css-transitions/Overview.src.html

Wed, 23 Apr 2014 18:02:06 +0900

author
Koji Ishii <kojiishi@gluesoft.co.jp>
date
Wed, 23 Apr 2014 18:02:06 +0900
changeset 13790
0423da3ec2a8
parent 9871
de0aa877c41b
child 14185
f89d8556ad29
permissions
-rw-r--r--

[css-text] issues-lc-2013 updated up to 68

     1 <!DOCTYPE html PUBLIC '-//W3C//DTD HTML 4.01//EN'
     2   'http://www.w3.org/TR/html4/strict.dtd'>
     4 <html lang="en">
     5 <head>
     6   <title>CSS Transitions</title>
     7   <script src='http://test.csswg.org/harness/annotate.js#css-transitions-1_dev' type='text/javascript' defer></script>
     8   <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
     9   <link rel="stylesheet" type="text/css" href="../default.css">
    10   <style type="text/css">
    11     table.animatable-properties {
    12       border-collapse: collapse;
    13     }
    14     table.animatable-properties td {
    15       padding: 0.2em 1em;
    16       border: 1px solid black;
    17     }
    18     div.prod { margin: 1em 2em; }
    19   </style>
    20   <link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS].css">
    21 </head>
    23 <body>
    25 <div class="head">
    26 <!--logo-->
    28 <h1>CSS Transitions</h1>
    30 <h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>
    31 <dl>
    32   <dt>This version:
    33     <dd>
    34     <a href="[VERSION]">[VERSION]</a>
    35   <dt>Latest version:
    36     <dd><a href="http://www.w3.org/TR/css3-transitions/">
    37       [LATEST]</a>
    38   <dt>Editor's draft:
    39     <dd><a href="http://dev.w3.org/csswg/css-transitions/">http://dev.w3.org/csswg/css-transitions/</a>
    40     (<a href="https://dvcs.w3.org/hg/csswg/log/tip/css-transitions/Overview.src.html">change log</a>,
    41     <a href="https://dvcs.w3.org/hg/csswg/log/tip/css3-transitions/Overview.src.html">older change log</a>)
    42   <dt>Previous version:
    43     <dd><a href="http://www.w3.org/TR/2013/WD-css3-transitions-20131119/">http://www.w3.org/TR/2013/WD-css3-transitions-20131119/</a>
    44   <dt id="editors-list">Editors:
    45     <dd><a href="mailto:dino@apple.com">Dean Jackson</a> (<a
    46       href="http://www.apple.com/">Apple Inc</a>)
    47     <dd><a href="mailto:hyatt@apple.com">David Hyatt</a> (<a
    48       href="http://www.apple.com/">Apple Inc</a>)
    49     <dd><a href="mailto:cmarrin@apple.com">Chris Marrin</a> (<a
    50       href="http://www.apple.com/">Apple Inc</a>)
    51     <dd class=vcard><a class=fn href="http://dbaron.org/">L. David Baron</a> (<a
    52       class=org href="http://www.mozilla.org/">Mozilla</a>)
    54   <dt>Issues list:
    55     <dd>In Bugzilla:
    56         <a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&amp;product=CSS&amp;component=Transitions&amp;resolution=---&amp;status_whiteboard=defer%20to%20level%202&amp;status_whiteboard_type=notregexp">for this level</a>,
    57         <a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&amp;product=CSS&amp;component=Transitions&amp;resolution=---">for all levels</a>
    59   <dt>Feedback:
    60     <dd><a href="mailto:www-style@w3.org?subject=%5Bcss-transitions%5D%20feedback">www-style@w3.org</a>
    61         with subject line &ldquo;<kbd>[css-transitions] <var>&hellip; message topic &hellip;</var></kbd>&rdquo;
    62         (<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/">archives</a>)
    64   <dt>Test suite:
    65     <dd>  <a href="http://test.csswg.org/suites/css-transitions-1/nightly-unstable/">http://test.csswg.org/suites/css-transitions-1/nightly-unstable/</a>
    66 </dl>
    68 <!--copyright-->
    70 <hr title="Separator for header">
    71 </div>
    73 <h2 class="no-num no-toc" id="abstract">Abstract</h2>
    75 <p>CSS Transitions allows property changes in CSS values to occur smoothly
    76   over a specified duration.
    78 <h2 class="no-num no-toc" id="status">Status of this document</h2>
    79 <!--status-->
    81 <p>
    82   <strong>This document</strong> is expected to be relatively close to
    83   last call.  While some issues raised have yet to be addressed, new
    84   features are extremely unlikely to be considered for this level.
    85 </p>
    87 <h2 class="no-num no-toc" id="contents">Table of Contents</h2>
    88 <!--toc-->
    91 <h2 id="introduction">Introduction</h2>
    93       <p><em>This section is not normative.</em>
    94       <p>
    95         This document introduces new CSS features to enable <em>implicit transitions</em>, which describe how CSS properties can be made to change smoothly from one value to another over a given duration.
    96       </p>
    98 <h2 id="transitions"><a title="" id="transitions-">Transitions</a></h2>
    99       <p>
   100         Normally when the value of a CSS property changes, the rendered result is instantly updated, with the affected elements immediately changing from the old property value to the new property value. This section describes a way to specify transitions using new CSS properties. These properties are used to animate smoothly from the old state to the new state over time.
   101       </p>
   102       <p>
   103         For example, suppose that transitions of one second have been defined on the 'left' and
   104         'background-color' properties. The following diagram illustrates the effect of updating those properties on an element, in this case moving it to the right and changing the background from red to blue. This assumes other transition parameters still have their default values.
   105       </p>
   106       <div class="figure">
   107         <img src="transition1.png" alt="">
   108       </div>
   109       <p class="caption">
   110         Transitions of 'left' and 'background-color'
   111       </p>
   112       <p>
   113         Transitions are a presentational effect. The computed value of a property transitions over time from the old value to the new value. Therefore if a script queries the computed style of a property as it is transitioning, it will see an intermediate value that represents the current animated value of the property.
   114       </p>
   115       <p>
   116         Only animatable CSS properties can be transitioned. See the table at the end of this document for a list 
   117         of properties that are animatable.
   118       </p>
   119       <p>
   120         The transition for a property is defined using a number of new properties. For example:
   121       </p>
   122       <div class="example">
   123         <p style="display:none">
   124           Example(s):
   125         </p>
   126         <pre>
   127   div {
   128     transition-property: opacity;
   129     transition-duration: 2s;
   130   }
   131   </pre>The above example defines a transition on the 'opacity' property that, when a new value is assigned to it, will cause a smooth change between the old value and the new value over a period of two seconds.
   132       </div>
   133       <p>
   134         Each of the transition properties accepts a comma-separated list, allowing multiple transitions to be defined, each acting on a different property. In this case, the individual transitions take their parameters from the same index in all the lists. For example:
   135       </p>
   136       <div class="example">
   137         <p style="display:none">
   138           Example(s):
   139         </p>
   140         <pre>
   141   div {
   142     transition-property: opacity, left;
   143     transition-duration: 2s, 4s;
   144   }
   146   </pre>This will cause the 'opacity' property to transition over a period of two seconds and the left property to transition over a period of four seconds.
   147       </div>
   149       <p id="list-matching">
   150         In the case where the lists of values in transition properties
   151         do not have the same length, the length of the
   152         'transition-property' list determines the number of items in
   153         each list examined when starting transitions.  The lists are
   154         matched up from the first value: excess values at the end are
   155         not used.  If one of the other properties doesn't have enough
   156         comma-separated values to match the number of values of
   157         'transition-property', the UA must calculate its used value by
   158         repeating the list of values until there are enough.  This
   159         truncation or repetition does not affect the computed value.
   160         <span class="note">
   161           Note: This is analogous to the behavior of the 'background-*'
   162           properties, with 'background-image' analogous to
   163           'transition-property'.
   164         </span>
   165       </p>
   167       <div class="example">
   168         <p style="display:none">
   169           Example(s):
   170         </p>
   171       <pre>
   172       div {
   173         transition-property: opacity, left, top, width;
   174         transition-duration: 2s, 1s;
   175       }
   176       </pre>The above example defines a transition on the 'opacity' property of 2 seconds duration, a
   177       transition on the 'left' property of 1
   178       second duration, a transition on the 'top' property of 2 seconds duration and a
   179       transition on the 'width' property of 1
   180       second duration.
   182       </div>
   184       <p>
   185         While authors can use transitions to create dynamically changing content,
   186         dynamically changing content can lead to seizures in some users.
   187         For information on how to avoid content that can lead to seizures, see
   188         <a href="http://www.w3.org/TR/WCAG20/#seizure">Guideline 2.3:
   189         Seizures:
   190         Do not design content in a way that is known to cause seizures</a>
   191         ([[WCAG20]]).
   192       </p>
   194       <!-- ======================================================================================================= -->
   195       <h3 id="transition-property-property"><a title="" id="the-transition-property-property-">
   196         The 'transition-property' Property
   197       </a></h3>
   198       <p>
   199         The 'transition-property' property specifies the name of the CSS property to which the transition is applied.
   200       </p>
   201       <table class="propdef">
   202         <tbody>
   203           <tr>
   204             <th>
   205               Name:
   206             </th>
   207             <td>
   208               <dfn id="transition-property">transition-property</dfn>
   209             </td>
   210           </tr>
   211           <tr>
   212             <th>
   213               Value:
   214             </th>
   215             <td>
   216               none | <span>&lt;single-transition-property&gt;</span> [ ',' <span>&lt;single-transition-property&gt;</span> ]*
   217             </td>
   218           </tr>
   219           <tr>
   220             <th>
   221               Initial:
   222             </th>
   223             <td>
   224               all
   225             </td>
   226           </tr>
   227           <tr>
   228             <th>
   229               Applies to:
   230             </th>
   231             <td>
   232               all elements, :before and :after pseudo elements
   233             </td>
   234           </tr>
   235           <tr>
   236             <th>
   237               Inherited:
   238             </th>
   239             <td>
   240               no
   241             </td>
   242           </tr>
   243           <tr>
   244             <th>
   245               Animatable:
   246             </th>
   247             <td>
   248               no
   249             </td>
   250           </tr>
   251           <tr>
   252             <th>
   253               Percentages:
   254             </th>
   255             <td>
   256               N/A
   257             </td>
   258           </tr>
   259           <tr>
   260             <th>
   261               Media:
   262             </th>
   263             <td>
   264               visual
   265             </td>
   266           </tr>
   267           <tr>
   268             <th>
   269               Computed value:
   270             </th>
   271             <td>
   272               Same as specified value.
   273             </td>
   274           </tr>
   275           <tr>
   276             <th>
   277               Canonical order:
   278             </th>
   279             <td>
   280               <abbr title="follows order of property value definition">per grammar</abbr>
   281             </td>
   282           </tr>
   283         </tbody>
   284       </table>
   286       <div class="prod">
   287         <dfn id="single-transition-property">&lt;single-transition-property&gt;</dfn> = all | &lt;IDENT&gt;
   288       </div>
   290       <p>
   291         A value of ''none'' means that no property will transition.
   292         Otherwise, a list of properties to be transitioned, or the
   293         keyword ''all'' which indicates that all properties are to be
   294         transitioned, is given.
   295       </p>
   297       <p>
   298         If one of the identifiers listed is not a recognized property
   299         name or is not an animatable property, the implementation must
   300         still start transitions on the animatable properties in the
   301         list using the duration, delay, and timing function at their
   302         respective indices in the lists for 'transition-duration',
   303         'transition-delay', and 'transition-timing-function'.  In other
   304         words, unrecognized or non-animatable properties must be kept in
   305         the list to preserve the matching of indices.
   306       </p>
   308       <p>
   309         The keywords ''none'', ''inherit'', and ''initial'' are not
   310         permitted as items within a list of more that one identifier;
   311         any list that uses them is syntactically invalid.
   312         In other words, the &lt;IDENT&gt; production in
   313         <span>&lt;single-transition-property&gt;</span> matches any
   314         identifier other than these three keywords.
   315       </p>
   317       <p>
   318         For the keyword ''all'', or if one of the identifiers listed is a
   319         shorthand property, implementations must start transitions for
   320         any of its longhand sub-properties that are animatable (or, for
   321         ''all'', all animatable properties), using the duration, delay,
   322         and timing function at the index corresponding to the shorthand.
   323       </p>
   324       <p>
   325         If a property is specified multiple times in the value of
   326         'transition-property' (either on its own, via a shorthand that
   327         contains it, or via the ''all'' value), then the transition that
   328         starts uses the duration, delay, and timing function at the
   329         index corresponding to the <em>last</em> item in the value of
   330         'transition-property' that calls for animating that property.
   331       </p>
   332       <p class="note">
   333         Note:  The ''all'' value and 'all' shorthand
   334         property work in similar ways, so the
   335         ''all'' value is just like a shorthand that
   336         covers all properties.
   337       </p>
   339       <!-- ======================================================================================================= -->
   340       <h3 id="transition-duration-property"><a title="" id="the-transition-duration-property-">
   341         The 'transition-duration' Property
   342       </a></h3>
   343       <p>
   344         The 'transition-duration' property defines the length of time that a transition takes.
   345       </p>
   346       <table class="propdef">
   347         <tbody>
   348           <tr>
   349             <th>
   350               Name:
   351             </th>
   352             <td>
   353               <dfn id="transition-duration">transition-duration</dfn>
   354             </td>
   355           </tr>
   356           <tr>
   357             <th>
   358               Value:
   359             </th>
   360             <td>
   361               <span>&lt;time&gt;</span> [, <span>&lt;time&gt;</span>]*
   362             </td>
   363           </tr>
   364           <tr>
   365             <th>
   366               Initial:
   367             </th>
   368             <td>
   369               0s
   370             </td>
   371           </tr>
   372           <tr>
   373             <th>
   374               Applies to:
   375             </th>
   376             <td>
   377               all elements, :before and :after pseudo elements
   378             </td>
   379           </tr>
   380           <tr>
   381             <th>
   382               Inherited:
   383             </th>
   384             <td>
   385               no
   386             </td>
   387           </tr>
   388           <tr>
   389             <th>
   390               Animatable:
   391             </th>
   392             <td>
   393               no
   394             </td>
   395           </tr>
   396           <tr>
   397             <th>
   398               Percentages:
   399             </th>
   400             <td>
   401               N/A
   402             </td>
   403           </tr>
   404           <tr>
   405             <th>
   406               Media:
   407             </th>
   408             <td>
   409               interactive
   410             </td>
   411           </tr>
   412           <tr>
   413             <th>
   414               Computed value:
   415             </th>
   416             <td>
   417               Same as specified value.
   418             </td>
   419           </tr>
   420           <tr>
   421             <th>
   422               Canonical order:
   423             </th>
   424             <td>
   425               <abbr title="follows order of property value definition">per grammar</abbr>
   426             </td>
   427           </tr>
   428         </tbody>
   429       </table>
   430       <p>
   431         This property specifies how long the transition from the old value to the new value should take. By default the value is ''0s'', meaning that the transition is immediate (i.e. there will be no animation). A negative value for 'transition-duration' renders the declaration invalid.
   432       </p>
   434       <!-- =======================================================================================================   
   435         -->
   437       <h3 id="transition-timing-function-property"><a title="" id="transition-timing-function_tag">
   438         The 'transition-timing-function' Property
   439       </a></h3>
   440       <p>
   441         The 'transition-timing-function' property
   442         describes how the intermediate values used during a transition will be
   443         calculated. It allows for a transition to change speed over its
   444         duration. These effects are commonly called <em>easing</em> functions.
   445         In either case, a mathematical function that provides a smooth curve is
   446         used.
   447       </p>
   448       <p>
   449         Timing functions are either defined as a stepping function or 
   450         a <a
   451         href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve#Cubic_B.C3.A9zier_curves">cubic
   452         B&eacute;zier curve</a>. 
   453         The timing function takes as its input
   454         the current elapsed percentage of the transition duration
   455         and outputs the percentage of the way the transition is
   456         from its start value to its end value.
   457         How this output is used is defined by
   458         the <a href="#animatable-types">interpolation rules</a>
   459         for the value type.
   460       </p>
   461       <p>
   462         A <a href="http://en.wikipedia.org/wiki/Step_function">stepping</a>
   463         function is defined by a number that divides the domain of operation
   464         into equally sized intervals. Each subsequent interval is a equal step
   465         closer to the goal state. The function also specifies whether the
   466         change in output percentage happens at the start or end of the
   467         interval (in other words, if 0% on the input percentage is the point
   468         of initial change).
   469       </p>
   470       <div class="figure">
   471         <img src="step.png" alt="The step timing function splits
   472           the function domain into a number of disjoint straight line
   473           segments. steps(1, start) is a function whose
   474           output value is 1 for all input values. steps(1, end) is a function whose
   475           output value is 0 for all input values less than 1, and output
   476           is 1 for the input value of 1. steps(3, start) is a function that
   477           divides the input domain into three segments, each 1/3 in length,
   478           and 1/3 above the previous segment, with the first segment starting
   479           at 1/3. steps(3, end) is a function that
   480           divides the input domain into three segments, each 1/3 in length,
   481           and 1/3 above the previous segment, with the first segment starting
   482           at 0.">
   483       </div>
   484       <p class="caption">
   485         Step timing functions
   486       </p>
   487       <p>
   488         A <a
   489         href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve#Cubic_B.C3.A9zier_curves">cubic
   490         B&eacute;zier curve</a> is defined by four control points, P<sub>0</sub>
   491         through P<sub>3</sub> (see Figure 1). P<sub>0</sub> and P<sub>3</sub>
   492         are always set to (0,0) and (1,1). The 'transition-timing-function' property is used
   493         to specify the values for points P<sub>1</sub> and P<sub>2</sub>. These
   494         can be set to preset values using the keywords listed below, or can be
   495         set to specific values using the ''cubic-bezier'' function.
   496         In the ''cubic-bezier'' function, P<sub>1</sub> and
   497         P<sub>2</sub> are each specified by both an X and Y value.
   498       </p>
   499       <div class="figure">
   500         <img src="TimingFunction.png" alt="The B&eacute;zier timing function is a
   501           smooth curve from point P0 = (0,0) to point P3 = (1,1). The
   502           length and orientation of the line segment P0-P1 determines
   503           the tangent and the curvature of the curve at P0 and the
   504           line segment P2-P3 does the same at P3.">
   505       </div>
   506       <p class="caption">
   507         B&eacute;zier Timing Function Control Points
   508       </p>
   509       <table class="propdef">
   510         <tbody>
   511           <tr>
   512             <th>
   513               Name:
   514             </th>
   515             <td>
   516               <dfn id="transition-timing-function">transition-timing-function</dfn>
   517             </td>
   518           </tr>
   519           <tr>
   520             <th>
   521               Value:
   522             </th>
   523             <td>
   524               <span>&lt;single-transition-timing-function&gt;</span> [ ',' <span>&lt;single-transition-timing-function&gt;</span> ]*
   525             </td>
   526           </tr>
   527           <tr>
   528             <th>
   529               Initial:
   530             </th>
   531             <td>
   532               ease
   533             </td>
   534           </tr>
   535           <tr>
   536             <th>
   537               Applies to:
   538             </th>
   539             <td>
   540               all elements, :before and :after pseudo elements
   541             </td>
   542           </tr>
   543           <tr>
   544             <th>
   545               Inherited:
   546             </th>
   547             <td>
   548               no
   549             </td>
   550           </tr>
   551           <tr>
   552             <th>
   553               Animatable:
   554             </th>
   555             <td>
   556               no
   557             </td>
   558           </tr>
   559           <tr>
   560             <th>
   561               Percentages:
   562             </th>
   563             <td>
   564               N/A
   565             </td>
   566           </tr>
   567           <tr>
   568             <th>
   569               Media:
   570             </th>
   571             <td>
   572               interactive
   573             </td>
   574           </tr>
   575           <tr>
   576             <th>
   577               Computed value:
   578             </th>
   579             <td>
   580               Same as specified value.
   581             </td>
   582           </tr>
   583           <tr>
   584             <th>
   585               Canonical order:
   586             </th>
   587             <td>
   588               <abbr title="follows order of property value definition">per grammar</abbr>
   589             </td>
   590           </tr>
   591         </tbody>
   592       </table>
   593       <div class="prod">
   594         <dfn id="single-transition-timing-function">&lt;single-transition-timing-function&gt;</dfn> = ease | linear | ease-in | ease-out | ease-in-out | step-start | step-end | steps(&lt;integer&gt;[, [ start | end ] ]?) | cubic-bezier(&lt;number&gt;, &lt;number&gt;, &lt;number&gt;, &lt;number&gt;)
   595       </div>
   596       <p>
   597         The timing functions have the following definitions.
   598       </p>
   599       <dl>
   600         <dt>
   601           ease
   602         </dt>
   603         <dd>
   604           The ease function is equivalent to cubic-bezier(0.25, 0.1, 0.25, 1).
   605         </dd>
   606         <dt>
   607           linear
   608         </dt>
   609         <dd>
   610           The linear function is equivalent to cubic-bezier(0, 0, 1, 1).
   611         </dd>
   612         <dt>
   613           ease-in
   614         </dt>
   615         <dd>
   616           The ease-in function is equivalent to cubic-bezier(0.42, 0, 1, 1).
   617         </dd>
   618         <dt>
   619           ease-out
   620         </dt>
   621         <dd>
   622           The ease-out function is equivalent to cubic-bezier(0, 0, 0.58, 1).
   623         </dd>
   624         <dt>
   625           ease-in-out
   626         </dt>
   627         <dd>
   628           The ease-in-out function is equivalent to cubic-bezier(0.42, 0, 0.58, 1)
   629         </dd>
   630         <dt>
   631           step-start
   632         </dt>
   633         <dd>
   634           The step-start function is equivalent to steps(1, start).
   635         </dd>
   636         <dt>
   637           step-end
   638         </dt>
   639         <dd>
   640           The step-end function is equivalent to steps(1, end).
   641         </dd>
   642         <dt>
   643           steps(&lt;integer&gt;[, [ start | end ] ]?)
   644         </dt>
   645         <dd>
   646           Specifies a stepping function, described above, taking two
   647           parameters. The first parameter specifies the number of intervals
   648           in the function. It must be a positive integer (greater than 0).
   649           The second parameter, which is optional, is
   650           either the value ''start'' or ''end'', and specifies the point
   651           at which the change of values occur within the interval.
   652           If the second parameter is omitted, it is given the value ''end''.
   653         </dd>
   654         <dt>
   655           cubic-bezier(&lt;number&gt;, &lt;number&gt;, &lt;number&gt;, &lt;number&gt;)
   656         </dt>
   657         <dd>
   658           Specifies a <a
   659           href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve">cubic-bezier
   660           curve</a>. The four values specify points P<sub>1</sub> and
   661           P<sub>2</sub> of the curve as (x1, y1, x2, y2). Both x values must be
   662           in the range [0, 1] or the definition is invalid. The y values can
   663           exceed this range.
   664         </dd>
   665       </dl><!-- ======================================================================================================= -->
   666       <h3 id="transition-delay-property"><a title="" id="the-transition-delay-property-">
   667         The 'transition-delay' Property
   668       </a></h3>
   669       <p>
   670         The 'transition-delay' property defines when the transition will start. It allows a transition to begin execution some some period of time from when it is applied. A 'transition-delay' value of ''0s'' means the transition will execute as soon as the property is changed. Otherwise, the value specifies an offset from the moment the property is changed, and the transition will delay execution by that offset.
   671       </p>
   672       <p>
   673         If the value for 'transition-delay' is a negative time offset then the transition will execute the moment the property is changed, but will appear to have begun execution at the specified offset. That is, the transition will appear to begin part-way through its play cycle. In the case where a transition has implied starting values and a negative 'transition-delay', the starting values are taken from the moment the property is changed.
   674       </p>
   675       <table class="propdef">
   676         <tbody>
   677           <tr>
   678             <th>
   679               Name:
   680             </th>
   681             <td>
   682               <dfn id="transition-delay">transition-delay</dfn>
   683             </td>
   684           </tr>
   685           <tr>
   686             <th>
   687               Value:
   688             </th>
   689             <td>
   690               <span>&lt;time&gt;</span> [, <span>&lt;time&gt;</span>]*
   691             </td>
   692           </tr>
   693           <tr>
   694             <th>
   695               Initial:
   696             </th>
   697             <td>
   698               0s
   699             </td>
   700           </tr>
   701           <tr>
   702             <th>
   703               Applies to:
   704             </th>
   705             <td>
   706               all elements, :before and :after pseudo elements
   707             </td>
   708           </tr>
   709           <tr>
   710             <th>
   711               Inherited:
   712             </th>
   713             <td>
   714               no
   715             </td>
   716           </tr>
   717           <tr>
   718             <th>
   719               Animatable:
   720             </th>
   721             <td>
   722               no
   723             </td>
   724           </tr>
   725           <tr>
   726             <th>
   727               Percentages:
   728             </th>
   729             <td>
   730               N/A
   731             </td>
   732           </tr>
   733           <tr>
   734             <th>
   735               Media:
   736             </th>
   737             <td>
   738               interactive
   739             </td>
   740           </tr>
   741           <tr>
   742             <th>
   743               Computed value:
   744             </th>
   745             <td>
   746               Same as specified value.
   747             </td>
   748           </tr>
   749           <tr>
   750             <th>
   751               Canonical order:
   752             </th>
   753             <td>
   754               <abbr title="follows order of property value definition">per grammar</abbr>
   755             </td>
   756           </tr>
   757         </tbody>
   758       </table><!-- ======================================================================================================= -->
   759       <h3 id="transition-shorthand-property"><a title="" id="the-transition-shorthand-property-">
   760         The 'transition' Shorthand Property
   761       </a></h3>
   762       <p>
   763         The 'transition' shorthand property combines the four properties described above into a single property.
   764       </p>
   765       <table class="propdef">
   766         <tbody>
   767           <tr>
   768             <th>
   769               Name:
   770             </th>
   771             <td>
   772               <dfn id="transition">transition</dfn>
   773             </td>
   774           </tr>
   775           <tr>
   776             <th>
   777               Value:
   778             </th>
   779             <td>
   780               <span>&lt;single-transition&gt;</span> [ ',' <span>&lt;single-transition&gt;</span> ]*
   781             </td>
   782           </tr>
   783           <tr>
   784             <th>
   785               Initial:
   786             </th>
   787             <td>
   788               see individual properties
   789             </td>
   790           </tr>
   791           <tr>
   792             <th>
   793               Applies to:
   794             </th>
   795             <td>
   796               all elements, :before and :after pseudo elements
   797             </td>
   798           </tr>
   799           <tr>
   800             <th>
   801               Inherited:
   802             </th>
   803             <td>
   804               no
   805             </td>
   806           </tr>
   807           <tr>
   808             <th>
   809               Animatable:
   810             </th>
   811             <td>
   812               no
   813             </td>
   814           </tr>
   815           <tr>
   816             <th>
   817               Percentages:
   818             </th>
   819             <td>
   820               N/A
   821             </td>
   822           </tr>
   823           <tr>
   824             <th>
   825               Media:
   826             </th>
   827             <td>
   828               interactive
   829             </td>
   830           </tr>
   831           <tr>
   832             <th>
   833               Computed value:
   834             </th>
   835             <td>
   836               see individual properties
   837             </td>
   838           </tr>
   839           <tr>
   840             <th>
   841               Canonical order:
   842             </th>
   843             <td>
   844               <abbr title="follows order of property value definition">per grammar</abbr>
   845             </td>
   846           </tr>
   847         </tbody>
   848       </table>
   850       <div class="prod">
   851         <dfn id="single-transition">&lt;single-transition&gt;</dfn> = [ none | <span>&lt;single-transition-property&gt;</span> ] || <span>&lt;time&gt;</span> || <span>&lt;single-transition-timing-function&gt;</span> || <span>&lt;time&gt;</span>
   852       </div>
   854       <p>
   855         Note that order is important within the items in this property:
   856         the first value that can be parsed as a time is assigned to the
   857         transition-duration,
   858         and the second value that can be parsed as a time is assigned to
   859         transition-delay.
   860       </p>
   862       <p>
   863         If there is more than one <span>&lt;single-transition&gt;</span> in the shorthand,
   864         and any of the transitions has
   865         ''none'' as the <span>&lt;single-transition-property&gt;</span>,
   866         then the declaration is invalid.
   867       </p>
   869       <h2 id="starting">
   870         Starting of transitions
   871       </h2>
   873       <p>
   874         When the computed value of an animatable property changes,
   875         implementations must decide what transitions to start based on
   876         the values of the 'transition-property', 'transition-duration',
   877         'transition-timing-function', and 'transition-delay' properties
   878         at the time the animatable property would first have its new
   879         computed value.
   880         This means that when one of these 'transition-*' properties
   881         changes at the same time as
   882         a property whose change might transition,
   883         it is the <em>new</em> values of the 'transition-*' properties
   884         that control the transition.
   885       </p>
   886       <div class="example" id="manual-reversing-example">
   887         <p style="display:none">
   888           Example(s):
   889         </p>
   890         <p>This provides a way for authors to specify different values
   891         of the 'transition-*' properties for the &ldquo;forward&rdquo;
   892         and &ldquo;reverse&rdquo; transitions (but see <a
   893         href="#reversing">below</a> for special reversing behavior when
   894         an <em>incomplete</em> transition is interrupted).  Authors can
   895         specify the value of 'transition-duration',
   896         'transition-timing-function', or 'transition-delay' in the same
   897         rule where they specify the value that triggers the transition,
   898         or can change these properties at the same time as they change
   899         the property that triggers the transition.  Since it's the new
   900         values of these 'transition-*' properties that affect the
   901         transition, these values will be used for the transitions
   902         <em>to</em> the associated transitioning values.  For example:
   903          </p>
   904         <pre>li {
   905   transition: background-color linear 1s;
   906   background: blue;
   907 }
   908 li:hover {
   909   background-color: green;
   910   transition-duration: 2s; /* applies to the transition *to* the :hover state */
   911 }</pre>
   912         <p>
   913           When a list item with these style rules enters the :hover
   914           state, the computed 'transition-duration' at the time that
   915           'background-color' would have its new value (''green'') is ''2s'',
   916           so the transition from ''blue'' to ''green'' takes 2 seconds.
   917           However, when the list item leaves the :hover state, the
   918           transition from ''green'' to ''blue'' takes 1 second.
   919         </p>
   920       </div>
   922       <p>
   923         Various things can cause the computed style of an element to change,
   924         or for an element to start or stop having computed style.
   925         (For the purposes of this specification,
   926         an element has computed style when it is in the document tree,
   927         and does not have computed style when it is not in the document tree.)
   928         These include
   929         insertion and removal of elements from the document tree
   930         (which both changes whether those elements have computed styles and
   931         can change the styles of other elements through selector matching),
   932         changes to the document tree that cause
   933         changes to which selectors match elements,
   934         changes to style sheets or style attributes,
   935         and other things.
   936         This specification does not define when computed styles are updated.
   937         However,
   938         when an implementation updates the computed style for an element
   939         to reflect one of these changes,
   940         it must update the computed style for all elements to reflect all
   941         of these changes at the same time
   942         (or at least it must be undetectable that it was done at a
   943         different time).
   944         This processing of a set of simultaneous style changes is called a
   945         <dfn>style change event</dfn>.
   946         (Implementations typically have a <span>style change event</span> to
   947         correspond with their desired screen refresh rate,
   948         and when up-to-date computed style is needed
   949         for a script API that depends on it.)
   950       </p>
   952       <p>
   953         Since this specification does not define
   954         when a <span>style change event</span> occurs,
   955         and thus what changes to computed values are considered simultaneous,
   956         authors should be aware that changing any of the transition
   957         properties a small amount of time after making a change that
   958         might transition can result in behavior that varies between
   959         implementations, since the changes might be considered
   960         simultaneous in some implementations but not others.
   961       </p>
   963       <p>
   964         When a <span>style change event</span> occurs,
   965         implementations must start transitions based on
   966         the computed styles that changed in that event.
   967         If an element does not have a computed style
   968         either before or after the style change event,
   969         then transitions are not started for that element
   970         in that style change event.
   971         Otherwise,
   972         define the <dfn>before-change style</dfn> as
   973         the computed style for the element as of
   974         the previous <span>style change event</span>,
   975         except with any styles derived from declarative
   976         animations such as CSS Transitions, CSS Animations
   977         ([[CSS3-ANIMATIONS]]),
   978         and SMIL Animations ([[SMIL-ANIMATION]], [[SVG11]])
   979         updated to the current time.
   980         Likewise, define the <dfn>after-change style</dfn> as
   981         the computed style for the element based on the information
   982         known at the start of that <span>style change event</span>,
   983         in other words,
   984         excluding any changes resulting from CSS Transitions
   985         that start during that <span>style change event</span>.
   986       </p>
   988       <p class="issue">
   989         This wording needs to handle already-running transitions better!
   990         Need to cancel a transition that hasn't moved yet when we're
   991         resetting to its start value!  Define canceling as not
   992         firing transition events.  And point to other occurrence of
   993         canceling in reversing section.
   994       </p>
   996       <div class="note">
   997         <p>
   998           Note that this definition of the <span>after-change style</span>
   999           means that a single change
  1000           can start a transition on the same property
  1001           on both an ancestor element and its descendant element.
  1002           This can happen when a property change is inherited
  1003           from one element with 'transition-*' properties
  1004           that say to animate the changing property
  1005           to another element with 'transition-*' properties
  1006           that also say to animate the changing property.
  1007         </p>
  1009         <p>
  1010           When this happens, both transitions will run,
  1011           and the transition on the descendant will override
  1012           the transition on the ancestor
  1013           because of the normal
  1014           CSS cascading and inheritance rules ([[CSS3CASCADE]]).
  1015         </p>
  1017         <p>
  1018           If the transition on the descendant completes before
  1019           the transition on the ancestor,
  1020           the descendant will then resume inheriting
  1021           the (still transitioning) value from its parent.
  1022           This effect is likely not a desirable effect,
  1023           but it is essentially doing what the author asked for.
  1024         </p>
  1025       </div>
  1027       <p>
  1028         For each element with a <span>before-change style</span> and
  1029         an <span>after-change style</span>,
  1030         and each property (other than shorthands) for which
  1031         the <span>before-change style</span> is different from
  1032         the <span>after-change style</span>,
  1033         implementations must
  1034         start transitions based on the relevant item (see <a
  1035         href="#transition-property">the definition of
  1036         'transition-property'</a>) in the computed value of
  1037         'transition-property'.
  1038         Corresponding to this item there is
  1039         a <span>matching transition duration</span>,
  1040         a <span>matching transition delay</span>, and
  1041         a <span>matching transition timing function</span>
  1042         in the computed values of
  1043         'transition-duration', 'transition-delay', and 'transition-timing-function'
  1044         (see <a href="#list-matching">the rules on matching lists</a>).
  1045         Define the <dfn>combined duration</dfn> of the transition
  1046         as the sum of max(matching transition duration, ''0s'') and
  1047         the matching transition-delay.
  1048         When the combined duration is greater than ''0s'',
  1049         then a transition starts based on the values of the
  1050         matching transition duration, the matching transition delay,
  1051         and the matching transition-timing-function;
  1052         in other cases transitions do not occur.
  1053         The <dfn>start time</dfn> of this transition is defined as
  1054         the time of the <span>style change event</span> plus
  1055         the matching transition delay.
  1056         The <dfn>end time</dfn> of this transition is defined as
  1057         the <span>start time</span> plus the matching transition duration.
  1058         The <dfn>start value</dfn> of this transition is defined as
  1059         the value of the transitioning property
  1060         in the <span>before-change style</span>,
  1061         and the <dfn>end value</dfn> of this transition is defined as
  1062         the value of the transitioning property
  1063         in the <span>after-change style</span>.
  1064         Except in the cases described
  1065         in the <a href="#reversing">section on reversing of
  1066         transitions</a>,
  1067         the <dfn>reversing-adjusted start value</dfn> is the same as
  1068         the <span>start value</span>,
  1069         and the <dfn>reversing shortening factor</dfn> is 1.
  1070       </p>
  1072       <p>
  1073         Once the transition of a property has started, it must continue
  1074         running based on the original timing function, duration, and
  1075         delay, even if the 'transition-timing-function',
  1076         'transition-duration', or 'transition-delay' property changes
  1077         before the transition is complete.  However, if the
  1078         'transition-property' property changes such that the transition
  1079         would not have started, the transition must stop (and the
  1080         property must immediately change to its final value).
  1081       </p>
  1083       <p>
  1084         Implementations must not start a transition when the computed
  1085         value of a property changes as a result of declarative animation
  1086         (as opposed to scripted animation).
  1087       </p>
  1089       <p>
  1090         Implementations also must not start a transition when the
  1091         computed value changes because it is inherited (directly or
  1092         indirectly) from another element that is transitioning the same
  1093         property.
  1094       </p>
  1096       <h3 id="reversing">
  1097         Faster reversing of interrupted transitions
  1098       </h3>
  1099       <p>
  1100         Many common transitions effects involve transitions between two states,
  1101         such as the transition that occurs when the mouse pointer moves
  1102         over a user interface element, and then later moves out of that element.
  1103         With these effects, it is common for a running transition
  1104         to be interrupted before it completes,
  1105         and the property reset to the starting value of that transition.
  1106         An example is a hover effect on an element,
  1107         where a transition starts when the pointer enters the element,
  1108         and then the pointer exits the element before the effect has completed.
  1109         If the outgoing and incoming transitions
  1110         are executed using their specified durations and timing functions,
  1111         the resulting effect can be distractingly asymmetric
  1112         because the second transition
  1113         takes the full specified time to move a shortened distance.
  1114         Instead, the expected behavior is that the second transition is shorter.
  1115       </p>
  1117       <p>
  1118         To meet this expectation,
  1119         when a transition is started for a property on an element
  1120         (henceforth, the <dfn>new transition</dfn>)
  1121         that has a currently-running transition whose
  1122         <span>reversing-adjusted start value</span> is the same as the
  1123         <span>end value</span> of the new transition
  1124         (henceforth, the <dfn>old transition</dfn>), implementations
  1125         must cancel the old transition <span class="issue">link to
  1126         definition above</span> and adjust the new transition as follows
  1127         (prior to following the rules for computing the <span>combined
  1128         duration</span>, <span>start time</span>, and <span>end
  1129         time</span>):
  1130       </p>
  1132       <ol>
  1134         <li>
  1135           The <span>reversing-adjusted start value</span> of the new
  1136           transition is instead the the <span>end value</span> of the
  1137           old transition.
  1138           <span class="note">Note: This represents the logical start state of
  1139           the transition, and allows some calculations to ignore that
  1140           the transition started before that state was reached, which
  1141           in turn allows repeated reversals of the same transition to
  1142           work correctly.</span>
  1143         </li>
  1145         <li>
  1146           The <span>reversing shortening factor</span> of the new
  1147           transition is the absolute value, clamped to the range [0, 1],
  1148           of the sum of:
  1149           <ol>
  1150             <li>the output of the timing function of the old transition
  1151             at the time of the <span>style change event</span>,
  1152             times the <span>reversing shortening factor</span> of the
  1153             old transition</li>
  1154             <li>1 minus the <span>reversing shortening factor</span> of
  1155             the old transition.</li>
  1156           </ol>
  1157           <span class="note">Note: This represents the portion of the
  1158           space between the <span>reversing-adjusted start value</span>
  1159           and the <span>end value</span> that the old transition has
  1160           traversed (in amounts of the value, not time), except with the
  1161           absolute value and clamping to handle timing functions that
  1162           have y1 or y2 outside the range [0, 1].</span>
  1163         </li>
  1165         <li>
  1166           The matching transition-duration for the new transition is
  1167           multiplied by the
  1168           <span>reversing shortening factor</span>.
  1169         </li>
  1171         <li>
  1172           If the matching transition-delay for the new transition is
  1173           negative, it is also multiplied by the
  1174           <span>reversing shortening factor</span>.
  1175         </li>
  1177       </ol>
  1179       <p class="note">
  1180         Note that these rules do not fully address the problem for
  1181         transition patterns that involve more than two states.
  1182       </p>
  1184       <p class="note">
  1185         Note that these rules lead to the entire timing function of the
  1186         new transition being used, rather than jumping into the middle
  1187         of a timing function, which can create a jarring effect.
  1188       </p>
  1190       <p class="note">
  1191         This was one of several possibilities that was considered by the
  1192         working group.  See the
  1193         <a href="transition-reversing-demo">reversing demo</a>
  1194         demonstrating a number of them, leading to a working group
  1195         resolution made on 2013-06-07 and edits made on 2013-11-11.
  1196       </p>
  1198       <h2 id="application">
  1199         Application of transitions
  1200       </h2>
  1202       <p>
  1203         When a property on an element is undergoing a transition
  1204         (that is, when or after the transition has started and before the
  1205         <span>end time</span> of the transition)
  1206         the transition adds a style to the CSS cascade
  1207         at the level defined for CSS Transitions in [[CSS3CASCADE]].
  1208       </p>
  1210       <p class="note">
  1211         Note that this means that computed values
  1212         resulting from CSS transitions
  1213         can inherit to descendants just like
  1214         any other computed values.
  1215         In the normal case, this means that
  1216         a transition of an inherited property
  1217         applies to descendant elements
  1218         just as an author would expect.
  1219       </p>
  1221       <p>
  1222         Implementations must add this value to the cascade
  1223         if and only if
  1224         that property is not currently
  1225         undergoing a CSS Animation ([[CSS3-ANIMATIONS]]) on the same element.
  1226       </p>
  1228       <p class="note">
  1229         Note that this behavior of transitions not applying to the cascade
  1230         when an animation on the same element and property is running
  1231         does not affect whether the transition has started or ended.
  1232         APIs that detect whether transitions are running
  1233         (such as <a href="#transition-events">transition events</a>)
  1234         still report that a transition is running.
  1235       </p>
  1237       <p>
  1238         If the current time is at or before the
  1239         <span>start time</span> of the transition
  1240         (that is, during the delay phase of the transition),
  1241         this value is a specified style that will compute
  1242         to the <span>start value</span> of the transition.
  1243       </p>
  1245       <p>
  1246         If the current time is after the
  1247         <span>start time</span> of the transition
  1248         (that is, during the duration phase of the transition),
  1249         this value is a specified style that will compute
  1250         to the <a href="#animatable-types">result of interpolating the property</a>
  1251         using the <span>start value</span> of the transition as
  1252         <var>V</var><sub>start</sub>,
  1253         using the <span>end value</span> of the transition as
  1254         <var>V</var><sub>end</sub>,
  1255         and using (current time - start time) / (end time - start time)
  1256         as the input to the timing function.
  1257       </p>
  1259       <h2 id="transition-events"><a title="" id="transition-events-">
  1260         Transition Events
  1261       </a></h2>
  1262       <p>
  1263         The completion of a CSS Transition generates a corresponding <a href="http://www.w3.org/TR/DOM-Level-2-Events/events.html">DOM Event</a>.
  1264         An event is fired for each property that undergoes a transition.
  1265         This allows a content developer to perform actions that synchronize
  1266         with the completion of a transition.
  1267       </p>
  1268       <p>
  1269         Each event provides the name of the property the transition is
  1270         associated with as well as the duration of the transition.
  1271       </p>
  1272       <dl>
  1273         <dt>
  1274           <b>Interface <dfn id="Events-TransitionEvent">TransitionEvent</dfn></b>
  1275         </dt>
  1276         <dd>
  1277           <p>
  1278             The <code>TransitionEvent</code> interface provides specific contextual information associated with transitions.
  1279           </p>
  1280           <dl>
  1281             <dt>
  1282               <b>IDL Definition</b>
  1283             </dt>
  1284             <dd>
  1285               <div class='idl-code'>
  1286                 <pre>
  1287   <span id="TransitionEvent">[Constructor(DOMString <var title="">type</var>, optional <i>TransitionEventInit</i> <var title="">transitionEventInitDict</var>)]
  1288   interface TransitionEvent</span> : Event {
  1289     readonly attribute DOMString          <a href="#Events-TransitionEvent-propertyName">propertyName</a>;
  1290     readonly attribute float              <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a>;
  1291     readonly attribute DOMString          <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a>;
  1292   };
  1294   dictionary <dfn id="TransitionEventInit">TransitionEventInit</dfn> : <a class="external" href="https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#eventinit">EventInit</a> {
  1295     DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a> = "";
  1296     float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a> = 0.0;
  1297     DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a> = "";
  1299   </pre>
  1300               </div>
  1301             </dd>
  1302             <dt>
  1303               <b>Attributes</b>
  1304             </dt>
  1305             <dd>
  1306               <dl>
  1307                 <dt>
  1308                   <code class='attribute-name'><dfn title="TransitionEvent::propertyName" id="Events-TransitionEvent-propertyName">propertyName</dfn></code> of type <code>DOMString</code>, readonly
  1309                 </dt>
  1310                 <dd>
  1311                   The name of the CSS property associated with the transition.
  1312                 </dd>
  1313               </dl>
  1314               <dl>
  1315                 <dt>
  1316                   <code class='attribute-name'><dfn title="TransitionEvent::elapsedTime" id="Events-TransitionEvent-elapsedTime">elapsedTime</dfn></code> of type <code>float</code>, readonly
  1317                 </dt>
  1318                 <dd>
  1319                   The amount of time the transition has been running, in seconds, when this event fired. Note that this value is not affected by the value of <code class="property">transition-delay</code>.
  1320                 </dd>
  1321               </dl>
  1322               <dl>
  1323                 <dt>
  1324                   <code class='attribute-name'><dfn title="TransitionEvent::pseudoElement" id="Events-TransitionEvent-pseudoElement">pseudoElement</dfn></code> of type <code>DOMString</code>, readonly
  1325                 </dt>
  1326                 <dd>
  1327                   The name (beginning with two colons) of the CSS
  1328                   pseudo-element on which the transition occurred (in
  1329                   which case the target of the event is that
  1330                   pseudo-element's corresponding element), or the empty
  1331                   string if the transition occurred on an element (which
  1332                   means the target of the event is that element).
  1333                 </dd>
  1334               </dl>
  1335             </dd>
  1336           </dl>
  1337           <p>
  1338             <code id="TransitionEvent-constructor">TransitionEvent(type, transitionEventInitDict)</code>
  1339             is an <a class="external" href="https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#constructing-events">event constructor</a>.
  1340           </p>
  1341         </dd>
  1342       </dl>
  1343       <p>
  1344         There is one type of transition event available.
  1345       </p>
  1346       <dl>
  1347         <dt>
  1348           <b><dfn>transitionend</dfn></b>
  1349         </dt>
  1350         <dd>
  1351           The <code>transitionend</code> event occurs at the completion of the transition. In the
  1352           case where a transition is removed before completion, such as if the
  1353           transition-property is removed, then the event will not fire.
  1354           <ul>
  1355             <li>Bubbles: Yes
  1356             </li>
  1357             <li>Cancelable: No
  1358             </li>
  1359             <li>Context Info: propertyName, elapsedTime, pseudoElement
  1360             </li>
  1361           </ul>
  1362         </dd>
  1363       </dl>
  1365       <h2 id="animatable-types"><a title="" id="animation-of-property-types-">
  1366         Animation of property types
  1367       </a></h2>
  1369       <p>
  1370         When interpolating between two values,
  1371         <var>V</var><sub>start</sub> and <var>V</var><sub>end</sub>,
  1372         interpolation is done using the output <var>p</var> of the timing function,
  1373         which gives the portion of the value space
  1374         that the interpolation has crossed.
  1375         Thus the result of the interpolation is
  1376         <var>V</var><sub>res</sub> =
  1377           (1 - <var>p</var>) &sdot; <var>V</var><sub>start</sub> +
  1378           <var>p</var> &sdot; <var>V</var><sub>end</sub>.
  1379       </p>
  1381       <p>
  1382         However, if this value (<var>V</var><sub>res</sub>)
  1383         is outside the allowed range of values for the property,
  1384         then it is clamped to that range.
  1385         This can occur if <var>p</var> is outside of the range 0 to 1,
  1386         which can occur if a timing function is specified
  1387         with a <var>y1</var> or <var>y2</var> that is outside the range 0 to 1.
  1388       </p>
  1390       <p>
  1391         The following describes how each property type undergoes transition or
  1392         animation.
  1393       </p>
  1395       <ul>
  1396         <li id="animtype-color">
  1397           <strong>color</strong>: interpolated via red, green, blue and alpha
  1398           components (treating each as a number, see below).
  1399           The interpolation is done between premultiplied colors
  1400           (that is, colors for which the red, green, and blue components
  1401           specified have been multiplied by the alpha).
  1402         </li>
  1403         <li id="animtype-length">
  1404           <strong>length</strong>: interpolated as real numbers.
  1405         </li>
  1406         <li id="animtype-percentage">
  1407           <strong>percentage</strong>: interpolated as real numbers.
  1408         </li>
  1409         <li id="animtype-lpcalc">
  1410           <strong>length, percentage, or calc</strong>: when both values
  1411           are lengths, interpolated as lengths; when both values are
  1412           percentages, interpolated as percentages; otherwise, both
  1413           values are converted into a ''calc()'' function that is the
  1414           sum of a length and a percentage (each possibly zero), and
  1415           these ''calc()'' functions have each half interpolated as real
  1416           numbers.
  1417         </li>
  1418         <li id="animtype-integer">
  1419           <strong>integer</strong>: interpolated via discrete steps (whole
  1420           numbers). The interpolation happens in real number space and is
  1421           converted to an integer by rounding to the nearest integer, with
  1422           values halfway between a pair of integers rounded towards
  1423           positive infinity.
  1424         </li>
  1425         <li id="animtype-font-weight">
  1426           <strong>font weight</strong>: interpolated via discrete steps
  1427           (multiples of 100). The interpolation happens in real number
  1428           space and is converted to an integer by rounding to the
  1429           nearest multiple of 100, with values halfway between multiples
  1430           of 100 rounded towards positive infinity.
  1431         </li>
  1432         <li id="animtype-number">
  1433           <strong>number</strong>: interpolated as real (floating point)
  1434           numbers.
  1435         </li>
  1436         <li id="animtype-rect">
  1437           <strong>rectangle</strong>: interpolated via the x, y,
  1438           width and height components (treating each as a number).
  1439         </li>
  1440         <li id="animtype-visibility">
  1441           <strong>visibility</strong>: if one of the values is
  1442           ''visible'', interpolated as a discrete step where values of the
  1443           timing function between 0 and 1 map to ''visible'' and other
  1444           values of the timing function (which occur only at the
  1445           start/end of the transition or as a result of ''cubic-bezier()''
  1446           functions with Y values outside of [0, 1]) map to the closer
  1447           endpoint; if neither value is ''visible'' then not interpolable.
  1448         </li>
  1449         <li id="animtype-shadow-list">
  1450           <strong>shadow list</strong>: Each shadow in the list is
  1451           interpolated via the
  1452           color (as <a href="#animtype-color">color</a>) component,
  1453           and x, y, blur, and (when appropriate) spread
  1454           (as <a href="#animtype-length">length</a>) components.
  1455           For each shadow, if one input shadow is ''inset'' and the other
  1456           is not, then the result for that shadow matches the inputs;
  1457           otherwise the entire list is not interpolable.
  1458           If the lists of shadows have different lengths,
  1459           then the shorter list is padded at the end
  1460           with shadows whose color is ''transparent'',
  1461           all lengths are ''0'',
  1462           and whose ''inset'' (or not) matches the longer list.
  1463         </li>
  1464         <li id="animtype-gradient">
  1465           <strong>gradient</strong>: interpolated via the
  1466           positions and colors of each stop. They must have the same type
  1467           (radial or linear) and same number of stops in order to be animated.
  1468           <span class="note">Note: [[CSS3-IMAGES]] may extend this
  1469           definition.</span>
  1470         </li>
  1471         <li id="animtype-paintserver">
  1472           <strong>paint server</strong> (SVG): interpolation is only supported
  1473           between: gradient to gradient and color to color. They then
  1474           work as above.
  1475         </li>
  1476         <li id="animtype-simple-list">
  1477           <strong>simple list</strong> of other types:
  1478           If the lists have the same number of items,
  1479           and each pair of values can be interpolated,
  1480           each item in the list is interpolated using
  1481           the rules given for those types.
  1482           Otherwise the values are not interpolable.
  1483         </li>
  1484         <li id="animtype-repeatable-list">
  1485           <strong>repeatable list</strong> of other types:
  1486           The result list has a length that is the least common multiple
  1487           of the lengths of the input lists.
  1488           Each item in the result is the interpolation of the value
  1489           from each input list repeated to the length of the result list.
  1490           If a pair of values cannot be interpolated, then the lists
  1491           are not interpolable.
  1492           <span class="note">
  1493             The repeatable list concept ensures that a list that is
  1494             conceptually repeated to a certain length (as
  1495             'background-origin' is repeated to the length of the
  1496             'background-image' list) or repeated infinitely will
  1497             smoothly transition between any values, and so that the
  1498             computed value will properly represent the result (and
  1499             potentially be inherited correctly).
  1500           </span>
  1501         </li>
  1502       </ul>
  1504       <p>Future specifications may define additional types that can
  1505       be animated.</p>
  1507       <p>See the definition of 'transition-property' for how animation
  1508       of shorthand properties and the ''all'' value is applied to any
  1509       properties (in the shorthand) that can be animated.</p>
  1511       <h2 id="animatable-properties"><a title="" id="animatable-properties-">
  1512         Animatable properties
  1513       </a></h2>
  1515       <!--
  1516       As resolved in
  1517       http://lists.w3.org/Archives/Public/www-style/2011Sep/0497.html
  1518       -->
  1520       <p>The definition of each CSS property defines
  1521       when the values of that property can be interpolated
  1522       by referring to the definitions of property types
  1523       in the <a href="#animatable-types">previous section</a>.
  1524       Values are animatable when
  1525       both the from and the to values of the property have the type described.
  1526       (When a composite type such as "length, percentage, or calc" is listed,
  1527       this means that both values must fit into that composite type.)
  1528       When multiple types are listed in the form "either A or B",
  1529       both values must be of the same type to be interpolable.</p>
  1531       <p>For properties that exist at the time this specification was
  1532       developed, this specification defines whether and how they are
  1533       animated.  However, future CSS specifications may define
  1534       additional properties, additional values for existing properties,
  1535       or additional animation behavior of existing values.  In order to
  1536       describe new animation behaviors and to have the definition of
  1537       animation behavior in a more appropriate location, future CSS
  1538       specifications should include an "Animatable:" line in the summary
  1539       of the property's definition (in addition to the other lines
  1540       described in [[CSS21]], <a
  1541       href="http://www.w3.org/TR/CSS21/about.html#property-defs">section
  1542       1.4.2</a>).  This line should say "no" to indicate that a property
  1543       cannot be animated or should reference an animation behavior
  1544       (which may be one of the behaviors in the <a
  1545       href="#animation-of-property-types-">Animation of property
  1546       types</a> section above, or may be a new behavior) to define how
  1547       the property animates.  Such definitions override those given in
  1548       this specification.</p>
  1550       <h3 id="animatable-css"><a title="" id="properties-from-css-">
  1551         Properties from CSS
  1552       </a></h3>
  1554       <p>
  1555       The following definitions define the animation behavior for
  1556       properties in CSS Level 2 Revision 1 ([[CSS21]]) and in Level 3 of
  1557       the CSS Color Module ([[CSS3COLOR]]).
  1558       </p>
  1560      <table class="animatable-properties">
  1561        <tr>
  1562          <th>Property Name</th>
  1563          <th>Type</th>
  1564        </tr>
  1565        <tr>
  1566          <td>background-color</td><td>as <a href="#animtype-color">color</a></tr>
  1567        <tr>
  1568          <td>background-position</td><td>as <a href="#animtype-repeatable-list">repeatable list</a> of <a href="#animtype-simple-list">simple list</a> of <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1569        </tr>
  1570        <tr>
  1571          <td>border-bottom-color</td><td>as <a href="#animtype-color">color</a></td>
  1572        </tr>
  1573        <tr>
  1574          <td>border-bottom-width</td><td>as <a href="#animtype-length">length</a></td>
  1575        </tr>
  1576        <tr>
  1577          <td>border-left-color</td><td>as <a href="#animtype-color">color</a></td>
  1578        </tr>
  1579        <tr>
  1580          <td>border-left-width</td><td>as <a href="#animtype-length">length</a></td>
  1581        </tr>
  1582        <tr>
  1583          <td>border-right-color</td><td>as <a href="#animtype-color">color</a></td>
  1584        </tr>
  1585        <tr>
  1586          <td>border-right-width</td><td>as <a href="#animtype-length">length</a></td>
  1587        </tr>
  1588        <tr>
  1589          <td>border-spacing</td><td>as <a href="#animtype-simple-list">simple list</a> of <a href="#animtype-length">length</a></td>
  1590        </tr>
  1591        <tr>
  1592          <td>border-top-color</td><td>as <a href="#animtype-color">color</a></td>
  1593        </tr>
  1594        <tr>
  1595          <td>border-top-width</td><td>as <a href="#animtype-length">length</a></td>
  1596        </tr>
  1597        <tr>
  1598          <td>bottom</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1599        </tr>
  1600        <tr>
  1601          <td>clip</td><td>as <a href="#animtype-rect">rectangle</a></td>
  1602        </tr>
  1603        <tr>
  1604          <td>color</td><td>as <a href="#animtype-color">color</a></td>
  1605        </tr>
  1606        <tr>
  1607          <td>font-size</td><td>as <a href="#animtype-length">length</a></td>
  1608        </tr>
  1609        <tr>
  1610          <td>font-weight</td><td>as <a href="#animtype-font-weight">font weight</a></td>
  1611        </tr>
  1612        <tr>
  1613          <td>height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1614        </tr>
  1615        <tr>
  1616          <td>left</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1617        </tr>
  1618        <tr>
  1619          <td>letter-spacing</td><td>as <a href="#animtype-length">length</a></td>
  1620        </tr>
  1621        <tr>
  1622          <td>line-height</td><td>as either <a href="#animtype-number">number</a> or <a href="#animtype-length">length</a></td>
  1623        </tr>
  1624        <tr>
  1625          <td>margin-bottom</td><td>as <a href="#animtype-length">length</a></td>
  1626        </tr>
  1627        <tr>
  1628          <td>margin-left</td><td>as <a href="#animtype-length">length</a></td>
  1629        </tr>
  1630        <tr>
  1631          <td>margin-right</td><td>as <a href="#animtype-length">length</a></td>
  1632        </tr>
  1633        <tr>
  1634          <td>margin-top</td><td>as <a href="#animtype-length">length</a></td>
  1635        </tr>
  1636        <tr>
  1637          <td>max-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1638        </tr>
  1639        <tr>
  1640          <td>max-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1641        </tr>
  1642        <tr>
  1643          <td>min-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1644        </tr>
  1645        <tr>
  1646          <td>min-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1647        </tr>
  1648        <tr>
  1649          <td>opacity</td><td>as <a href="#animtype-number">number</a></td>
  1650        </tr>
  1651        <tr>
  1652          <td>outline-color</td><td>as <a href="#animtype-color">color</a></td>
  1653        </tr>
  1654        <tr>
  1655          <td>outline-width</td><td>as <a href="#animtype-length">length</a></td>
  1656        </tr>
  1657        <tr>
  1658          <td>padding-bottom</td><td>as <a href="#animtype-length">length</a></td>
  1659        </tr>
  1660        <tr>
  1661          <td>padding-left</td><td>as <a href="#animtype-length">length</a></td>
  1662        </tr>
  1663        <tr>
  1664          <td>padding-right</td><td>as <a href="#animtype-length">length</a></td>
  1665        </tr>
  1666        <tr>
  1667          <td>padding-top</td><td>as <a href="#animtype-length">length</a></td>
  1668        </tr>
  1669        <tr>
  1670          <td>right</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1671        </tr>
  1672        <tr>
  1673          <td>text-indent</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1674        </tr>
  1675        <tr>
  1676          <td>text-shadow</td><td>as <a href="#animtype-shadow-list">shadow list</a></td>
  1677        </tr>
  1678        <tr>
  1679          <td>top</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1680        </tr>
  1681        <tr>
  1682          <td>vertical-align</td><td>as <a href="#animtype-length">length</a></td>
  1683        </tr>
  1684        <tr>
  1685          <td>visibility</td><td>as <a href="#animtype-visibility">visibility</a></td>
  1686        </tr>
  1687        <tr>
  1688          <td>width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
  1689        </tr>
  1690        <tr>
  1691          <td>word-spacing</td><td>as <a href="#animtype-length">length</a></td>
  1692        </tr>
  1693        <tr>
  1694          <td>z-index</td><td>as <a href="#animtype-integer">integer</a></td>
  1695        </tr>
  1696      </table>
  1698      <h3 id="animatable-svg"><a title="" id="properties-from-svg-">
  1699        Properties from SVG
  1700      </a></h3>
  1702      <p>
  1703        All properties defined as animatable in the SVG specification, provided
  1704        they are one of the property types listed above.
  1705       </p>
  1707      <!-- <table>
  1708        <tr>
  1709          <th>Property Name</th><th>Type</th>
  1710        </tr>
  1711        <tr>
  1712          <td>stop-color</td><td>as <a href="#animtype-color">color</a></td>
  1713        </tr>
  1714        <tr>
  1715          <td>stop-opacity</td><td>as <a href="#animtype-number">number</a></td>
  1716        </tr>
  1717        <tr>
  1718          <td>fill</td><td>as <a href="#animtype-paintserver">paint server</a></td>
  1719        </tr>
  1720        <tr>
  1721          <td>fill-opacity</td><td>as <a href="#animtype-number">number</a></td>
  1722        </tr>
  1723        <tr>
  1724          <td>stroke</td><td>as <a href="#animtype-paintserver">paint server</a></td>
  1725        </tr>
  1726        <tr>
  1727          <td>stroke-dasharray</td><td>as <a href="#animtype-repeatable-list">repeatable list</a> of <a href="#animtype-number">number</a></td>
  1728        </tr>
  1729        <tr>
  1730          <td>stroke-dashoffset</td><td>as <a href="#animtype-number">number</a></td>
  1731        </tr>
  1732        <tr>
  1733          <td>stroke-miterlimit</td><td>as <a href="#animtype-number">number</a></td>
  1734        </tr>
  1735        <tr>
  1736          <td>stroke-opacity</td><td>as <a href="#animtype-number">number</a></td>
  1737        </tr>
  1738        <tr>
  1739          <td>stroke-width</td><td>as <a href="#animtype-number">number</a></td>
  1740        </tr>
  1741        <tr>
  1742          <td>viewport-fill</td><td>as <a href="#animtype-color">color</a></td>
  1743        </tr>
  1744        <tr>
  1745          <td>viewport-fill-opacity</td><td>as <a href="#animtype-color">color</a></td>
  1746        </tr>
  1747       </table> -->
  1749 <h2 id="changes">Changes since Working Draft of 19 November 2013</h2>
  1751 <p>The following are the substantive changes made since the
  1752 <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20131119/">Working Draft
  1753 dated 19 November 2013</a>:</p>
  1755 <ul>
  1756   <li>The transitionend event is no longer cancelable.  This is since it has no default action, so canceling it would have no meaning.  It also matches the animation events.</p>
  1757   <li class="issue">... ADD CHANGES HERE ...
  1758 </ul>
  1760 <p>For more details on these changes, see the version control <a href="https://dvcs.w3.org/hg/csswg/log/tip/css-transitions/Overview.src.html">change log</a>.</p>
  1762 <p>For changes in earlier working drafts:</p>
  1764 <ol>
  1765   <li>see the <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20131119/#changes">changes section in the 19 November 2013 Working Draft</a>
  1766   <li>see the <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20130212/ChangeLog">the ChangeLog</a> for changes in previous working drafts
  1767   <li>For more details on these changes, see the version control change logs, which are split in two parts because of a file renaming: <a href="https://dvcs.w3.org/hg/csswg/log/tip/css-transitions/Overview.src.html">change log since 2013 March 28</a>, <a href="https://dvcs.w3.org/hg/csswg/log/tip/css3-transitions/Overview.src.html">change log before 2013 March 28</a>.
  1768 </ol>
  1770 <h2 id="acknowledgments">Acknowledgments</h2>
  1772 <p>Thanks especially to the feedback from
  1773 Tab Atkins,
  1774 Carine Bournez,
  1775 Aryeh Gregor,
  1776 Vincent Hardy,
  1777 Anne van Kesteren,
  1778 Cameron McCormack,
  1779 Alex Mogilevsky,
  1780 and all the rest of the
  1781 <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.</p>
  1783 <h2 id="references">References</h2>
  1785 <h3 class="no-num" id="normative-references">Normative references</h3>
  1786 <!--normative-->
  1788 <h3 class="no-num" id="other-references">Other references</h3>
  1789 <!--informative-->
  1793 <h2 class="no-num" id="property-index">Property index</h2>
  1794 <!-- properties -->
  1798 <h2 class="no-num" id="index">Index</h2>
  1799 <!--index-->
  1801 </body>
  1802 </html>
  1803 <!-- Keep this comment at the end of the file
  1804 Local variables:
  1805 mode: sgml
  1806 sgml-default-doctype-name:"html"
  1807 sgml-minimize-attributes:t
  1808 End:
  1809 -->

mercurial