Basic Shapes — SVG 2

Mathematically, these shape elements are equivalent to a ‘path’ element that would construct the same shape. The basic shapes may be stroked, filled and used as clip paths. All of the properties available for ‘path’ elements also apply to the basic shapes.

The equivalent path and algorithm to compute the stroke for each shape are defined in the shape sections below.

10.2. The ‘rect’ element

The ‘rect’ element defines a rectangle which is axis-aligned with the current user coordinate system. Rounded rectangles can be achieved by setting non-zero values for the rx and ry geometric properties.

The x and y coordinates refer to the left and top edges of the rectangle, in the current user coordinate system.

The width and height properties define the overall width and height of the rectangle. A negative value for either property is invalid and must be ignored. A computed value of zero for either dimension disables rendering of the element.

For rounded rectangles, the computed values of the rx and ry properties define the x- and y-axis radii of elliptical arcs used to round off the corners of the rectangle. The arc are always symmetrical along both horizontal and vertical axis; to create a rectangle with uneven corner rounding, define the shape explicitly with a ‘path’. A negative value for either property is invalid and must be ignored. A computed value of zero for either dimension, or a computed value of auto for both dimensions, results in a rectangle without corner rounding.

The used values for the x- and y-axis rounded corner radii may be determined implicitly from the other dimension (using the auto value), and are also subject to clamping so that the lengths of the straight segments of the rectangle are never negative. The used values for rx and ry are determined from the computed values by following these steps in order:

Mathematically, a ‘rect’ element is mapped to an equivalent ‘path’ element as follows, after generating absolute used values x, y, width, height, rx, and rx in user units for the user coordinate system, for each of the equivalent geometric properties following the rules specified above and in Units:

Example rect01 shows a rectangle with sharp corners. The ‘rect’ element is filled with yellow and stroked with navy.

Example rect02 shows two rounded rectangles. The rx specifies how to round the corners of the rectangles. Note that since no value has been specified for the ry attribute, the used value will be derived from the rx attribute.

10.3. The ‘circle’ element

The r attribute defines the radius of the circle. A negative value is invalid and must be ignored. A computed value of zero disables rendering of the element.

Mathematically, a ‘circle’ element is mapped to an equivalent ‘path’ element that consists of four elliptical arc segments, each covering a quarter of the circle. The path begins at the "3 o'clock" point on the radius and proceeds in a clock-wise direction (before any transformations). The rx and ry parameters to the arc commands are both equal to the used value of the r property, after conversion to local user units, while the x-axis-rotation, the large-arc-flag, and the sweep-flag are all set to zero. The coordinates are computed as follows, where cx, cy, and r are the used values of the equivalent properties, converted to user units:

Example circle01 consists of a ‘circle’ element that is filled with red and stroked with blue.

10.4. The ‘ellipse’ element

The ‘ellipse’ element defines an ellipse which is axis-aligned with the current user coordinate system based on a center point and two radii.

The rx and ry properties define the x- and y-axis radii of the ellipse. A negative value for either property is invalid and must be ignored. A computed value of zero for either dimension, or a computed value of auto for both dimensions, disables rendering of the element.

An auto value for either rx or ry is converted to a used value, following the rules given above for rectangles (but without any clamping based on width or height). Effectively, an auto value creates a circular shape whose radius is defined by a value expressed solely in one dimension; this allows for creating a circle with a radius defined in terms of one of the following:

New in SVG 2. The auto value for rx and ry was added to allow consistent parsing of these properties for both ellipses and rectangles. Previously, if either rx or ry was unspecified, the ellipse would not render.

Mathematically, an ‘ellipse’ element is mapped to an equivalent ‘path’ element that consists of four elliptical arc segments, each covering a quarter of the ellipse. The path begins at the "3 o'clock" point on the radius and proceeds in a clock-wise direction (before any transformation). The rx and ry parameters to the arc commands are the used values of the equivalent properties after conversion to local user units, while the x-axis-rotation, the large-arc-flag, and the sweep-flag are all set to zero. The coordinates are computed as follows, where cx, cy, rx, and ry are the used values of the equivalent properties, converted to user units:

Example ellipse01 below specifies the coordinates of the two ellipses in the user coordinate system established by the ‘viewBox’ attribute on the ‘svg’ element and the transform property on the ‘g’ and ‘ellipse’ elements. Both ellipses use the default values of zero for the cx and cy attributes (the center of the ellipse). The second ellipse is rotated.

10.5. The ‘line’ element

The ‘line’ element defines a line segment that starts at one point and ends at another.

Name	Value	Initial value	Animatable
x1, y1	<length-percentage> \| <number>	0	yes

Name	Value	Initial value	Animatable
x2, y2	<length-percentage> \| <number>	0	yes

A future specification may convert the ‘x1’, ‘y1’, ‘x2’, and ‘y2’ attributes to geometric properties. Currently, they can only be specified via element attributes, and not CSS.

Mathematically, a ‘line’ element can be mapped to an equivalent ‘path’ element as follows, after converting coordinates into user coordinate system user units according to Units to generate values x1, y1, x2, and y2:

Because ‘line’ elements are single lines and thus are geometrically one-dimensional, they have no interior; thus, ‘line’ elements are never filled (see the fill property).

Example line01 below specifies the coordinates of the five lines in the user coordinate system established by the ‘viewBox’ attribute on the ‘svg’ element. The lines have different thicknesses.

10.6. The ‘polyline’ element

The ‘polyline’ element defines a set of connected straight line segments. Typically, ‘polyline’ elements define open shapes.

Name	Value	Initial value	Animatable
points	<points>	(none)	yes

A future specification may convert the ‘points’ attribute to a geometric property. Currently, it can only be specified via an element attribute, and not CSS.

Mathematically, a ‘polyline’ element can be mapped to an equivalent ‘path’ element as follows:

Example polyline01 below specifies a polyline in the user coordinate system established by the ‘viewBox’ attribute on the ‘svg’ element.

10.7. The ‘polygon’ element

The ‘polygon’ element defines a closed shape consisting of a set of connected straight line segments.

Name	Value	Initial value	Animatable
points	<points>	(none)	yes

A future specification may convert the ‘points’ attribute to a geometric property. Currently, it can only be specified via an element attribute, and not CSS.

Mathematically, a ‘polygon’ element can be mapped to an equivalent ‘path’ element as follows:

Example polygon01 below specifies two polygons (a star and a hexagon) in the user coordinate system established by the ‘viewBox’ attribute on the ‘svg’ element.

10.8. DOM interfaces

10.8.1. Interface SVGRectElement

An SVGRectElement object represents a ‘rect’ element in the DOM.

[Exposed=Window]
interface SVGRectElement : SVGGeometryElement {
  [SameObject] readonly attribute SVGAnimatedLength x;
  [SameObject] readonly attribute SVGAnimatedLength y;
  [SameObject] readonly attribute SVGAnimatedLength width;
  [SameObject] readonly attribute SVGAnimatedLength height;
  [SameObject] readonly attribute SVGAnimatedLength rx;
  [SameObject] readonly attribute SVGAnimatedLength ry;
};

The x, y, width, height, rx and ry IDL attributes reflect the computed values of the x, y, width, height, rx and ry properties and their corresponding presentation attributes, respectively.

10.8.2. Interface SVGCircleElement

An SVGCircleElement object represents a ‘circle’ element in the DOM.

[Exposed=Window]
interface SVGCircleElement : SVGGeometryElement {
  [SameObject] readonly attribute SVGAnimatedLength cx;
  [SameObject] readonly attribute SVGAnimatedLength cy;
  [SameObject] readonly attribute SVGAnimatedLength r;
};

The cx, cy and r IDL attributes reflect the computed values of the cx, cy and y properties and their corresponding presentation attributes, respectively.

10.8.3. Interface SVGEllipseElement

An SVGEllipseElement object represents a ‘ellipse’ element in the DOM.

[Exposed=Window]
interface SVGEllipseElement : SVGGeometryElement {
  [SameObject] readonly attribute SVGAnimatedLength cx;
  [SameObject] readonly attribute SVGAnimatedLength cy;
  [SameObject] readonly attribute SVGAnimatedLength rx;
  [SameObject] readonly attribute SVGAnimatedLength ry;
};

The cx, cy, rx and ry IDL attributes reflect the computed values of the cx, cy, rx and ry properties and their corresponding presentation attributes, respectively.

10.8.4. Interface SVGLineElement

The SVGLineElement interface corresponds to the ‘line’ element.

[Exposed=Window]
interface SVGLineElement : SVGGeometryElement {
  [SameObject] readonly attribute SVGAnimatedLength x1;
  [SameObject] readonly attribute SVGAnimatedLength y1;
  [SameObject] readonly attribute SVGAnimatedLength x2;
  [SameObject] readonly attribute SVGAnimatedLength y2;
};

The x1, y1, x2 and y2 IDL attributes reflect the ‘x1’, ‘y1’, ‘x2’ and ‘y2’ content attributes, respectively

10.8.5. Mixin SVGAnimatedPoints

The SVGAnimatedPoints interface is used to reflect a ‘points’ attribute on a ‘polygon’ or ‘polyline’ element. It is mixed in to the SVGPolygonElement and SVGPolylineElement interfaces.

Note: In SVG 1.1 SE, the animatedPoints attribute represented the current animated value. In this version of SVG, it is simply an alias for points.

interface mixin SVGAnimatedPoints {
  [SameObject] readonly attribute SVGPointList points;
  [SameObject] readonly attribute SVGPointList animatedPoints;
};

The points and animatedPoints IDL attributes represent the current non-animated value of the reflected attribute. On getting points or animatedPoints, an SVGPointList object is returned that reflects the base value of the reflected attribute.

10.8.6. Interface SVGPointList

The SVGPointList interface is a list interface whose elements are DOMPoint objects. An SVGPointList object represents a list of points.

[Exposed=Window]
interface SVGPointList {

  readonly attribute unsigned long length;
  readonly attribute unsigned long numberOfItems;

  undefined clear();
  DOMPoint initialize(DOMPoint newItem);
  getter DOMPoint getItem(unsigned long index);
  DOMPoint insertItemBefore(DOMPoint newItem, unsigned long index);
  DOMPoint replaceItem(DOMPoint newItem, unsigned long index);
  DOMPoint removeItem(unsigned long index);
  DOMPoint appendItem(DOMPoint newItem);
  setter undefined (unsigned long index, DOMPoint newItem);
};

The behavior of all of the interface members of SVGPointList are defined in List interfaces.

This specification imposes additional requirements on the behaviour of DOMPoint objects beyond those described in the Geometry Interfaces specification, so that they can be used to reflect ‘points’ attributes.

Every DOMPoint object operates in one of three modes. It can:

reflect an element of the base value of a reflected animatable attribute (being exposed through the methods on the points member of an SVGAnimatedPoints),
represent the current translation of a given ‘svg’ element (being exposed through the currentTranslate member on SVGSVGElement), or
be detached, which is the case for DOMPoint objects created using their constructor or with createSVGPoint.

A DOMPoint object can be associated with a particular element. The associated element is used to determine which element's content attribute to update if the object reflects an attribute. Unless otherwise described, a DOMPoint object is not associated with any element.

A DOMPoint object can be designated as read only, which means that attempts to modify the object will result in an exception being thrown. When assigning to a read only DOMPoint's x, y, w or z IDL attribute, a NoModificationAllowedError must be thrown instead of updating the internal coordinate value.

Note that this applies only to the read-write DOMPoint interface; the DOMPointReadOnly interface, which is not used for reflecting the ‘points’ attribute, will already throw an exception if an attempt is made to modify it.

When assigning to a writable DOMPoint's x, y, w or z IDL attribute, the following steps are run after updating the internal coordinate value:

If the DOMPoint reflects an element of the base value of a reflected attribute, then reserialize the reflected attribute using the SVGPointList that reflects the attribute's base value.
Otherwise, if the DOMPoint represents the current translation of an ‘svg’ element and that element is the outermost svg element, then:
1. Let [a b c d e f] be the 2x3 matrix that represents the document's magnification and panning transform.
2. Let x and y be the x and y coordinates of the DOMPoint object, respectively.
3. Set the document's magnification and panning transform to [a 0 0 d x y].

10.8.7. Interface SVGPolylineElement

An SVGPolylineElement object represents a ‘polyline’ element in the DOM.

[Exposed=Window]
interface SVGPolylineElement : SVGGeometryElement {
};

SVGPolylineElement includes SVGAnimatedPoints;

10.8.8. Interface SVGPolygonElement

An SVGPolygonElement object represents a ‘polygon’ element in the DOM.

[Exposed=Window]
interface SVGPolygonElement : SVGGeometryElement {
};

SVGPolygonElement includes SVGAnimatedPoints;

Chapter 10: Basic Shapes

10.1. Introduction and definitions