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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang=en>
<head>
<title>CSS 3D Transforms</title>
<link href="../default.css" rel=stylesheet type="text/css">
<style type="text/css">
.rhs { white-space: pre-wrap; }
code { font-size: inherit; }
#box-shadow-samples td { background: white; color: black; }
</style>
<link href="http://www.w3.org/StyleSheets/TR/W3C-ED.css" rel=stylesheet
type="text/css">
<body>
<div class=head> <!--begin-logo-->
<p><a href="http://www.w3.org/"><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a> <!--end-logo-->
<h1>CSS 3D Transforms</h1>
<h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 28 January
2012</h2>
<dl>
<dt>This version:
<dd> <a
href="http://www.w3.org/TR/2012/ED-css3-3d-transforms-20120128/">http://dev.w3.org/csswg/css3-3d-transforms/</a>
<!--http://www.w3.org/TR/2012/WD-css3-3d-transforms-20120128-->
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-3d-transforms/">http://www.w3.org/TR/css3-3d-transforms/</a>
<dt>Previous version:
<dd><a href="http://www.w3.org/TR/2009/WD-css3-3d-transforms-20090320/">
http://www.w3.org/TR/2009/WD-css3-3d-transforms-20090320/</a>
<dt id=editors-list>Editors:
<dd><a href="mailto:dino@apple.com">Dean Jackson</a> (<a
href="http://www.apple.com/">Apple Inc</a>)
<dd><a href="mailto:hyatt@apple.com">David Hyatt</a> (<a
href="http://www.apple.com/">Apple Inc</a>)
<dd><a href="mailto:cmarrin@apple.com">Chris Marrin</a> (<a
href="http://www.apple.com/">Apple Inc</a>)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2012 <a
href="http://www.w3.org/"><acronym
title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a
href="http://www.csail.mit.edu/"><acronym
title="Massachusetts Institute of Technology">MIT</acronym></a>, <a
href="http://www.ercim.eu/"><acronym
title="European Research Consortium for Informatics and Mathematics">ERCIM</acronym></a>,
<a href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
<a
href="http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a>
and <a
href="http://www.w3.org/Consortium/Legal/copyright-documents">document
use</a> rules apply.</p>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>CSS 3D Transforms extends CSS Transforms to allow elements rendered by
CSS to be transformed in three-dimensional space.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<p class=note> This will be the last published Working Draft of this
specification. Work will continue with a combined CSS and SVG Transforms
specification operating under the FX Taskforce. The latest <a
href="http://dev.w3.org/csswg/css3-transforms/"> Editors' Draft</a> of the
new specification is available.</p>
<!--begin-status-->
<p>This is a public copy of the editors' draft. It is provided for
discussion only and may change at any moment. Its publication here does
not imply endorsement of its contents by W3C. Don't cite this document
other than as work in progress.
<p>The (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="mailto:www-style@w3.org?Subject=%5Bcss3-3d-transforms%5D%20PUT%20SUBJECT%20HERE">
www-style@w3.org</a> (see <a
href="http://www.w3.org/Mail/Request">instructions</a>) is preferred for
discussion of this specification. When sending e-mail, please put the text
“css3-3d-transforms” in the subject, preferably like this:
“[<!---->css3-3d-transforms<!---->] <em>…summary of
comment…</em>”
<p>This document was produced by the <a href="/Style/CSS/members">CSS
Working Group</a> (part of the <a href="/Style/">Style Activity</a>).
<p>This document was produced by a group operating under the <a
href="/Consortium/Patent-Policy-20040205/">5 February 2004 W3C Patent
Policy</a>. W3C maintains a <a href="/2004/01/pp-impl/32061/status"
rel=disclosure>public list of any patent disclosures</a> made in
connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual
knowledge of a patent which the individual believes contains <a
href="/Consortium/Patent-Policy-20040205/#def-essential">Essential
Claim(s)</a> must disclose the information in accordance with <a
href="/Consortium/Patent-Policy-20040205/#sec-Disclosure">section 6 of the
W3C Patent Policy</a>.</p>
<!--end-status-->
<p> The <a href=ChangeLog>list of changes made to this specification</a>
are available.
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#introduction"><span class=secno>1. </span>Introduction</a>
<li><a href="#transform-property"><span class=secno>2. </span> The <span
class=prop-name>‘<code
class=property>transform</code>’</span> Property </a>
<li><a href="#transform-origin-property"><span class=secno>3. </span> The
<span class=prop-name>‘<code
class=property>transform-origin</code>’</span> Property </a>
<li><a href="#transform-style-property"><span class=secno>4. </span> The
<span class=prop-name>‘<code
class=property>transform-style</code>’</span> Property </a>
<li><a href="#perspective-property"><span class=secno>5. </span> The <span
class=prop-name>‘<code
class=property>perspective</code>’</span> Property </a>
<li><a href="#perspective-origin-property"><span class=secno>6. </span>
The <span class=prop-name>‘<code
class=property>perspective-origin</code>’</span> Property </a>
<li><a href="#backface-visibility-property"><span class=secno>7. </span>
The <span class=prop-name>‘<code
class=property>backface-visibility</code>’</span> Property </a>
<li><a href="#transform-functions"><span class=secno>8. </span> The
Transformation Functions </a>
<li><a href="#animation"><span class=secno>9. </span> Transitions and
animations between transform values </a>
<li><a href="#rendering-3d"><span class=secno>10. </span> Rendering in 3d
</a>
<li><a href="#dom-interfaces"><span class=secno>11. </span> DOM Interfaces
</a>
<ul class=toc>
<li><a href="#cssmatrix-interface"><span class=secno>11.1. </span>
Extensions to CSSMatrix </a>
<li><a href="#csstransformvalue-interface"><span class=secno>11.2.
</span> CSSTransformValue </a>
</ul>
<li><a href="#references"><span class=secno>12. </span>References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#other-references">Other references</a>
</ul>
<li class=no-num><a href="#property-index">Property index</a>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<h2 id=introduction><span class=secno>1. </span>Introduction</h2>
<p><em>This section is not normative.</em>
<p> This is an enhancement to the CSS Transforms specification which
provides transforms in three dimensions. It should be read in conjunction
with that specification.
<p> This coordinate space can be modified with the <span
class=prop-name>‘<a href="#effects"><code
class=property>transform</code></a>’</span> property. Using
transform, elements can be translated, rotated and scaled in two or three
dimensional space. A perspective transform can also be applied to give a
sense of depth to the way elements are displayed. In three dimensions, a Z
axis is added, with positive z values conceptually rising perpendicularly
out of the window toward the user and negative z values falling into the
window away from the user.
<p> Any value other than ‘<code class=property>none</code>’ 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. The position on the Z axis of a transformed element does not
affect the order within a stacking context. With elements at the same
z-index, objects are drawn in order of increasing z position.
<p> Note that while <span class=prop-name>‘<a href="#effects"><code
class=property>transform</code></a>’</span> uses a three-dimensional
coordinate system, the elements themselves are not three-dimensional
objects. Instead, they exist on a two-dimensional plane (a flat surface)
and have no depth.
<h2 id=transform-property><span class=secno>2. </span> The <span
class=prop-name>‘<a href="#effects"><code
class=property>transform</code></a>’</span> Property</h2>
<p> A 2D or 3D transformation is applied to an element through the <span
class=prop-name>‘<a href="#effects"><code
class=property>transform</code></a>’</span> property. This property
contains a list of <a href="#transform-functions">transform functions</a>.
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. There are additional
functions to support 3D transformations.
<table class=propdef>
<tbody>
<tr>
<td> <em>Name:</em>
<td> <dfn id=effects>transform</dfn>
<tr>
<td> <em>Value:</em>
<td> none | <transform-function> [ <transform-function> ]*
<tr>
<td> <em>Initial:</em>
<td> none
<tr>
<td> <em>Applies to:</em>
<td> block-level and inline-level elements
<tr>
<td> <em>Inherited:</em>
<td> no
<tr>
<td> <em>Percentages:</em>
<td> refer to the size of the element's box
<tr>
<td> <em>Media:</em>
<td> visual
<tr>
<td> <em>Computed value:</em>
<td> Same as specified value.
</table>
<!-- ======================================================================================================= -->
<h2 id=transform-origin-property><span class=secno>3. </span> The <span
class=prop-name>‘<a href="#transform-origin"><code
class=property>transform-origin</code></a>’</span> Property</h2>
<p> The <span class=prop-name>‘<a href="#transform-origin"><code
class=property>transform-origin</code></a>’</span> 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 (0,0,0) in the local coordinate system, then applies the
element's transform, then moves the element back to its original position.
Note that percentage values are not allowed in the z value.
<table class=propdef>
<tbody>
<tr>
<td> <em>Name:</em>
<td> <dfn id=transform-origin>transform-origin</dfn>
<tr>
<td> <em>Value:</em>
<td> [ [ [ <percentage> | <length> | left | center | right ]
[ <percentage> | <length> | top | center | bottom ]? ]
<length> ] | [ [ [ left | center | right ] || [ top | center |
bottom ] ] <length> ]
<tr>
<td> <em>Initial:</em>
<td> 50% 50% 0
<tr>
<td> <em>Applies to:</em>
<td> block-level and inline-level elements
<tr>
<td> <em>Inherited:</em>
<td> no
<tr>
<td> <em>Percentages:</em>
<td> refer to the size of the element's box
<tr>
<td> <em>Media:</em>
<td> visual
<tr>
<td> <em>Computed value:</em>
<td> For <length> the absolute value, otherwise a percentage
</table>
<!-- ======================================================================================================= -->
<h2 id=transform-style-property><span class=secno>4. </span> The <span
class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span> Property</h2>
<p> The <span class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span> property defines
how nested elements are rendered in 3D space. If the <span
class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span> is <span
class=prop-value>‘<code class=property>flat</code>’</span>,
all children of this element are rendered flattened into the 2D plane of
the element. Therefore, rotating the element about the X or Y axes will
cause children positioned at positive or negative Z positions to appear on
the element's plane, rather than in front of or behind it. If the <span
class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span> is <span
class=prop-value>‘<code class=css>preserve-3d</code>’</span>,
this flattening is not performed, so children maintain their position in
3D space.
<p> This flattening takes place at each element, so preserving a hierarchy
of elements in 3D space requires that each ancestor in the hierarchy have
the value <span class=prop-value>‘<code
class=css>preserve-3d</code>’</span> for <span
class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span>. But since <span
class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span> affects only an
element's children, the leaf nodes in a hierarchy do not require the
perspective style.
<table class=propdef>
<tbody>
<tr>
<td> <em>Name:</em>
<td> <dfn id=transform-style>transform-style</dfn>
<tr>
<td> <em>Value:</em>
<td> flat | preserve-3d
<tr>
<td> <em>Initial:</em>
<td> flat
<tr>
<td> <em>Applies to:</em>
<td> block-level and inline-level elements
<tr>
<td> <em>Inherited:</em>
<td> no
<tr>
<td> <em>Percentages:</em>
<td> N/A
<tr>
<td> <em>Media:</em>
<td> visual
<tr>
<td> <em>Computed value:</em>
<td> Same as specified value.
</table>
<p> For some effects, the author will have to ensure that an ancestor
element to a subtree using <span class=prop-value>‘<code
class=css>preserve-3d</code>’</span> has a <span
class=prop-name>‘<a href="#transform-style"><code
class=property>transform-style</code></a>’</span> of <span
class=prop-value>‘<code class=property>flat</code>’</span> (or
the default). Otherwise, the elements in the 3D tree may be located behind
ancestor elements and, thus, invisible (hidden behind an ancestor's
background).
<p> Note that while ‘<code class=css>preserve-3d</code>’ can be
specified on an element, the effect may not be possible. Elements that
have <span class=prop-name>‘<code
class=property>overflow</code>’</span> set to <span
class=prop-value>‘<code class=property>hidden</code>’</span>
are unable to keep their children in 3D. In this case the element will
behave as if the property was set to <span class=prop-value>‘<code
class=property>flat</code>’</span>.
<div class=issue> Does transform-style: preserve-3d need to establish a
stacking context and containing block like transform does?</div>
<!-- ======================================================================================================= -->
<h2 id=perspective-property><span class=secno>5. </span> The <span
class=prop-name>‘<a href="#perspective"><code
class=property>perspective</code></a>’</span> Property</h2>
<p> The <span class=prop-name>‘<a href="#perspective"><code
class=property>perspective</code></a>’</span> property applies the
same transform as the <span
class=prop-value>perspective(<length>)</span> transform function,
except that it applies only to the positioned or transformed children of
the element, not to the transform on the element itself.
<p> If the value is <span class=prop-value>‘<code
class=property>none</code>’</span>, less than or equal to 0 no
perspective transform is applied.
<p> The use of this property with any value other than ‘<code
class=property>none</code>’ establishes a stacking context. It also
establishes a containing block (somewhat similar to position:relative),
just like the ‘<a href="#effects"><code
class=property>transform</code></a>’ property does.
<table class=propdef>
<tbody>
<tr>
<td> <em>Name:</em>
<td> <dfn id=perspective>perspective</dfn>
<tr>
<td> <em>Value:</em>
<td> none | <length>
<tr>
<td> <em>Initial:</em>
<td> none
<tr>
<td> <em>Applies to:</em>
<td> block-level and inline-level elements
<tr>
<td> <em>Inherited:</em>
<td> no
<tr>
<td> <em>Percentages:</em>
<td> N/A
<tr>
<td> <em>Media:</em>
<td> visual
<tr>
<td> <em>Computed value:</em>
<td> Same as specified value.
</table>
<!-- ======================================================================================================= -->
<h2 id=perspective-origin-property><span class=secno>6. </span> The <span
class=prop-name>‘<a href="#perspective-origin"><code
class=property>perspective-origin</code></a>’</span> Property</h2>
<p> The <span class=prop-name>‘<a href="#perspective-origin"><code
class=property>perspective-origin</code></a>’</span> property
establishes the origin for the <a
href="#perspective"><em>perspective</em></a> property. It effectively sets
the X and Y position at which the viewer appears to be looking at the
children of the element.
<table class=propdef>
<tbody>
<tr>
<td> <em>Name:</em>
<td> <dfn id=perspective-origin>perspective-origin</dfn>
<tr>
<td> <em>Value:</em>
<td> [ [ <percentage> | <length> | left | center | right ] [
<percentage> | <length> | top | center | bottom ]? ] | [ [
left | center | right ] || [ top | center | bottom ] ]
<tr>
<td> <em>Initial:</em>
<td> 50% 50%
<tr>
<td> <em>Applies to:</em>
<td> block-level and inline-level elements
<tr>
<td> <em>Inherited:</em>
<td> no
<tr>
<td> <em>Percentages:</em>
<td> refer to the size of the elemen's box
<tr>
<td> <em>Media:</em>
<td> visual
<tr>
<td> <em>Computed value:</em>
<td> Same as specified value.
</table>
<!-- ======================================================================================================= -->
<h2 id=backface-visibility-property><span class=secno>7. </span> The <span
class=prop-name>‘<a href="#backface-visibility"><code
class=property>backface-visibility</code></a>’</span> Property</h2>
<p> The <span class=prop-name>‘<a href="#backface-visibility"><code
class=property>backface-visibility</code></a>’</span> property
determines whether or not the "back" side of a transformed element is
visible when facing the viewer. With an identity transform, the front side
of an element faces the viewer. Applying a rotation about Y of 180 degrees
(for instance) would cause the back side of the element to face the
viewer.
<p> This property is useful when you place two elements back-to-back, as
you would to create a playing card. Without this property, the front and
back elements could switch places at times during an animation to flip the
card. Another example is creating a box out of 6 elements, but where you
want to see the inside faces of the box. This is useful when creating the
backdrop for a 3 dimensional stage.
<table class=propdef>
<tbody>
<tr>
<td> <em>Name:</em>
<td> <dfn id=backface-visibility>backface-visibility</dfn>
<tr>
<td> <em>Value:</em>
<td> visible | hidden
<tr>
<td> <em>Initial:</em>
<td> visible
<tr>
<td> <em>Applies to:</em>
<td> block-level and inline-level elements
<tr>
<td> <em>Inherited:</em>
<td> no
<tr>
<td> <em>Percentages:</em>
<td> N/A
<tr>
<td> <em>Media:</em>
<td> visual
<tr>
<td> <em>Computed value:</em>
<td> Same as specified value.
</table>
<!-- ======================================================================================================= -->
<h2 id=transform-functions><span class=secno>8. </span> The Transformation
Functions</h2>
<p> The value of the <a class=prop-name href="#effects">transform</a>
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 <a
href="http://www.w3.org/TR/css3-values/">CSS Values and Units.</a>
<dl>
<dt> <span class=prop-value>matrix(<number>, <number>,
<number>, <number>, <number>, <number>)</span>
<dd> specifies a 2D transformation in the form of a <a
href="http://www.w3.org/TR/SVG/coords.html#TransformMatrixDefined">transformation
matrix</a> of six values. <span
class=prop-value>matrix(a,b,c,d,e,f)</span> is equivalent to matrix3d(a,
b, 0, 0, c, d, 0, 0, 0, 0, 1, 0, e, f, 0, 1).
<dt> <span class=prop-value>matrix3d(<number>, <number>,
<number>, <number>, <number>, <number>,
<number>, <number>, <number>, <number>,
<number>, <number>, <number>, <number>,
<number>, <number>)</span>
<dd> specifies a 3D transformation as a 4x4 homogeneous matrix of 16
values in column-major order.
<dt> <span class=prop-value>translate(<translation-value>[,
<translation-value>])</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#TranslationDefined">2D
translation</a> by the vector [tx, ty], where tx is the first
translation-value parameter and ty is the optional second
translation-value parameter. If <em><ty></em> is not provided, ty
has zero as a value.
<dt> <span class=prop-value>translate3d(<translation-value>,
<translation-value>, <translation-value>)</span>
<dd> specifies a 3D translation by the vector [tx,ty,tz], with tx, ty and
tz being the first, second and third translation-value parameters
respectively. Note that <percentage> values are not allowed in the
tz translation-value, and if present will cause the propery value to be
invalid.
<dt> <span class=prop-value>translateX(<translation-value>)</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#TranslationDefined">translation</a>
by the given amount in the X direction.
<dt> <span class=prop-value>translateY(<translation-value>)</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#TranslationDefined">translation</a>
by the given amount in the Y direction.
<dt> <span class=prop-value>translateZ(<translation-value>)</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#TranslationDefined">translation</a>
by the given amount in the Z direction. Note that <percentage>
values are not allowed in the translateZ translation-value, and if
present will cause the propery value to be invalid.
<dt> <span class=prop-value>scale(<number>[, <number>])</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#ScalingDefined">2D scale</a>
operation by the [sx,sy] scaling vector described by the 2 parameters. If
the second parameter is not provided, it is takes a value equal to the
first.
<dt> <span class=prop-value>scale3d(<number>, <number>,
<number>)</span>
<dd> specifies a 3D scale operation by the [sx,sy,sz] scaling vector
described by the 3 parameters.
<dt> <span class=prop-value>scaleX(<number>)</span>
<dd> specifies a scale operation using the [sx,1,1] scaling vector, where
sx is given as the parameter.
<dt> <span class=prop-value>scaleY(<number>)</span>
<dd> specifies a scale operation using the [1,sy,1] scaling vector, where
sy is given as the parameter.
<dt> <span class=prop-value>scaleZ(<number>)</span>
<dd> specifies a scale operation using the [1,1,sz] scaling vector, where
sz is given as the parameter.
<dt> <span class=prop-value>rotate(<angle>)</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#RotationDefined">2D
rotation</a> by the angle specified in the parameter about the origin of
the element, as defined by the <a
href="#transform-origin"><em>transform-origin</em></a> property.
<dt> <span class=prop-value>rotate3d(<number>, <number>,
<number>, <angle>)</span>
<dd> specifies a clockwise 3D rotation by the angle specified in last
parameter about the [x,y,z] direction vector described by the first 3
parameters. If the direction vector is not of unit length, it will be
normalized. A direction vector that cannot be normalized, such as [0, 0,
0], will cause the rotation to not be applied. This function is
equivalent to <code>matrix3d(1 + (1-cos(angle))*(x*x-1),
-z*sin(angle)+(1-cos(angle))*x*y, y*sin(angle)+(1-cos(angle))*x*z, 0,
z*sin(angle)+(1-cos(angle))*x*y, 1 + (1-cos(angle))*(y*y-1),
-x*sin(angle)+(1-cos(angle))*y*z, 0, -y*sin(angle)+(1-cos(angle))*x*z,
x*sin(angle)+(1-cos(angle))*y*z, 1 + (1-cos(angle))*(z*z-1), 0, 0, 0, 0,
1)</code>.
<dt> <span class=prop-value>rotateX(<angle>)</span>
<dd> specifies a clockwise rotation by the given angle about the X axis.
<dt> <span class=prop-value>rotateY(<angle>)</span>
<dd> specifies a clockwise rotation by the given angle about the Y axis.
<dt> <span class=prop-value>rotateZ(<angle>)</span>
<dd> specifies a clockwise rotation by the given angle about the Z axis.
<dt> <span class=prop-value>skewX(<angle>)</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#SkewXDefined">skew
transformation along the X axis</a> by the given angle.
<dt> <span class=prop-value>skewY(<angle>)</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#SkewYDefined">skew
transformation along the Y axis</a> by the given angle.
<dt> <span class=prop-value>skew(<angle> [, <angle>])</span>
<dd> specifies a <a
href="http://www.w3.org/TR/SVG/coords.html#SkewXDefined">skew
transformation along the X and Y axes</a>. The first angle parameter
specifies the skew on the X axis. The second angle parameter specifies
the skew on the Y axis. If the second parameter is not given then a value
of 0 is used for the Y angle (ie. no skew on the Y axis).
<dt> <span class=prop-value>perspective(<length>)</span>
<dd> specifies a perspective projection matrix. This matrix maps a
<em>viewing cube</em> onto a pyramid whose base is infinitely far away
from the viewer and whose peak represents the viewer's position. The
viewable area is the region bounded by the four edges of the viewport
(the portion of the browser window used for rendering the webpage between
the viewer's position and a point at a distance of infinity from the
viewer). The <em>depth</em>, given as the parameter to the function,
represents the distance of the z=0 plane from the viewer. Lower values
give a more flattened pyramid and therefore a more pronounced perspective
effect. For example, a value of 1000px gives a moderate amount of
foreshortening and a value of 200px gives an extreme amount. The matrix
is computed by starting with an identity matrix and replacing the value
at row 3, column 4 with the value -1/depth. The value for depth must be
greater than zero, otherwise the function is invalid.
</dl>
<!-- ======================================================================================================= -->
<h2 id=animation><span class=secno>9. </span> Transitions and animations
between transform values</h2>
<p> When animating or transitioning the value of a transform property the
rules described below are applied. The ‘<code
class=property>from</code>’ transform is the transform at the start
of the transition or current keyframe. The ‘<code
class=property>end</code>’ transform is the transform at the end of
the transition or current keyframe.
<ul>
<li> If the ‘<code class=property>from</code>’ and
‘<code class=property>to</code>’ transforms are both single
functions of the same type:
<ul>
<li> For translate, translate3d, translateX, translateY, translateZ,
scale, scale3d, scaleX, scaleY, scaleZ, rotate, rotateX, rotateY,
rotateZ, skewX and skewY functions:
<ul>
<li> the individual components of the function are interpolated
numerically.
</ul>
<li> For perspective, matrix, matrix3d and rotate3d:
<ul>
<li> the values are first converted to a 4x4 matrix, then decomposed
using <a href="http://tog.acm.org/GraphicsGems/gemsii/unmatrix.c">the
method described by unmatrix</a> into separate translation, scale,
rotation, skew and perspective matrices, then each decomposed matrix
is interpolated numerically, and finally combined in order to produce
a resulting 4x4 matrix.
</ul>
</ul>
<li> If both the ‘<code class=property>from</code>’ and
‘<code class=property>to</code>’ transforms are "none":
<ul>
<li> There is no interpolation necessary
</ul>
<li> If one of the ‘<code class=property>from</code>’ or
‘<code class=property>to</code>’ transforms is "none":
<ul>
<li> The ‘<code class=property>none</code>’ is replaced by
an equivalent identity function list for the corresponding transform
function list.
<p> For example, if the ‘<code class=property>from</code>’
transform is "scale(2)" and the ‘<code
class=property>to</code>’ transform is "none" then the value
"scale(1)" will be used as the ‘<code
class=property>to</code>’ value, and animation will proceed
using the rule above. Similarly, if the ‘<code
class=property>from</code>’ transform is "none" and the
‘<code class=property>to</code>’ transform is "scale(2)
rotate(50deg)" then the animation will execute as if the ‘<code
class=property>from</code>’ value is "scale(1) rotate(0)".</p>
<p> The identity functions are translate(0), translate3d(0, 0, 0),
translateX(0), translateY(0), translateZ(0), scale(1), scale3d(1, 1,
1), scaleX(1), scaleY(1), scaleZ(1), rotate(0), rotate3d(1, 1, 1, 0),
rotateX(0), rotateY(0), rotateZ(0), skewX(0), skewY(0), matrix(1, 0,
0, 1, 0, 0) and matrix3d(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0,
1).</p>
</ul>
<li> If both the ‘<code class=property>from</code>’ and
‘<code class=property>to</code>’ transforms have the same
number of transform functions and corresponding functions in each
transform list are of the same type:
<ul>
<li> Each transform function is animated with its corresponding
destination function in isolation using the rules described above. The
individual values are then applied as a list to produce resulting
transform value.
</ul>
<li> Otherwise:
<ul>
<li> The transform function lists are each converted into the equivalent
matrix3d value and animation proceeds using the rule for a single
function above.
</ul>
</ul>
<!-- ======================================================================================================= -->
<h2 id=rendering-3d><span class=secno>10. </span> Rendering in 3d</h2>
<p> Since CSS only describes a flat rendering model, without perspective,
and where everything faces the viewer front on, once three-dimensional
transforms are supported it is necessary to describe how an element should
be drawn in different orientations.
<p> While CSS specifies a rendering order for properties, such as
background, border and content, this rendering order does not imply any
three-dimensional structure. That is, if an element is rotated so that its
back face is facing the user, it will appear like a mirrored version of
the front face. In other words, the transforms are applied to the rendered
version of the elements, as if the element is rendered into an offscreen
buffer, and that buffer is transformed and composited onto the page.</p>
<!-- ======================================================================================================= -->
<h2 id=dom-interfaces><span class=secno>11. </span> DOM Interfaces</h2>
<p> This section describes the interfaces and functionality added to the
DOM to support runtime access to the functionality described above.</p>
<!-- ============================================================ -->
<h3 id=cssmatrix-interface><span class=secno>11.1. </span> Extensions to
CSSMatrix</h3>
<dl>
<dt> <b>Interface <i><a id=DOM-CSSMatrix
name=DOM-CSSMatrix>CSSMatrix</a></i></b>
<dd>
<p> The following extends the <code>CSSMatrix</code> interface definition
specified in the CSS3 2D Transforms Module.</p>
<dl>
<dt> <b>IDL Definition</b>
<dd>
<div class=idl-code>
<pre>
[Supplemental] interface CSSMatrix {
attribute float m11;
attribute float m12;
attribute float m13;
attribute float m14;
attribute float m21;
attribute float m22;
attribute float m23;
attribute float m24;
attribute float m31;
attribute float m32;
attribute float m33;
attribute float m34;
attribute float m41;
attribute float m42;
attribute float m43;
attribute float m44;
CSSMatrix translate(in float x, in float y, optional in float z);
CSSMatrix scale(in float scaleX, optional in float scaleY, optional in float scaleZ);
CSSMatrix rotate(in float rotX, optional in float rotY, optional in float rotZ);
CSSMatrix rotateAxisAngle(in float x, in float y, in float z, in float angle);
};</pre>
</div>
<br>
</dd>
<!-- IDL -->
<dt> <b>Attributes</b>
<dd>
<dl>
<dt> <code class=attribute-name><a id=DOM-CSSMatrix-matrix
name=DOM-CSSMatrix-matrix>m11-m44</a></code> of type
<code>float</code>
<dd> Each of these attributes represents one of the values in the 4x4
matrix. For instance m12 represents the value in the 2nd column of
the first row.<br>
</dl>
</dd>
<!-- Attributes -->
<dt> <b>Methods</b>
<dd>
<dl><!-- ===================================================== -->
<dt> <code class=method-name><a id=DOM-CSSMatrix-translate
name=DOM-CSSMatrix-translate>translate</a></code>
<dd>
<div class=method> The <code>translate</code> method returns a new
matrix which is this matrix post multiplied by a translation matrix
containing the passed values. If the z component is undefined, a 0
value is used in its place. This matrix is not modified.
<div class=parameters> <b>Parameters</b>
<div class=paramtable>
<dl>
<dt> <code class=parameter-name>x</code> of type
<code>float</code>
<dd> The X component of the translation value.<br>
<dt> <code class=parameter-name>y</code> of type
<code>float</code>
<dd> The Y component of the translation value.<br>
<dt> <code class=parameter-name>z</code> of type
<code>float</code>
<dd> The (optional) Z component of the translation value.<br>
</dl>
</div>
</div>
<!-- parameters -->
<div class=return-value> <b>Return Value</b>
<div class=returnvalue>
<dl>
<dt> <code>CSSMatrix</code>