents the default behavior of the webglcontextlost event and enables the webglcontextrestored event to be delivered:

canvas.addEventListener("webglcontextlost", function(e) { e.preventDefault(); }, false);

The Context Restored Event

When the user agent is to restore the drawing buffer for a WebGLRenderingContext context, it must run the following steps:

Let canvas be the canvas object associated with context.
If context's webgl context lost flag is not set, abort these steps.
Create a drawing buffer using the settings specified in context's context creation parameters, and associate the drawing buffer with context, discarding any previous drawing buffer.
Clear context's webgl context lost flag.
Reset context's OpenGL error state.
Fire a WebGL context event named "webglcontextrestored" at canvas, with its statusMessage attribute set to "".

Once the context is restored, WebGL resources such as textures and buffers that were created before the context was restored are no longer valid. Previously enabled extensions are not restored. The application will want to restore all modified state and destroyed extensions and resources.

The following code illustrates how an application can handle context loss and restoration:

function initializeGame() {
  initializeWorld();
  initializeResources();
}

function initializeResources() {
  initializeShaders();
  initializeBuffers();
  initializeTextures();

  // ready to draw, start the main loop
  renderFrame();
}

function renderFrame() {
  updateWorld();
  drawSkyBox();
  drawWalls();
  drawMonsters();

  requestId = window.requestAnimationFrame(
      renderFrame, canvas);
}

canvas.addEventListener(
    "webglcontextlost", function (event) {

  // inform WebGL that we handle context restoration
  event.preventDefault();

  // Stop rendering
  window.cancelAnimationFrame(requestId);
}, false);

canvas.addEventListener(
    "webglcontextrestored", function (event) {

  initializeResources();
}, false);

initializeGame();

The Context Creation Error Event

When the user agent is to fire a WebGL context creation error at a canvas, it must perform the following steps:

Fire a WebGL context event named "webglcontextcreationerror" at canvas, optionally with its statusMessage attribute set to a platform dependent string about the nature of the failure.

The following code illustrates how an application can retrieve information about context creation failure:

var errorInfo = "";
function onContextCreationError(event) {

  canvas.removeEventListener(
     "webglcontextcreationerror",
     onContextCreationError, false);

  errorInfo = e.statusMessage || "Unknown";
}

canvas.addEventListener(
    "webglcontextcreationerror",
    onContextCreationError, false);

var gl = canvas.getContext("webgl");
if(!gl) {
  alert("A WebGL context could not be created.\nReason: " +
        errorInfo);
}

Differences Between WebGL and OpenGL ES 2.0

This section describes changes made to the WebGL API relative to the OpenGL ES 2.0 API to improve portability across various operating systems and devices.

Buffer Object Binding

In the WebGL API, a given buffer object may only be bound to one of the ARRAY_BUFFER or ELEMENT_ARRAY_BUFFER binding points in its lifetime. This restriction implies that a given buffer object may contain either vertices or indices, but not both.

The type of a WebGLBuffer is initialized the first time it is passed as an argument to bindBuffer. A subsequent call to bindBuffer which attempts to bind the same WebGLBuffer to the other binding point will generate an INVALID_OPERATION error, and the state of the binding point will remain untouched.

No Client Side Arrays

The WebGL API does not support client-side arrays.

If a vertex attribute is enabled as an array via enableVertexAttribArray but no buffer is bound to that attribute (generally via bindBuffer and vertexAttribPointer), then draw commands (drawArrays or drawElements) will generate an INVALID_OPERATION error.

If an indexed draw command (drawElements) is called and no WebGLBuffer is bound to the ELEMENT_ARRAY_BUFFER binding point, an INVALID_OPERATION error is generated.

If vertexAttribPointer is called without a WebGLBuffer bound to the ARRAY_BUFFER binding point, and offset is non-zero, an INVALID_OPERATION error is generated.

Allowing setting VERTEX_ATTRIB_ARRAY_BUFFER_BINDING to null even though client-side arrays are never supported allows for clearing the binding to its original state, which isn't strictly possible otherwise.

This also matches the behavior in OpenGL ES 3.0.5 [GLES30] p25 for non-default VAO objects.

No Default Textures

The WebGL API does not support default textures. A non-null WebGLTexture object must be bound in order for texture-related operations and queries to succeed.

No Shader Binaries

Accessing binary representations of compiled shaders is not supported in the WebGL API. This includes the OpenGL ES 2.0 ShaderBinary entry point. In addition, querying shader binary formats and the availability of a shader compiler via getParameter is not supported in the WebGL API.

All WebGL implementations must implicitly support an on-line shader compiler.

Buffer Offset and Stride Requirements

The offset arguments to drawElements and vertexAttribPointer, and the stride argument to vertexAttribPointer, must be a multiple of the size of the data type passed to the call, or an INVALID_OPERATION error is generated.

This enforces the following requirement from OpenGL ES 2.0.25 [GLES20] p24:

"Clients must align data elements consistent with the requirements of the client platform, with an additional base-level requirement that an offset within a buffer to a datum comprising N basic machine units be a multiple of N."

In addition the offset argument to drawElements must be non-negative or an INVALID_VALUE error is generated.

Enabled Vertex Attributes and Range Checking

It is possible for draw commands to request data outside the bounds of a WebGLBuffer by calling a drawing command that requires fetching data for an active vertex attribute, when it is enabled as an array, either directly (drawArrays), or indirectly from an indexed draw (drawElements). If this occurs, then one of the following behaviors will result:

The WebGL implementation may generate an INVALID_OPERATION error and draw no geometry.
Out-of-range vertex fetches may return any of the following values:
- Values from anywhere within the buffer object.
- Zero values, or (0,0,0,x) vectors for vector reads where x is a valid value represented in the type of the vector components and may be any of:
  - 0, 1, or the maximum representable positive integer value, for signed or unsigned integer components
  - 0.0 or 1.0, for floating-point components

This behavior replicates that defined in [KHRROBUSTACCESS].

If a vertex attribute is enabled as an array, a buffer is bound to that attribute, but the attribute is not consumed by the current program, then regardless of the size of the bound buffer, it will not cause any error to be generated during a call to drawArrays or drawElements.

Out-of-bounds fetches from the index buffer

Calling an indexed drawing command (drawElements) that fetches index elements outside the bounds of ELEMENT_ARRAY_BUFFER will result in an INVALID_OPERATION error.

Framebuffer Object Attachments

WebGL adds the DEPTH_STENCIL_ATTACHMENT framebuffer object attachment point and the DEPTH_STENCIL renderbuffer internal format. To attach both depth and stencil buffers to a framebuffer object, call renderbufferStorage with the DEPTH_STENCIL internal format, and then call framebufferRenderbuffer with the DEPTH_STENCIL_ATTACHMENT attachment point.

A renderbuffer attached to the DEPTH_ATTACHMENT attachment point must be allocated with the DEPTH_COMPONENT16 internal format. A renderbuffer attached to the STENCIL_ATTACHMENT attachment point must be allocated with the STENCIL_INDEX8 internal format. A renderbuffer attached to the DEPTH_STENCIL_ATTACHMENT attachment point must be allocated with the DEPTH_STENCIL internal format.

In the WebGL API, it is an error to concurrently attach renderbuffers to the following combinations of attachment points:

DEPTH_ATTACHMENT + DEPTH_STENCIL_ATTACHMENT
STENCIL_ATTACHMENT + DEPTH_STENCIL_ATTACHMENT
DEPTH_ATTACHMENT + STENCIL_ATTACHMENT

If any of the constraints above are violated, then:

checkFramebufferStatus must return FRAMEBUFFER_UNSUPPORTED.
[Draw Operations] and [Read Operations], which either draw to or read from the framebuffer, must generate an INVALID_FRAMEBUFFER_OPERATION error and return early, leaving the contents of the framebuffer, destination texture or destination memory untouched.

The following combinations of framebuffer object attachments, when all of the attachments are framebuffer attachment complete, non-zero, and have the same width and height, must result in the framebuffer being framebuffer complete:

COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture
COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_ATTACHMENT = DEPTH_COMPONENT16 renderbuffer
COLOR_ATTACHMENT0 = RGBA/UNSIGNED_BYTE texture + DEPTH_STENCIL_ATTACHMENT = DEPTH_STENCIL renderbuffer

Texture Upload Width and Height

Unless width and height parameters are explicitly specified, the width and height of the texture set by texImage2D and the width and height of the sub-rectangle updated by texSubImage2D are determined based on the uploaded TexImageSource source object:

source of type ImageData: The width and height of the texture are set to the current values of the width and height properties of the ImageData object, representing the actual pixel width and height of the ImageData object.
source of type HTMLImageElement: If a bitmap is uploaded, the width and height of the texture are set to the width and height of the uploaded bitmap in pixels. If an SVG image is uploaded, the width and height of the texture are set to the current values of the width and height properties of the HTMLImageElement object.
source of type HTMLCanvasElement or OffscreenCanvas: The width and height of the texture are set to the current values of the width and height properties of the HTMLCanvasElement or OffscreenCanvas object.
source of type HTMLVideoElement or VideoFrame[WEBCODECS]: The width and height of the texture are set to the width and height of the uploaded frame of the video in pixels.

Pixel Storage Parameters

The WebGL API supports the following additional parameters to pixelStorei.

UNPACK_FLIP_Y_WEBGL of type boolean: If set, then during any subsequent calls to texImage2D or texSubImage2D, the source data is flipped along the vertical axis, so that conceptually the last row is the first one transferred. The initial value is false. Any non-zero value is interpreted as true.
UNPACK_PREMULTIPLY_ALPHA_WEBGL of type boolean: If set, then during any subsequent calls to texImage2D or texSubImage2D, the alpha channel of the source data, if present, is multiplied into the color channels during the data transfer. The initial value is false. Any non-zero value is interpreted as true.
UNPACK_COLORSPACE_CONVERSION_WEBGL of type unsigned long: If set to BROWSER_DEFAULT_WEBGL, then the browser's default colorspace conversion (e.g. converting a display-p3 image to srgb) is applied during subsequent texture data upload calls (e.g. texImage2D and texSubImage2D) that take an argument of TexImageSource. The precise conversions may be specific to both the browser and file type. If set to NONE, no colorspace conversion is applied, other than conversion to RGBA. (For example, a rec709 YUV video is still converted to rec709 RGB data, but not then converted to e.g. srgb RGB data) The initial value is BROWSER_DEFAULT_WEBGL.

If the TexImageSource is an ImageBitmap, then these three parameters will be ignored. Instead the equivalent ImageBitmapOptions should be used to create an ImageBitmap with the desired format.

Reading Pixels Outside the Framebuffer

For [Read Operations], reads from out-of-bounds pixels sub-areas do not touch their corresponding destination sub-areas.

WebGL (behaves as if it) pre-initializes resources to zeros. Therefore for example copyTexImage2D will have zeros in sub-areas that correspond to out-of-bounds framebuffer reads.

Stencil Separate Mask and Reference Value

In the WebGL API, if stencil testing is enabled and the currently bound framebuffer has a stencil buffer, then it is illegal to draw while any of the following cases are true. Doing so will generate an INVALID_OPERATION error.

(STENCIL_WRITEMASK & maxStencilValue) != (STENCIL_BACK_WRITEMASK & maxStencilValue)
(as specified by stencilMaskSeparate for the mask parameter associated with the FRONT and BACK values of face, respectively)
(STENCIL_VALUE_MASK & maxStencilValue) != (STENCIL_BACK_VALUE_MASK & maxStencilValue)
(as specified by stencilFuncSeparate for the mask parameter associated with the FRONT and BACK values of face, respectively)
clamp(STENCIL_REF, 0, maxStencilValue) != clamp(STENCIL_BACK_REF, 0, maxStencilValue)
(as specified by stencilFuncSeparate for the ref parameter associated with the FRONT and BACK values of face, respectively)

where maxStencilValue is ((1 << s) - 1), where s is the number of stencil bits in the draw framebuffer. (When no stencil bits are present, these checks always pass.)

Vertex Attribute Data Stride

The WebGL API supports vertex attribute data strides up to 255 bytes. A call to vertexAttribPointer will generate an INVALID_VALUE error if the value for the stride parameter exceeds 255.

Viewport Depth Range

The WebGL API does not support depth ranges with where the near plane is mapped to a value greater than that of the far plane. A call to depthRange will generate an INVALID_OPERATION error if zNear is greater than zFar.

Blending With Constant Color

In the WebGL API, constant color and constant alpha cannot be used together as source and destination factors in the blend function. A call to blendFunc will generate an INVALID_OPERATION error if one of the two factors is set to CONSTANT_COLOR or ONE_MINUS_CONSTANT_COLOR and the other to CONSTANT_ALPHA or ONE_MINUS_CONSTANT_ALPHA. A call to blendFuncSeparate will generate an INVALID_OPERATION error if srcRGB is set to CONSTANT_COLOR or ONE_MINUS_CONSTANT_COLOR and dstRGB is set to CONSTANT_ALPHA or ONE_MINUS_CONSTANT_ALPHA or vice versa.

Fixed point support

The WebGL API does not support the GL_FIXED data type.

GLSL Constructs

Per Supported GLSL Constructs, identifiers starting with "webgl_" and "_webgl_" are reserved for use by WebGL.

Extension Queries

In the OpenGL ES 2.0 API, the available extensions are determined by calling glGetString(GL_EXTENSIONS), which returns a space-separated list of extension strings. In the WebGL API, the EXTENSIONS enumerant has been removed. Instead, getSupportedExtensions must be called to determine the set of available extensions.

Compressed Texture Support

The core WebGL specification does not define any supported compressed texture formats. Therefore, in the absence of any other extensions being enabled:

The compressedTexImage2D and compressedTexSubImage2D methods generate an INVALID_ENUM error.
Calling getParameter with the argument COMPRESSED_TEXTURE_FORMATS returns a zero-length array (of type Uint32Array).

WebGL implementations should only expose compressed texture formats that are more efficient than the uncompressed form.

Maximum GLSL Token Size

The GLSL ES spec [GLES20GLSL] does not define a limit to the length of tokens. WebGL requires support of tokens up to 256 characters in length. Shaders containing tokens longer than 256 characters must fail to compile.

Characters Outside the GLSL Source Character Set

WebGL supports passing any HTML DOMString [DOMSTRING] to shaderSource without error. However during shader compilation, after GLSL preprocessing and comment stripping, all remaining characters MUST be within the character set of [GLES20GLSL]. Otherwise, the shader MUST fail to compile.

In particular, this allows for:

Non-ASCII unicode in comments
```
// 你好
```
Invalid characters in preprocessor-eliminated blocks
```
#ifdef __cplusplus
#line 42 "foo.glsl"
#endif
```
(The double-quote character is outside the GLSL character set, but since it is removed by preprocessing, this is allowed in shader sources)

The GLSL ES spec [GLES20GLSL] defines the source character set for the OpenGL ES shading language as a subset of ISO/IEC 646:1991, commonly called ASCII [ASCII]. Some GLSL implementations disallow any characters outside the ASCII range, even in comments. While browsers MUST correctly handle preprocessing the full DOMString character set, WebGL implementations generally must ensure that the shader source sent to a GLSL driver only contains ASCII for safety. Implementations SHOULD preserve line numbers for debugging purposes, potentially by inserting blank lines as needed.

If a string containing a character not in this set is passed to any of the other shader-related entry points bindAttribLocation, getAttribLocation, or getUniformLocation, an INVALID_VALUE error will be generated.

Maximum Nesting of Structures in GLSL Shaders

WebGL imposes a limit on the nesting of structures in GLSL shaders. Nesting occurs when a field in a struct refers to another struct type; the GLSL ES spec [GLES20GLSL] forbids embedded structure definitions. The fields in a top-level struct definition have a nesting level of 1.

WebGL requires support of a structure nesting level of 4. Shaders containing structures nested more than 4 levels deep must fail to compile.

Maximum Uniform and Attribute Location Lengths

WebGL imposes a limit of 256 characters on the lengths of uniform and attribute locations.

String Length Queries

In the WebGL API, the enumerants INFO_LOG_LENGTH, SHADER_SOURCE_LENGTH, ACTIVE_UNIFORM_MAX_LENGTH, and ACTIVE_ATTRIBUTE_MAX_LENGTH have been removed. In the OpenGL ES 2.0 API, these enumerants are needed to determine the size of buffers passed to calls like glGetActiveAttrib. In the WebGL API, the analogous calls (getActiveAttrib, getActiveUniform, getProgramInfoLog, getShaderInfoLog, and getShaderSource) all return DOMString.

Texture Type in TexSubImage2D Calls

In the WebGL API, the type argument passed to texSubImage2D must match the type used to originally define the texture object (i.e., using texImage2D).

Packing Restrictions for Uniforms and Varyings

The OpenGL ES Shading Language, Version 1.00 [GLES20GLSL], Appendix A, Section 7 "Counting of Varyings and Uniforms" defines a conservative algorithm for computing the storage required for all of the uniform and varying variables in a shader. The GLSL ES specification requires that if the packing algorithm defined in Appendix A succeeds, then the shader must succeed compilation on the target platform. The WebGL API further requires that if the packing algorithm fails either for the uniform variables of a shader or for the varying variables of a program, compilation or linking must fail.

Instead of using a fixed size grid of registers, the number of rows in the target architecture is determined in the following ways:

when counting uniform variables in a vertex shader: getParameter(MAX_VERTEX_UNIFORM_VECTORS)
when counting uniform variables in a fragment shader: getParameter(MAX_FRAGMENT_UNIFORM_VECTORS)
when counting varying variables: getParameter(MAX_VARYING_VECTORS)

The text above defines the circumstances under which compilation or linking of a shader or program must fail due to the constraints enforced by the packing algorithm. It is not guaranteed that a shader which uses more variables than the minimum required amount whose variables pack successfully according to this algorithm will compile successfully. Inefficiencies have been observed in implementations, including expansion of scalar arrays to consume multiple columns. Developers should avoid relying heavily upon automatic packing of multiple variables into columns. Instead, define larger variables (like vec4) and explicitly pack values into the rightmost columns.

Feedback Loops Between Textures and the Framebuffer

In the OpenGL ES 2.0 API, it's possible to make calls that both write to and read from the same texture, creating a feedback loop. It specifies that where these feedback loops exist, undefined behavior results.

In the WebGL API, such operations that would cause such feedback loops (by the definitions in the OpenGL ES 2.0 spec) will instead generate an INVALID_OPERATION error.

Reading From a Missing Attachment

In the OpenGL ES 2.0 API, it is not specified what happens when a command tries to source data from a missing attachment, such as ReadPixels of color data from a complete framebuffer that does not have a color attachment.

In the WebGL API, any [Read Operations] that require data from an attachment that is missing will generate an INVALID_OPERATION error.

Drawing To a Missing Attachment

In the OpenGL ES 2.0 API, it is not specified what happens when a command tries to draw to a missing attachment, such as clearing a draw buffer from a complete framebuffer that does not have a color attachment.

In the WebGL API, any [Draw Operations] that draw to an attachment that is missing will draw nothing to that attachment. No error is generated.

NaN Line Width

In the WebGL API, if the width parameter passed to lineWidth is set to NaN, an INVALID_VALUE error is generated and the line width is not changed.

Attribute Aliasing

It is possible for an application to bind more than one attribute name to the same location. This is referred to as aliasing. When more than one attributes that are aliased to the same location are active in the executable program, linkProgram should fail.

Initial value for gl_Position

The GLSL ES [GLES20GLSL] spec leaves the value of gl_Position as undefined unless it is written to in a vertex shader. WebGL guarantees that gl_Position's initial value is (0,0,0,0).

GLSL ES Global Variable Initialization

The GLSL ES 1.00 [GLES20GLSL] spec restricts global variable initializers to be constant expressions. In the WebGL API, it is allowed to use other global variables not qualified with the const qualifier and uniform values in global variable initializers in GLSL ES 1.00 shaders. Global variable initializers must be global initializer expressions, which are defined as one of:

a constant expression
a user-defined global variable
a uniform
an expression formed by an operator on operands that are global initializer expressions, including getting an element of a global initializer vector or global initializer matrix, or a field of a global initializer structure
a constructor whose arguments are all global initializer expressions
a built-in function call whose arguments are all global initializer expressions, with the exception of the texture lookup functions

The following may not be used in global initializer expressions:

User-defined functions
Attributes and varyings
Built-in variables with the exception of constant expressions
Global variables as l-values in an assignment or other operation

Compilers should generate a warning when a global variable initializer is in violation of the unmodified GLSL ES spec i.e. when a global variable initializer is not a constant expression.

This behavior has existed in WebGL implementations for several years. Fixing this behavior to be consistent with the GLSL ES specification would have a large compatibility impact with existing content.

GLSL ES Preprocessor "defined" Operator

The C++ standard, which the GLSL ES preprocessor specification refers to, has undefined behavior when the defined operator is generated by macro replacement when parsing the controlling expression of an #if or #elif directive. When shader code processed by the WebGL API generates the token defined during macro replacement inside a preprocessor expression, that must result in a compiler error.

This has no effect on macro expansion outside preprocessor directives that handle the defined operator.

Using defined as a macro name also has undefined behavior in the C++ standard. In the WebGL API, using defined as a macro name must result in a compiler error.

Behavior of the WebGL API should be consistent in cases where the native API spec allows undefined behavior.

GLSL ES #extension directive location

The GLSL ES 1.00 [GLES20GLSL] specification mandates that #extension directives must occur before any non-preprocessor tokens unless the extension specification says otherwise. In the WebGL API, #extension directives may always occur after non-preprocessor tokens in GLSL ES 1.00 shaders. The scope of #extension directives in GLSL ES 1.00 shaders is always the whole shader, and #extension directives that occur later override those seen earlier for the whole shader.

Letting extensions determine where the #extension directives should be placed has resulted in a lot of room for interpretation in the spec. In practice GLES implementations have not enforced the rule that's written in the GLSL ES spec, and neither have WebGL implementations, so relaxing the rule is the only way to make the spec well-defined while being compatible with existing content.

Completeness of Cube Map Framebuffer Attachments

In the WebGL API, a face of a cube map that is not cube complete is not framebuffer attachment complete. Querying framebuffer status when a face of an incomplete cube map is attached must return FRAMEBUFFER_INCOMPLETE_ATTACHMENT.

APIs that WebGL is implemented on, including recent OpenGL core versions and OpenGL ES 3.0 and newer, have a requirement that cube map faces used as a framebuffer attachment must be part of a cube complete cube map. See for example OpenGL ES 3.0.4 §4.4.4 "Framebuffer Completeness", subsection "Framebuffer Attachment Completeness".

Transferring vertices when current program is null

Any command that transfers vertices to the GL generates INVALID_OPERATION if the CURRENT_PROGRAM is null. This includes drawElements and drawArrays.

Fragment shader output

If a fragment shader writes to neither gl_FragColor nor gl_FragData, the values of the fragment colors following shader execution are untouched.

Initial values for GLSL local and global variables

The GLSL ES [GLES20GLSL] spec leaves the value of local and global variables as undefined unless they are initialized by the shader. WebGL guarantees that such variables are initialized to zero: 0.0, vec4(0.0), 0, false, etc.

Vertex attribute conversions from normalized signed integers to floating point

The OpenGL ES 2.0 spec [GLES20] section 2.1.2 "Data Conversions", subsection "Conversion from Integer to Floating-Point" defines conversion from a normalized signed integer c, where the bit width of the type is b, to floating-point value f as:

f = (2*c + 1) / (2^b - 1)

During conversions of signed normalized vertex attributes to floating point, WebGL 1.0 implementations may optionally use this conversion rule, which preserves zeros:

f = max(c / (2^(b - 1) - 1), -1.0)

Some APIs on which WebGL 1.0 is built on use the second rule, and since this conversion is done in fixed-function hardware, it is not possible to emulate one behavior or the other. This difference in behavior does not affect most applications, so a query to determine which behavior is being used has not been added to the WebGL rendering context.

Uniform and attribute name collisions

If any of the shaders attached to a WebGL program declare a uniform that has the same name as a statically used vertex attribute, program linking should fail.

This behavior differs from one specified in GLSL ES 3.00.6 section 12.47.

WebGL implementations have enforced this behavior for several years now, due to that some OpenGL drivers don't accept uniforms and vertex attributes with the same name.

Wide point primitive clipping

POINTS primitives may or may not be discarded if the vertex lies outside the clip volume, but within the near and far clip planes.

Clipping of wide points works differently in GLES and GL, and this difference in behavior is prohibitive to work around in implementations.

OpenGL ES 2.0.25 p46:

If the primitive under consideration is a point, then clipping discards it if it lies outside the near or far clip plane; otherwise it is passed unchanged.

OpenGL 3.2 Core p97:

If the primitive under consideration is a point, then clipping passes it unchanged if it lies within the clip volume; otherwise, it is discarded.

Current program invalidated upon unsuccessful link

In the WebGL API, if the program passed to linkProgram is also the current program object in use as defined by useProgram, and the link is unsuccessful, then the executable code referenced by the current rendering state is immediately invalidated. Further draw calls that utilize the current program generate an INVALID_OPERATION error.

Rejecting draw calls eagerly against programs whose relink has failed makes WebGL implementations more robust. The OpenGL ES API's behavior is that the current executable is preserved until the current program is changed. Correctly implementing this behavior in all scenarios is challenging, and has led to security bugs.

References

[CANVAS]: HTML5: The Canvas Element, World Wide Web Consortium (W3C).
[OFFSCREENCANVAS]: HTML Living Standard - The OffscreenCanvas interface, WHATWG.
[CANVASCONTEXTS]: Canvas Context Registry, WHATWG.
[ECMASCRIPT]: ECMAScript® 2015 Language Specification, Ecma International, 2015.
[GL32CORE]: The OpenGL® Graphics System: A Specification (Version 3.2 (Core Profile) - December 7, 2009), M. Segal, K. Akeley, December 2009.
[GLES20]: OpenGL® ES Common Profile Specification Version 2.0.25, A. Munshi, J. Leech, November 2010.
[GLES20GLSL]: The OpenGL® ES Shading Language Version 1.00, R. Simpson, May 2009.
[REGISTRY]: WebGL Extension Registry
[RFC2119]: Key words for use in RFCs to Indicate Requirement Levels, S. Bradner. IETF, March 1997.
[CSS]: Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification, B. Bos, T. Celik, I. Hickson, H. W. Lie, June 2011.
[CORS]: Cross-Origin Resource Sharing, A. van Kesteren, July 2010.
[DOM4]: DOM4, A. van Kesteren, A. Gregor, Ms2ger.
[DOM3EVENTS]: Document Object Model (DOM) Level 3 Events Specification, Doug Schepers and Jacob Rossi. W3C.
[HTML]: HTML, I. Hickson, June 2011.
[WEBIDL]: Web IDL - Living Standard, E. Chen, T. Gu, B. Zbarsky, C. McCormack, T. Langel.
[ASCII]: International Standard ISO/IEC 646:1991. Information technology - ISO 7-bit coded character set for information interchange
[DOMSTRING]: Document Object Model Core: The DOMString type, World Wide Web Consortium (W3C).
[KHRROBUSTACCESS]: KHR_robust_buffer_access_behavior OpenGL ES extension, Leech, J. and Daniell, P., August, 2014.
[MULTIPLEBUFFERING]: (Non-normative) Multiple buffering. Wikipedia.
[WEBCODECS]: (Non-normative) WebCodecs API, C. Cunningham, P. Adenot, B. Aboba. W3C.
[PREDEFINEDCOLORSPACE]: HTML Living Standard - The PredefinedColorSpace enum, WHATWG.
[WEBGPU]: WebGPU Editor's Draft, WebGPU Community Group.

Acknowledgments

This specification is produced by the Khronos WebGL Working Group.

Special thanks to: Arun Ranganathan (Mozilla), Chris Marrin (Apple), Jon Leech, Kenneth Russell (Google), Kenneth Waters (Google), Mark Callow (HI), Mark Steele (Mozilla), Oliver Hunt (Apple), Tim Johansson (Opera), Vangelis Kokkevis (Google), Vladimir Vukicevic (Mozilla), Gregg Tavares (Google)

Additional thanks to: Alan Hudson (Yumetech), Benoit Jacob (Mozilla), Bill Licea Kane (AMD), Boris Zbarsky (Mozilla), Cameron McCormack (Mozilla), Cedric Vivier (Zegami), Dan Gessel (Apple), David Ligon (Qualcomm), David Sheets (Ashima Arts), Glenn Maynard, Greg Roth (Nvidia), Jacob Strom (Ericsson), Jeff Gilbert (Mozilla), Kari Pulli (Nokia), Teddie Stenvi (ST-Ericsson), Neil Trevett (Nvidia), Per Wennersten (Ericsson), Per-Erik Brodin (Ericsson), Shiki Okasaka (Google), Tom Olson (ARM), Zhengrong Yao (Ericsson), and the members of the Khronos WebGL Working Group.

WebGL Specification

Editor's Draft Wed Sep 18 17:19:10 2024 -0700

Abstract

Status of this document

Feedback

Table of contents

Introduction

Conventions

Context Creation and Drawing Buffer Presentation

Context Creation

WebGL Resources

Security

Resource Restrictions

Defense Against Denial of Service

DOM Interfaces

Types

Context creation parameters

WebGLObject

WebGLBuffer

WebGLProgram

WebGLRenderbuffer

WebGLShader

WebGLTexture

WebGLUniformLocation

WebGLActiveInfo

Attributes

WebGLShaderPrecisionFormat

Attributes

ArrayBuffer and Typed Arrays

Attributes

Getting information about the context

Setting and getting state

Viewing and clipping

Buffer objects

Framebuffer objects

Renderbuffer objects

Texture objects

Programs and Shaders

Uniforms and attributes

Detecting context lost events

Detecting and enabling extensions

Attributes

No Client Side Arrays

No Default Textures

No Shader Binaries

Out-of-bounds fetches from the index buffer

Fixed point support

Texture Type in TexSubImage2D Calls

Feedback Loops Between Textures and the Framebuffer

GLSL ES Global Variable Initialization

Completeness of Cube Map Framebuffer Attachments

Transferring vertices when current program is null

Fragment shader output

Initial values for GLSL local and global variables

Vertex attribute conversions from normalized signed integers to floating point

Uniform and attribute name collisions

Wide point primitive clipping

References

Acknowledgments