CSS 2D Transforms allows elements rendered by CSS to be transformed in two-dimensional space.
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This is the first public Working Draft of the “css3-2d-transforms” series.
Table of contentstransform’ Property transform-origin’ Property This section is not normative.
The CSS visual formatting model describes a coordinate system within which each element is positioned. Positions and sizes in this coordinate space can be thought of as being expressed in pixels, starting in the upper left corner of the parent with positive values proceeding to the right and down.
This coordinate space can be modified with the ‘transform’ property. Using transform, elements can be translated, rotated and scaled in two dimensional space. The coordinate space behaves as described in the coordinate system transformations section of the SVG 1.1 specification. This is a coordinate system with two axes: the X axis increases horizontally to the right; the Y axis increases vertically downwards.
Specifying a value other than ‘none’ for the ‘transform’ property establishes a new local coordinate system at the element that it is applied to. Transformations are cumulative. That is, elements establish their local coordinate system within the coordinate system of their parent. In this way, a ‘transform’ property effectively accumulates all the ‘transform’ properties of its ancestors. The accumulation of these transforms defines a current transformation matrix (CTM) for the element.
The transform property does not affect the flow of the content surrounding the transformed element. However, the value of the overflow area takes into account transformed elements. This behavior is similar to what happens when elements are translated via relative positioning. Therefore, if the value of the ‘overflow’ property is ‘scroll’ or ‘auto’, scrollbars will appear as needed to see content that is transformed outside the visible area.
Any value other than ‘none’ for the transform results in the creation of both a stacking context and a containing block. The object acts as though position: relative has been specified, but also acts as a containing block for fixed positioned descendants.
Need to go into more detail here about why fixed positioned objects should do this, i.e., that it's much harder to implement otherwise.
There are two roles for transformations in layout: (1) transformations that adjust the position of the affected content without changing the normal layout of that content (much like relative positioning) and (2) transformation of the content prior to layout that affects the layout of that content. See
http://lists.w3.org/Archives/Public/www-style/2007Oct/0209for examples of both cases. The "transform" property (as defined in this document) is equally useful for both roles. This document is focused on satisfying the first role. There is, however, an architectural question that arises because there needs to be a way to distinguish which role an author of a stylesheet wants. The key question is which is the default behavior/role for the "transform" property and how is the other behavior/role indicated by a stylesheet author. One possibility is to use the position property, particularly position: relative, to trigger the first role; another possibility is to make the first role the default which leaves the question as to how to indicate the second role. If you have an opinion on this topic, please send feedback.
What do fixed backgrounds do in transforms? They should probably ignore the transform completely, since - even transformed - the object should be acting as "porthole" through which the fixed background can be viewed in its original form.
This property should also be applicable to SVG elements.
We also need to specify that SVG transforms *do* combine with this transform, e.g., if a <foreignObject> is inside transformed SVG and then defines a transform of its own. This means we may potentially have to examine the current SVG transform and combine with it to set the correct transform.
2 The ‘transform’ Property
A two-dimensional transformation is applied to an element through the ‘transform’ property. This property contains a list of transform functions. The final transformation value for an element is obtained by performing a matrix concatenation of each entry in the list. The set of transform functions is similar to those allowed by SVG.
transform-origin’ Property
The ‘transform-origin’ property establishes the origin of transformation for an element. This property is applied by first translating the element by the negated value of the property, then applying the element's transform, then translating by the property value. This effectively moves the desired transformation origin of the element to (0,0) in the local coordinate system, then applies the element's transform, then moves the element back to its original position.
The value of the transform property is a list of <transform-functions>, applied in the order provided. The individual transform functions are separated by whitespace. The following is a list of allowed transform functions. In this list the type <translation-value> is defined as a <length> or <percentage> value, and the <angle> type is defined by CSS Values and Units.
The <translation-value> values are defined as [<percentage> | <length>]. All other value types are described as CSS types. If a list of transforms is provided, then the net effect is as if each transform had been specified separately in the order provided. For example,
<div style="transform:translate(-10px,-20px) scale(2) rotate(45deg) translate(5px,10px)"/>
is functionally equivalent to:
<div style="transform:translate(-10px,-20px)">
<div style="transform:scale(2)">
<div style="transform:rotate(45deg)">
<div style="transform:translate(5px,10px)">
</div>
</div>
</div>
</div>
div {
transform: translate(100px, 100px);
}
Move the element by 100 pixels in both the X and Y directions.
div {
height: 100px; width: 100px;
transform: translate(80px, 80px) scale(1.5, 1.5) rotate(45deg);
}
Move the element by 80 pixels in both the X and Y directions, then scale the element by 150%, then rotate it 45 degrees clockwise about the Z axis. Note that the scale and rotate operate about the center of the element, since the element has the default transform-origin of 50% 50%.
6 Transitions and animations between transform valuesWhen animating or transitioning the value of a transform property the rules described below are applied. The ‘from’ transform is the transform at the start of the transition or current keyframe. The ‘end’ transform is the transform at the end of the transition or current keyframe.
from’ and ‘to’ transforms are both single functions of the same type:
from’ and ‘to’ transforms are "none":
from’ or ‘to’ transforms is "none":
none’ is replaced by an equivalent identity function list for the corresponding transform function list.
For example, if the ‘from’ transform is "scale(2)" and the ‘to’ transform is "none" then the value "scale(1)" will be used as the ‘to’ value, and animation will proceed using the rule above. Similarly, if the ‘from’ transform is "none" and the ‘to’ transform is "scale(2) rotate(50deg)" then the animation will execute as if the ‘from’ value is "scale(1) rotate(0)".
The identity functions are translate(0), translateX(0), translateY(0), scale(1), scaleX(1), scaleY(1), rotate(0), rotateX(0), rotateY(0), skewX(0), skewY(0), and matrix(1, 0, 0, 1, 0, 0).
from’ and ‘to’ transforms have the same number of transform functions and corresponding functions in each transform list are of the same type:
This section describes the interfaces and functionality added to the DOM to support runtime access to the functionality described above.
7.1 PointThe Point interface represents a point in two-dimensional space.
interface Point {
attribute float x;
attribute float y;
};
x of type float
y of type float
The following 2 functions are added to the Window interface. They provide conversions between the page and node coordinate spaces.
interface Window {
...
Point convertPointFromPageToNode(in Node node, in Point point);
Point convertPointFromNodeToPage(in Node node, in Point point);
...
};
convertPointFromPageToNode
The
convertPointFromPageToNode
method returns a point in the coordinate space of the passed Node that is at the same location in the page as the passed point, which is in the coordinate space of the page.
Parametersnode of type Node
point of type Point
Return Value
Point
No Exceptions
convertPointFromNodeToPage
The
convertPointFromNodeToPage
method returns a point in the coordinate space of the page that is at the same location in the page as the passed point, which is in the coordinate space of the passed Node.
Parametersnode of type Node
point of type Point
Return Value
Point
No Exceptions
The CSSMatrix interface represents a 4x4 homogeneous matrix.
interface CSSMatrix {
attribute float a;
attribute float b;
attribute float c;
attribute float d;
attribute float e;
attribute float f;
void setMatrixValue(in DOMString string) raises(DOMException);
CSSMatrix multiply(in CSSMatrix secondMatrix);
CSSMatrix inverse() raises(DOMException);
CSSMatrix translate(in float x, in float y);
CSSMatrix scale(in float scaleX, in float scaleY);
CSSMatrix rotate(in float angle);
};
a-f of type float
setMatrixValue
The
setMatrixValue
method replaces the existing matrix with one computed from parsing the passed string as though it had been assigned to the transform property in a CSS style rule.
Parametersstring of type DOMString
No Return Value
ExceptionsSYNTAX_ERR
multiply
The
multiply
method returns a new CSSMatrix which is the result of this matrix multiplied by the passed matrix, with the passed matrix to the right. This matrix is not modified.
ParameterssecondMatrix of type CSSMatrix
CSSMatrix
No Exceptions
inverse
The
inverse
method returns a new matrix which is the inverse of this matrix. This matrix is not modified.
No Parameters
Return ValueCSSMatrix
NOT_SUPPORTED_ERROR
translate
The
translate
method returns a new matrix which is this matrix post multiplied by a translation matrix containing the passed values. This matrix is not modified.
Parametersx of type float
y of type float
CSSMatrix
No Exceptions
scale
The
scale
method returns a new matrix which is this matrix post multiplied by a scale matrix containing the passed values. If the z component is undefined, a 1 value is used in its place. If the y component is undefined, the x component value is used in its place. This matrix is not modified.
ParametersscaleX of type float
scaleY of type float
CSSMatrix
No Exceptions
rotate
The
rotate
method returns a new matrix which is this matrix post multiplied by a rotation matrix. The rotation value is in degrees. This matrix is not modified.
Parametersangle of type float
CSSMatrix
No Exceptions
The CSSTransformValue interface represents one transform function in the transform property. The operationType defines which operation is represented. The object also contains a list of values, which are the parameters of the function, in the same order in which they appear in the transform functions.
interface CSSTransformValue : CSSValueList {
// 2D OperationTypes
const unsigned short CSS_TRANSLATE = 1;
const unsigned short CSS_TRANSLATEX = 2;
const unsigned short CSS_TRANSLATEY = 3;
const unsigned short CSS_ROTATE = 4;
const unsigned short CSS_SCALE = 5;
const unsigned short CSS_SCALEX = 6;
const unsigned short CSS_SCALEY = 7;
const unsigned short CSS_SKEW = 8;
const unsigned short CSS_SKEWX = 9;
const unsigned short CSS_SKEWY = 10;
const unsigned short CSS_MATRIX = 11;
attribute unsigned short operationType;
CSSMatrix getCSSMatrix() raises(DOMException);
};
operationType of type unsigned short
getCSSMatrix
The
getCSSMatrix
method returns a CSSMatrix object representing this transform.
No Parameters
Return ValueCSSMatrix
NOT_SUPPORTED_ERROR
In addition to the interfaces listed above, the getComputedStyle method of the Window object has been updated. The transform property of the style object returned by getComputedStyle contains a single CSSTransformValue with a type of CSS_MATRIX. The 6 parameters represent the 3x2 matrix that is the result of applying the individual functions listed in the transform property.
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