css-transitions/Overview.src.html@3d943f796fee
css-transitions/Overview.src.html
Tue, 22 Oct 2013 11:45:08 +0200
- author
- L. David Baron <dbaron@dbaron.org>
- date
- Tue, 22 Oct 2013 11:45:08 +0200
- changeset 9406
- 3d943f796fee
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- child 9524
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[css-transitions] Note issue with wording of previous large edit.
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/[SHORTNAME]/">http://dev.w3.org/csswg/[SHORTNAME]/</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-20130212/">http://www.w3.org/TR/2013/WD-css3-transitions-20130212/</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><a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Transitions&resolution=---&cmdtype=doit">in Bugzilla</a>
57 <dt>Feedback:
58 <dd><a href="mailto:www-style@w3.org?subject=%5Bcss-transitions%5D%20feedback">www-style@w3.org</a>
59 with subject line “<kbd>[css-transitions] <var>… message topic …</var></kbd>”
60 (<a rel="discussion" href="http://lists.w3.org/Archives/Public/www-style/">archives</a>)
62 <dt>Test suite:
63 <dd> <a href="http://test.csswg.org/suites/css-transitions-1/nightly-unstable/">http://test.csswg.org/suites/css-transitions-1/nightly-unstable/</a>
64 </dl>
66 <!--copyright-->
68 <hr title="Separator for header">
69 </div>
71 <h2 class="no-num no-toc" id="abstract">Abstract</h2>
73 <p>CSS Transitions allows property changes in CSS values to occur smoothly
74 over a specified duration.
76 <h2 class="no-num no-toc" id="status">Status of this document</h2>
77 <!--status-->
79 <h2 class="no-num no-toc" id="contents">Table of Contents</h2>
80 <!--toc-->
83 <h2 id="introduction">Introduction</h2>
85 <p><em>This section is not normative.</em>
86 <p>
87 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.
88 </p>
90 <h2 id="transitions"><a id="transitions-">Transitions</a></h2>
91 <p>
92 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.
93 </p>
94 <p>
95 For example, suppose that transitions of one second have been defined on the 'left' and
96 '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.
97 </p>
98 <div class="figure">
99 <img src="transition1.png" alt="">
100 </div>
101 <p class="caption">
102 Transitions of 'left' and 'background-color'
103 </p>
104 <p>
105 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.
106 </p>
107 <p>
108 Only animatable CSS properties can be transitioned. See the table at the end of this document for a list
109 of properties that are animatable.
110 </p>
111 <p>
112 The transition for a property is defined using a number of new properties. For example:
113 </p>
114 <div class="example">
115 <p style="display:none">
116 Example(s):
117 </p>
118 <pre>
119 div {
120 transition-property: opacity;
121 transition-duration: 2s;
122 }
123 </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.
124 </div>
125 <p>
126 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:
127 </p>
128 <div class="example">
129 <p style="display:none">
130 Example(s):
131 </p>
132 <pre>
133 div {
134 transition-property: opacity, left;
135 transition-duration: 2s, 4s;
136 }
138 </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.
139 </div>
141 <p id="list-matching">
142 In the case where the lists of values in transition properties
143 do not have the same length, the length of the
144 'transition-property' list determines the number of items in
145 each list examined when starting transitions. The lists are
146 matched up from the first value: excess values at the end are
147 not used. If one of the other properties doesn't have enough
148 comma-separated values to match the number of values of
149 'transition-property', the UA must calculate its used value by
150 repeating the list of values until there are enough. This
151 truncation or repetition does not affect the computed value.
152 <span class="note">
153 Note: This is analogous to the behavior of the 'background-*'
154 properties, with 'background-image' analogous to
155 'transition-property'.
156 </span>
157 </p>
159 <div class="example">
160 <p style="display:none">
161 Example(s):
162 </p>
163 <pre>
164 div {
165 transition-property: opacity, left, top, width;
166 transition-duration: 2s, 1s;
167 }
168 </pre>The above example defines a transition on the 'opacity' property of 2 seconds duration, a
169 transition on the 'left' property of 1
170 second duration, a transition on the 'top' property of 2 seconds duration and a
171 transition on the 'width' property of 1
172 second duration.
174 </div>
176 <p>
177 While authors can use transitions to create dynamically changing content,
178 dynamically changing content can lead to seizures in some users.
179 For information on how to avoid content that can lead to seizures, see
180 <a href="http://www.w3.org/TR/WCAG20/#seizure">Guideline 2.3:
181 Seizures:
182 Do not design content in a way that is known to cause seizures</a>
183 ([[WCAG20]]).
184 </p>
186 <!-- ======================================================================================================= -->
187 <h3 id="transition-property-property"><a id="the-transition-property-property-">
188 The 'transition-property' Property
189 </a></h3>
190 <p>
191 The 'transition-property' property specifies the name of the CSS property to which the transition is applied.
192 </p>
193 <table class="propdef">
194 <tbody>
195 <tr>
196 <td>
197 <em>Name:</em>
198 </td>
199 <td>
200 <dfn id="transition-property">transition-property</dfn>
201 </td>
202 </tr>
203 <tr>
204 <td>
205 <em>Value:</em>
206 </td>
207 <td>
208 none | <span><single-transition-property></span> [ ',' <span><single-transition-property></span> ]*
209 </td>
210 </tr>
211 <tr>
212 <td>
213 <em>Initial:</em>
214 </td>
215 <td>
216 all
217 </td>
218 </tr>
219 <tr>
220 <td>
221 <em>Applies to:</em>
222 </td>
223 <td>
224 all elements, :before and :after pseudo elements
225 </td>
226 </tr>
227 <tr>
228 <td>
229 <em>Inherited:</em>
230 </td>
231 <td>
232 no
233 </td>
234 </tr>
235 <tr>
236 <td>
237 <em>Animatable:</em>
238 </td>
239 <td>
240 no
241 </td>
242 </tr>
243 <tr>
244 <td>
245 <em>Percentages:</em>
246 </td>
247 <td>
248 N/A
249 </td>
250 </tr>
251 <tr>
252 <td>
253 <em>Media:</em>
254 </td>
255 <td>
256 visual
257 </td>
258 </tr>
259 <tr>
260 <td>
261 <em>Computed value:</em>
262 </td>
263 <td>
264 Same as specified value.
265 </td>
266 </tr>
267 <tr>
268 <td>
269 <em>Canonical order:</em>
270 </td>
271 <td>
272 <abbr title="follows order of property value definition">per grammar</abbr>
273 </td>
274 </tr>
275 </tbody>
276 </table>
278 <div class="prod">
279 <dfn id="single-transition-property"><single-transition-property></dfn> = all | <IDENT>
280 </div>
282 <p>
283 A value of ''none'' means that no property will transition.
284 Otherwise, a list of properties to be transitioned, or the
285 keyword ''all'' which indicates that all properties are to be
286 transitioned, is given.
287 </p>
289 <p>
290 If one of the identifiers listed is not a recognized property
291 name or is not an animatable property, the implementation must
292 still start transitions on the animatable properties in the
293 list using the duration, delay, and timing function at their
294 respective indices in the lists for 'transition-duration',
295 'transition-delay', and 'transition-timing-function'. In other
296 words, unrecognized or non-animatable properties must be kept in
297 the list to preserve the matching of indices.
298 </p>
300 <p>
301 The keywords ''none'', ''inherit'', and ''initial'' are not
302 permitted as items within a list of more that one identifier;
303 any list that uses them is syntactically invalid.
304 In other words, the <IDENT> production in
305 <span><single-transition-property></span> matches any
306 identifier other than these three keywords.
307 </p>
309 <p>
310 For the keyword ''all'', or if one of the identifiers listed is a
311 shorthand property, implementations must start transitions for
312 any of its longhand sub-properties that are animatable (or, for
313 ''all'', all animatable properties), using the duration, delay,
314 and timing function at the index corresponding to the shorthand.
315 </p>
316 <p>
317 If a property is specified multiple times in the value of
318 'transition-property' (either on its own, via a shorthand that
319 contains it, or via the ''all'' value), then the transition that
320 starts uses the duration, delay, and timing function at the
321 index corresponding to the <em>last</em> item in the value of
322 'transition-property' that calls for animating that property.
323 </p>
324 <p class="note">
325 Note: The ''all'' value and 'all' shorthand
326 property work in similar ways, so the
327 ''all'' value is just like a shorthand that
328 covers all properties.
329 </p>
331 <!-- ======================================================================================================= -->
332 <h3 id="transition-duration-property"><a id="the-transition-duration-property-">
333 The 'transition-duration' Property
334 </a></h3>
335 <p>
336 The 'transition-duration' property defines the length of time that a transition takes.
337 </p>
338 <table class="propdef">
339 <tbody>
340 <tr>
341 <td>
342 <em>Name:</em>
343 </td>
344 <td>
345 <dfn id="transition-duration">transition-duration</dfn>
346 </td>
347 </tr>
348 <tr>
349 <td>
350 <em>Value:</em>
351 </td>
352 <td>
353 <span><time></span> [, <span><time></span>]*
354 </td>
355 </tr>
356 <tr>
357 <td>
358 <em>Initial:</em>
359 </td>
360 <td>
361 0s
362 </td>
363 </tr>
364 <tr>
365 <td>
366 <em>Applies to:</em>
367 </td>
368 <td>
369 all elements, :before and :after pseudo elements
370 </td>
371 </tr>
372 <tr>
373 <td>
374 <em>Inherited:</em>
375 </td>
376 <td>
377 no
378 </td>
379 </tr>
380 <tr>
381 <td>
382 <em>Animatable:</em>
383 </td>
384 <td>
385 no
386 </td>
387 </tr>
388 <tr>
389 <td>
390 <em>Percentages:</em>
391 </td>
392 <td>
393 N/A
394 </td>
395 </tr>
396 <tr>
397 <td>
398 <em>Media:</em>
399 </td>
400 <td>
401 interactive
402 </td>
403 </tr>
404 <tr>
405 <td>
406 <em>Computed value:</em>
407 </td>
408 <td>
409 Same as specified value.
410 </td>
411 </tr>
412 <tr>
413 <td>
414 <em>Canonical order:</em>
415 </td>
416 <td>
417 <abbr title="follows order of property value definition">per grammar</abbr>
418 </td>
419 </tr>
420 </tbody>
421 </table>
422 <p>
423 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.
424 </p>
426 <!-- =======================================================================================================
427 -->
429 <h3 id="transition-timing-function-property"><a id="transition-timing-function_tag">
430 The 'transition-timing-function' Property
431 </a></h3>
432 <p>
433 The 'transition-timing-function' property
434 describes how the intermediate values used during a transition will be
435 calculated. It allows for a transition to change speed over its
436 duration. These effects are commonly called <em>easing</em> functions.
437 In either case, a mathematical function that provides a smooth curve is
438 used.
439 </p>
440 <p>
441 Timing functions are either defined as a stepping function or
442 a <a
443 href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve#Cubic_B.C3.A9zier_curves">cubic
444 Bézier curve</a>.
445 The timing function takes as its input
446 the current elapsed percentage of the transition duration
447 and outputs the percentage of the way the transition is
448 from its start value to its end value.
449 How this output is used is defined by
450 the <a href="#animatable-types">interpolation rules</a>
451 for the value type.
452 </p>
453 <p>
454 A <a href="http://en.wikipedia.org/wiki/Step_function">stepping</a>
455 function is defined by a number that divides the domain of operation
456 into equally sized intervals. Each subsequent interval is a equal step
457 closer to the goal state. The function also specifies whether the
458 change in output percentage happens at the start or end of the
459 interval (in other words, if 0% on the input percentage is the point
460 of initial change).
461 </p>
462 <div class="figure">
463 <img src="step.png" alt="The step timing function splits
464 the function domain into a number of disjoint straight line
465 segments. steps(1, start) is a function whose
466 output value is 1 for all input values. steps(1, end) is a function whose
467 output value is 0 for all input values less than 1, and output
468 is 1 for the input value of 1. steps(3, start) is a function that
469 divides the input domain into three segments, each 1/3 in length,
470 and 1/3 above the previous segment, with the first segment starting
471 at 1/3. steps(3, end) is a function that
472 divides the input domain into three segments, each 1/3 in length,
473 and 1/3 above the previous segment, with the first segment starting
474 at 0.">
475 </div>
476 <p class="caption">
477 Step timing functions
478 </p>
479 <p>
480 A <a
481 href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve#Cubic_B.C3.A9zier_curves">cubic
482 Bézier curve</a> is defined by four control points, P<sub>0</sub>
483 through P<sub>3</sub> (see Figure 1). P<sub>0</sub> and P<sub>3</sub>
484 are always set to (0,0) and (1,1). The 'transition-timing-function' property is used
485 to specify the values for points P<sub>1</sub> and P<sub>2</sub>. These
486 can be set to preset values using the keywords listed below, or can be
487 set to specific values using the ''cubic-bezier'' function.
488 In the ''cubic-bezier'' function, P<sub>1</sub> and
489 P<sub>2</sub> are each specified by both an X and Y value.
490 </p>
491 <div class="figure">
492 <img src="TimingFunction.png" alt="The Bézier timing function is a
493 smooth curve from point P0 = (0,0) to point P3 = (1,1). The
494 length and orientation of the line segment P0-P1 determines
495 the tangent and the curvature of the curve at P0 and the
496 line segment P2-P3 does the same at P3.">
497 </div>
498 <p class="caption">
499 Bézier Timing Function Control Points
500 </p>
501 <table class="propdef">
502 <tbody>
503 <tr>
504 <td>
505 <em>Name:</em>
506 </td>
507 <td>
508 <dfn id="transition-timing-function">transition-timing-function</dfn>
509 </td>
510 </tr>
511 <tr>
512 <td>
513 <em>Value:</em>
514 </td>
515 <td>
516 <span><single-transition-timing-function></span> [ ',' <span><single-transition-timing-function></span> ]*
517 </td>
518 </tr>
519 <tr>
520 <td>
521 <em>Initial:</em>
522 </td>
523 <td>
524 ease
525 </td>
526 </tr>
527 <tr>
528 <td>
529 <em>Applies to:</em>
530 </td>
531 <td>
532 all elements, :before and :after pseudo elements
533 </td>
534 </tr>
535 <tr>
536 <td>
537 <em>Inherited:</em>
538 </td>
539 <td>
540 no
541 </td>
542 </tr>
543 <tr>
544 <td>
545 <em>Animatable:</em>
546 </td>
547 <td>
548 no
549 </td>
550 </tr>
551 <tr>
552 <td>
553 <em>Percentages:</em>
554 </td>
555 <td>
556 N/A
557 </td>
558 </tr>
559 <tr>
560 <td>
561 <em>Media:</em>
562 </td>
563 <td>
564 interactive
565 </td>
566 </tr>
567 <tr>
568 <td>
569 <em>Computed value:</em>
570 </td>
571 <td>
572 Same as specified value.
573 </td>
574 </tr>
575 <tr>
576 <td>
577 <em>Canonical order:</em>
578 </td>
579 <td>
580 <abbr title="follows order of property value definition">per grammar</abbr>
581 </td>
582 </tr>
583 </tbody>
584 </table>
585 <div class="prod">
586 <dfn id="single-transition-timing-function"><single-transition-timing-function></dfn> = ease | linear | ease-in | ease-out | ease-in-out | step-start | step-end | steps(<integer>[, [ start | end ] ]?) | cubic-bezier(<number>, <number>, <number>, <number>)
587 </div>
588 <p>
589 The timing functions have the following definitions.
590 </p>
591 <dl>
592 <dt>
593 ease
594 </dt>
595 <dd>
596 The ease function is equivalent to cubic-bezier(0.25, 0.1, 0.25, 1).
597 </dd>
598 <dt>
599 linear
600 </dt>
601 <dd>
602 The linear function is equivalent to cubic-bezier(0, 0, 1, 1).
603 </dd>
604 <dt>
605 ease-in
606 </dt>
607 <dd>
608 The ease-in function is equivalent to cubic-bezier(0.42, 0, 1, 1).
609 </dd>
610 <dt>
611 ease-out
612 </dt>
613 <dd>
614 The ease-out function is equivalent to cubic-bezier(0, 0, 0.58, 1).
615 </dd>
616 <dt>
617 ease-in-out
618 </dt>
619 <dd>
620 The ease-in-out function is equivalent to cubic-bezier(0.42, 0, 0.58, 1)
621 </dd>
622 <dt>
623 step-start
624 </dt>
625 <dd>
626 The step-start function is equivalent to steps(1, start).
627 </dd>
628 <dt>
629 step-end
630 </dt>
631 <dd>
632 The step-end function is equivalent to steps(1, end).
633 </dd>
634 <dt>
635 steps(<integer>[, [ start | end ] ]?)
636 </dt>
637 <dd>
638 Specifies a stepping function, described above, taking two
639 parameters. The first parameter specifies the number of intervals
640 in the function. It must be a positive integer (greater than 0).
641 The second parameter, which is optional, is
642 either the value ''start'' or ''end'', and specifies the point
643 at which the change of values occur within the interval.
644 If the second parameter is omitted, it is given the value 'end'.
645 </dd>
646 <dt>
647 cubic-bezier(<number>, <number>, <number>, <number>)
648 </dt>
649 <dd>
650 Specifies a <a
651 href="http://en.wikipedia.org/wiki/B%C3%A9zier_curve">cubic-bezier
652 curve</a>. The four values specify points P<sub>1</sub> and
653 P<sub>2</sub> of the curve as (x1, y1, x2, y2). Both x values must be
654 in the range [0, 1] or the definition is invalid. The y values can
655 exceed this range.
656 </dd>
657 </dl><!-- ======================================================================================================= -->
658 <h3 id="transition-delay-property"><a id="the-transition-delay-property-">
659 The 'transition-delay' Property
660 </a></h3>
661 <p>
662 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.
663 </p>
664 <p>
665 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.
666 </p>
667 <table class="propdef">
668 <tbody>
669 <tr>
670 <td>
671 <em>Name:</em>
672 </td>
673 <td>
674 <dfn id="transition-delay">transition-delay</dfn>
675 </td>
676 </tr>
677 <tr>
678 <td>
679 <em>Value:</em>
680 </td>
681 <td>
682 <span><time></span> [, <span><time></span>]*
683 </td>
684 </tr>
685 <tr>
686 <td>
687 <em>Initial:</em>
688 </td>
689 <td>
690 0s
691 </td>
692 </tr>
693 <tr>
694 <td>
695 <em>Applies to:</em>
696 </td>
697 <td>
698 all elements, :before and :after pseudo elements
699 </td>
700 </tr>
701 <tr>
702 <td>
703 <em>Inherited:</em>
704 </td>
705 <td>
706 no
707 </td>
708 </tr>
709 <tr>
710 <td>
711 <em>Animatable:</em>
712 </td>
713 <td>
714 no
715 </td>
716 </tr>
717 <tr>
718 <td>
719 <em>Percentages:</em>
720 </td>
721 <td>
722 N/A
723 </td>
724 </tr>
725 <tr>
726 <td>
727 <em>Media:</em>
728 </td>
729 <td>
730 interactive
731 </td>
732 </tr>
733 <tr>
734 <td>
735 <em>Computed value:</em>
736 </td>
737 <td>
738 Same as specified value.
739 </td>
740 </tr>
741 <tr>
742 <td>
743 <em>Canonical order:</em>
744 </td>
745 <td>
746 <abbr title="follows order of property value definition">per grammar</abbr>
747 </td>
748 </tr>
749 </tbody>
750 </table><!-- ======================================================================================================= -->
751 <h3 id="transition-shorthand-property"><a id="the-transition-shorthand-property-">
752 The 'transition' Shorthand Property
753 </a></h3>
754 <p>
755 The 'transition' shorthand property combines the four properties described above into a single property.
756 </p>
757 <table class="propdef">
758 <tbody>
759 <tr>
760 <td>
761 <em>Name:</em>
762 </td>
763 <td>
764 <dfn id="transition">transition</dfn>
765 </td>
766 </tr>
767 <tr>
768 <td>
769 <em>Value:</em>
770 </td>
771 <td>
772 <span><single-transition></span> [ ',' <span><single-transition></span> ]*
773 </td>
774 </tr>
775 <tr>
776 <td>
777 <em>Initial:</em>
778 </td>
779 <td>
780 see individual properties
781 </td>
782 </tr>
783 <tr>
784 <td>
785 <em>Applies to:</em>
786 </td>
787 <td>
788 all elements, :before and :after pseudo elements
789 </td>
790 </tr>
791 <tr>
792 <td>
793 <em>Inherited:</em>
794 </td>
795 <td>
796 no
797 </td>
798 </tr>
799 <tr>
800 <td>
801 <em>Animatable:</em>
802 </td>
803 <td>
804 no
805 </td>
806 </tr>
807 <tr>
808 <td>
809 <em>Percentages:</em>
810 </td>
811 <td>
812 N/A
813 </td>
814 </tr>
815 <tr>
816 <td>
817 <em>Media:</em>
818 </td>
819 <td>
820 interactive
821 </td>
822 </tr>
823 <tr>
824 <td>
825 <em>Computed value:</em>
826 </td>
827 <td>
828 see individual properties
829 </td>
830 </tr>
831 <tr>
832 <td>
833 <em>Canonical order:</em>
834 </td>
835 <td>
836 <abbr title="follows order of property value definition">per grammar</abbr>
837 </td>
838 </tr>
839 </tbody>
840 </table>
842 <div class="prod">
843 <dfn id="single-transition"><single-transition></dfn> = [ none | <span><single-transition-property></span> ] || <span><time></span> || <span><single-transition-timing-function></span> || <span><time></span>
844 </div>
846 <p>
847 Note that order is important within the items in this property:
848 the first value that can be parsed as a time is assigned to the
849 transition-duration,
850 and the second value that can be parsed as a time is assigned to
851 transition-delay.
852 </p>
854 <p>
855 If there is more than one <span><single-transition></span> in the shorthand,
856 and any of the transitions has
857 ''none'' as the <span><single-transition-property></span>,
858 then the declaration is invalid.
859 </p>
861 <h2 id="starting">
862 Starting of transitions
863 </h2>
865 <p>
866 When the computed value of an animatable property changes,
867 implementations must decide what transitions to start based on
868 the values of the 'transition-property', 'transition-duration',
869 'transition-timing-function', and 'transition-delay' properties
870 at the time the animatable property would first have its new
871 computed value.
872 This means that when one of these 'transition-*' properties
873 changes at the same time as
874 a property whose change might transition,
875 it is the <em>new</em> values of the 'transition-*' properties
876 that control the transition.
877 </p>
878 <div class="example" id="manual-reversing-example">
879 <p style="display:none">
880 Example(s):
881 </p>
882 <p>This provides a way for authors to specify different values
883 of the 'transition-*' properties for the “forward”
884 and “reverse” transitions (but see <a
885 href="#reversing">below</a> for special reversing behavior when
886 an <em>incomplete</em> transition is interrupted). Authors can
887 specify the value of 'transition-duration',
888 'transition-timing-function', or 'transition-delay' in the same
889 rule where they specify the value that triggers the transition,
890 or can change these properties at the same time as they change
891 the property that triggers the transition. Since it's the new
892 values of these 'transition-*' properties that affect the
893 transition, these values will be used for the transitions
894 <em>to</em> the associated transitioning values. For example:
895 </p>
896 <pre>li {
897 transition: background-color linear 1s;
898 background: blue;
899 }
900 li:hover {
901 background-color: green;
902 transition-duration: 2s; /* applies to the transition *to* the :hover state */
903 }</pre>
904 <p>
905 When a list item with these style rules enters the :hover
906 state, the computed 'transition-duration' at the time that
907 'background-color' would have its new value (''green'') is ''2s'',
908 so the transition from 'blue' to 'green' takes 2 seconds.
909 However, when the list item leaves the :hover state, the
910 transition from ''green'' to ''blue'' takes 1 second.
911 </p>
912 </div>
914 <p>
915 Various things can cause the computed style of an element to change,
916 or for an element to start or stop having computed style.
917 (For the purposes of this specification,
918 an element has computed style when it is in the document tree,
919 and does not have computed style when it is not in the document tree.)
920 These include
921 insertion and removal of elements from the document tree
922 (which both changes whether those elements have computed styles and
923 can change the styles of other elements through selector matching),
924 changes to the document tree that cause
925 changes to which selectors match elements,
926 changes to style sheets or style attributes,
927 and other things.
928 This specification does not define when computed styles are updated.
929 However,
930 when an implementation updates the computed style for an element
931 to reflect one of these changes,
932 it must update the computed style for all elements to reflect all
933 of these changes at the same time
934 (or at least it must be undetectable that it was done at a
935 different time).
936 This processing of a set of simultaneous style changes is called a
937 <dfn>style change event</dfn>.
938 (Implementations typically have a <span>style change event</span> to
939 correspond with their desired screen refresh rate,
940 and when up-to-date computed style is needed
941 for a script API that depends on it.)
942 </p>
944 <p>
945 Since this specification does not define
946 when a <span>style change event</span> occurs,
947 and thus what changes to computed values are considered simultaneous,
948 authors should be aware that changing any of the transition
949 properties a small amount of time after making a change that
950 might transition can result in behavior that varies between
951 implementations, since the changes might be considered
952 simultaneous in some implementations but not others.
953 </p>
955 <p>
956 When a <span>style change event</span> occurs,
957 implementations must start transitions based on
958 the computed styles that changed in that event.
959 If an element does not have a computed style
960 either before or after the style change event,
961 then transitions are not started for that element
962 in that style change event.
963 Otherwise,
964 define the <dfn>before-change style</dfn> as
965 the computed style for the element as of
966 the previous <span>style change event</span>,
967 except with any styles derived from declarative
968 animations such as CSS Transitions, CSS Animations
969 ([[CSS3-ANIMATIONS]]),
970 and SMIL Animations ([[SMIL-ANIMATION]], [[SVG11]])
971 updated to the current time.
972 Likewise, define the <dfn>after-change style</dfn> as
973 the computed style for the element based on the information
974 known at the start of that <span>style change event</span>,
975 in other words,
976 excluding any changes resulting from CSS Transitions
977 that start during that <span>style change event</span>.
978 </p>
980 <p class="issue">
981 This wording needs to handle already-running transitions better!
982 </p>
984 <div class="note">
985 <p>
986 Note that this definition of the <span>after-change style</span>
987 means that a single change
988 can start a transition on the same property
989 on both an ancestor element and its descendant element.
990 This can happen when a property change is inherited
991 from one element with 'transition-*' properties
992 that say to animate the changing property
993 to another element with 'transition-*' properties
994 that also say to animate the changing property.
995 </p>
997 <p>
998 When this happens, both transitions will run,
999 and the transition on the descendant will override
1000 the transition on the ancestor
1001 because of the normal
1002 CSS cascading and inheritance rules ([[CSS3CASCADE]]).
1003 </p>
1005 <p>
1006 If the transition on the descendant completes before
1007 the transition on the ancestor,
1008 the descendant will then resume inheriting
1009 the (still transitioning) value from its parent.
1010 This effect is likely not a desirable effect,
1011 but it is essentially doing what the author asked for.
1012 </p>
1013 </div>
1015 <p>
1016 For each element with a <span>before-change style</span> and
1017 an <span>after-change style</span>,
1018 and each property (other than shorthands) for which
1019 the <span>before-change style</span> is different from
1020 the <span>after-change style</span>,
1021 implementations must
1022 start transitions based on the relevant item (see <a
1023 href="#transition-property">the definition of
1024 'transition-property'</a>) in the computed value of
1025 'transition-property'.
1026 Corresponding to this item there is
1027 a <span>matching transition duration</span>,
1028 a <span>matching transition delay</span>, and
1029 a <span>matching transition timing function</span>
1030 in the computed values of
1031 'transition-duration', 'transition-delay', and 'transition-timing-function'
1032 (see <a href="#list-matching">the rules on matching lists</a>).
1033 Define the <dfn>combined duration</dfn> of the transition
1034 as the sum of max(matching transition duration, ''0s'') and
1035 the matching transition-delay.
1036 When the combined duration is greater than ''0s'',
1037 then a transition starts based on the values of the
1038 matching transition duration, the matching transition delay,
1039 and the matching transition-timing-function;
1040 in other cases transitions do not occur.
1041 The <dfn>start time</dfn> of this transition is defined as
1042 the time of the <span>style change event</span> plus
1043 the matching transition delay.
1044 The <dfn>end time</dfn> of this transition is defined as
1045 the <span>start time</span> plus the matching transition duration.
1046 </p>
1048 <p>
1049 Once the transition of a property has started, it must continue
1050 running based on the original timing function, duration, and
1051 delay, even if the 'transition-timing-function',
1052 'transition-duration', or 'transition-delay' property changes
1053 before the transition is complete. However, if the
1054 'transition-property' property changes such that the transition
1055 would not have started, the transition must stop (and the
1056 property must immediately change to its final value).
1057 </p>
1059 <p>
1060 Implementations must not start a transition when the computed
1061 value of a property changes as a result of declarative animation
1062 (as opposed to scripted animation).
1063 </p>
1065 <p>
1066 Implementations also must not start a transition when the
1067 computed value changes because it is inherited (directly or
1068 indirectly) from another element that is transitioning the same
1069 property.
1070 </p>
1072 <h2 id="application">
1073 Application of transitions
1074 </h2>
1076 <p>
1077 When a property on an element is undergoing a transition
1078 (that is, when or after the transition has started and before the
1079 <span>end time</span> of the transition)
1080 the transition adds a style to the CSS cascade
1081 at the level defined for CSS Transitions in [[CSS3CASCADE]].
1082 </p>
1084 <p class="note">
1085 Note that this means that computed values
1086 resulting from CSS transitions
1087 can inherit to descendants just like
1088 any other computed values.
1089 In the normal case, this means that
1090 a transition of an inherited property
1091 applies to descendant elements
1092 just as an author would expect.
1093 </p>
1095 <p>
1096 Implementations must add this value to the cascade
1097 if and only if
1098 that property is not currently
1099 undergoing a CSS Animation ([[CSS3-ANIMATIONS]]) on the same element.
1100 </p>
1102 <p class="note">
1103 Note that this behavior of transitions not applying to the cascade
1104 when an animation on the same element and property is running
1105 does not affect whether the transition has started or ended.
1106 APIs that detect whether transitions are running
1107 (such as <a href="#transition-events">transition events</a>)
1108 still report that a transition is running.
1109 </p>
1111 <p>
1112 If the current time is at or before the
1113 <span>start time</span> of the transition
1114 (that is, during the delay phase of the transition),
1115 this value is a specified style that will compute
1116 to the <span>before-change style</span> in the
1117 <span>style change event</span> in which the transition was started.
1118 </p>
1120 <p>
1121 If the current time is after the
1122 <span>start time</span> of the transition
1123 (that is, during the duration phase of the transition),
1124 this value is a specified style that will compute
1125 to the <a href="#animatable-types">result of interpolating the property</a>
1126 using the <span>before-change style</span> for the property as
1127 <i>V</i><sub>start</sub>,
1128 using the <span>after-change style</span> for the property as
1129 <i>V</i><sub>end</sub>,
1130 and using (current time - start time) / (end time - start time)
1131 as the input to the timing function.
1132 (The <span>before-change style</span> and <span>after-change style</span>
1133 <span>style change event</span> in which the transition was started.)
1134 </p>
1136 <h2 id="reversing">
1137 Automatically reversing interrupted transitions
1138 </h2>
1139 <p>
1140 A common type of transition effect is when a running transition is
1141 interrupted and the property is reset to its original value. An
1142 example is a hover effect on an element, where the pointer enters and
1143 exits the element before the effect has completed. If the outgoing and
1144 incoming transitions are executed using their specified durations and
1145 timing functions, the resulting effect can be distractingly
1146 asymmetric. Instead, the expected behavior is that the new transition
1147 should be the reverse of what has already executed.
1148 </p>
1150 <p>
1151 If a running transition with duration T, executing so far for duration TE,
1152 from state A, to state B, is interrupted by
1153 a property change that would start a new transition back to state A, and
1154 all the transition attributes are the same (duration, delay and timing function),
1155 then the new transition must reverse the effect. The new transition must:
1156 </p>
1158 <ol>
1159 <li>
1160 Use the B and A states as its "from" and "to" states respectively. It
1161 does not use the current value as its from state, due to the rules below.
1162 </li>
1163 <li>
1164 Execute with the same duration T, but starting as if the transition had
1165 already begun, without any transition delay, at the moment which would
1166 cause the new transition to finish in TE from the moment of interruption. In other
1167 words, the new transition will execute as if it started T-TE in the past.
1168 </li>
1169 <li>
1170 Use a timing function that is the portion of the curve traversed up
1171 to the moment of interruption, followed in the opposite direction (towards
1172 the starting point). This will make the transition appear as if it
1173 is playing backwards.
1174 </li>
1175 <li>
1176 Ignore any transition delay.
1177 </li>
1178 </ol>
1180 <p>
1181 For example, suppose there is a transition with a duration of two
1182 seconds. If this transition is interrupted after 0.5 seconds and the
1183 property value assigned to the original value, then the new transition
1184 effect will be the reverse of the original, as if it had begun
1185 1.5 seconds in the past.
1186 </p>
1188 <p>
1189 Note that by using the defined from and to states for the reversing
1190 transition, it is also possible that it may reverse again, if
1191 interrupted; for example, if the transition reversing to state A was
1192 again interrupted by a property change to state B.
1193 </p>
1195 <p class="issue">Issue:
1196 This introduces the concept of reversing a timing function,
1197 which the spec has otherwise resisted doing, and also introduces
1198 a discontinuity between transitions that have
1199 almost completed (which get automatically reversed and thus have
1200 their timing function reversed) and transitions that have fully
1201 completed (where the reversal doesn't lead to the timing
1202 function being reversed). An alternative proposal that avoids
1203 this is to follow the normal timing function algorithm, except
1204 multiply the duration (and also shorten any negative delay) by
1205 the (output) value of the transition timing function of the
1206 incomplete transition at the time it was interrupted, and, to
1207 account for multiple reverses in sequence, to divide by the
1208 shortening applied to the transition being interrupted. For
1209 more details see this thread:
1210 <a href="http://lists.w3.org/Archives/Public/www-style/2009Nov/thread.html#msg302">November 2009 part</a>,
1211 <a href="http://lists.w3.org/Archives/Public/www-style/2009Dec/thread.html#msg319">December 2009 part</a>,
1212 <a href="http://lists.w3.org/Archives/Public/www-style/2010Jan/thread.html#msg136">January 2010 part</a>.
1213 Also see:
1214 <a href="http://lists.w3.org/Archives/Public/public-fx/2012AprJun/0107.html">minutes 2012-05-09</a> (and <a href="http://www.w3.org/Graphics/fx/track/actions/77">action</a>),
1215 <a href="http://lists.w3.org/Archives/Public/www-style/2012Nov/0262.html">minutes 2012-10-30</a>,
1216 <a href="transition-reversing-demo">reversing demo</a>.
1217 Working Group resolution from 2013-06-07 needs to be edited.
1218 </p>
1220 <h2 id="transition-events"><a id="transition-events-">
1221 Transition Events
1222 </a></h2>
1223 <p>
1224 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>.
1225 An event is fired for each property that undergoes a transition.
1226 This allows a content developer to perform actions that synchronize
1227 with the completion of a transition.
1228 </p>
1229 <p>
1230 Each event provides the name of the property the transition is
1231 associated with as well as the duration of the transition.
1232 </p>
1233 <dl>
1234 <dt>
1235 <b>Interface <dfn id="Events-TransitionEvent">TransitionEvent</dfn></b>
1236 </dt>
1237 <dd>
1238 <p>
1239 The <code>TransitionEvent</code> interface provides specific contextual information associated with transitions.
1240 </p>
1241 <dl>
1242 <dt>
1243 <b>IDL Definition</b>
1244 </dt>
1245 <dd>
1246 <div class='idl-code'>
1247 <pre>
1248 <span id="TransitionEvent">[Constructor(DOMString <var title="">type</var>, optional <i>TransitionEventInit</i> <var title="">transitionEventInitDict</var>)]
1249 interface TransitionEvent</span> : Event {
1250 readonly attribute DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a>;
1251 readonly attribute float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a>;
1252 readonly attribute DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a>;
1253 };
1255 dictionary <dfn id="TransitionEventInit">TransitionEventInit</dfn> : <a class="external" href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#eventinit">EventInit</a> {
1256 DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a> = "";
1257 float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a> = 0.0;
1258 DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a> = "";
1259 }
1260 </pre>
1261 </div>
1262 </dd>
1263 <dt>
1264 <b>Attributes</b>
1265 </dt>
1266 <dd>
1267 <dl>
1268 <dt>
1269 <code class='attribute-name'><dfn title="TransitionEvent::propertyName" id="Events-TransitionEvent-propertyName">propertyName</dfn></code> of type <code>DOMString</code>, readonly
1270 </dt>
1271 <dd>
1272 The name of the CSS property associated with the transition.
1273 </dd>
1274 </dl>
1275 <dl>
1276 <dt>
1277 <code class='attribute-name'><dfn title="TransitionEvent::elapsedTime" id="Events-TransitionEvent-elapsedTime">elapsedTime</dfn></code> of type <code>float</code>, readonly
1278 </dt>
1279 <dd>
1280 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>.
1281 </dd>
1282 </dl>
1283 <dl>
1284 <dt>
1285 <code class='attribute-name'><dfn title="TransitionEvent::pseudoElement" id="Events-TransitionEvent-pseudoElement">pseudoElement</dfn></code> of type <code>DOMString</code>, readonly
1286 </dt>
1287 <dd>
1288 The name (beginning with two colons) of the CSS
1289 pseudo-element on which the transition occured (in
1290 which case the target of the event is that
1291 pseudo-element's corresponding element), or the empty
1292 string if the transition occurred on an element (which
1293 means the target of the event is that element).
1294 </dd>
1295 </dl>
1296 </dd>
1297 </dl>
1298 <p>
1299 <code id="TransitionEvent-constructor">TransitionEvent(type, transitionEventInitDict)</code>
1300 is an <a class="external" href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#constructing-events">event constructor</a>.
1301 </p>
1302 </dd>
1303 </dl>
1304 <p>
1305 There is one type of transition event available.
1306 </p>
1307 <dl>
1308 <dt>
1309 <b><dfn>transitionend</dfn></b>
1310 </dt>
1311 <dd>
1312 The <code>transitionend</code> event occurs at the completion of the transition. In the
1313 case where a transition is removed before completion, such as if the
1314 transition-property is removed, then the event will not fire.
1315 <ul>
1316 <li>Bubbles: Yes
1317 </li>
1318 <li>Cancelable: Yes
1319 </li>
1320 <li>Context Info: propertyName, elapsedTime, pseudoElement
1321 </li>
1322 </ul>
1323 </dd>
1324 </dl>
1326 <h2 id="animatable-types"><a id="animation-of-property-types-">
1327 Animation of property types
1328 </a></h2>
1330 <p>
1331 When interpolating between two values,
1332 <i>V</i><sub>start</sub> and <i>V</i><sub>end</sub>,
1333 interpolation is done using the output <i>p</i> of the timing function,
1334 which gives the portion of the value space
1335 that the interpolation has crossed.
1336 Thus the result of the interpolation is
1337 <i>V</i><sub>res</sub> =
1338 (1 - <i>p</i>) ⋅ <i>V</i><sub>start</sub> +
1339 <i>p</i> ⋅ <i>V</i><sub>end</sub>.
1340 </p>
1342 <p>
1343 However, if this value (<i>V</i><sub>res</sub>)
1344 is outside the allowed range of values for the property,
1345 then it is clamped to that range.
1346 This can occur if <i>p</i> is outside of the range 0 to 1,
1347 which can occur if a timing function is specified
1348 with a <i>y1</i> or <i>y2</i> that is outside the range 0 to 1.
1349 </p>
1351 <p>
1352 The following describes how each property type undergoes transition or
1353 animation.
1354 </p>
1356 <ul>
1357 <li id="animtype-color">
1358 <strong>color</strong>: interpolated via red, green, blue and alpha
1359 components (treating each as a number, see below).
1360 The interpolation is done between premultiplied colors
1361 (that is, colors for which the red, green, and blue components
1362 specified have been multiplied by the alpha).
1363 </li>
1364 <li id="animtype-length">
1365 <strong>length</strong>: interpolated as real numbers.
1366 </li>
1367 <li id="animtype-percentage">
1368 <strong>percentage</strong>: interpolated as real numbers.
1369 </li>
1370 <li id="animtype-lpcalc">
1371 <strong>length, percentage, or calc</strong>: when both values
1372 are lengths, interpolated as lengths; when both values are
1373 percentages, interpolated as percentages; otherwise, both
1374 values are converted into a ''calc()'' function that is the
1375 sum of a length and a percentage (each possibly zero), and
1376 these ''calc()'' functions have each half interpolated as real
1377 numbers.
1378 </li>
1379 <li id="animtype-integer">
1380 <strong>integer</strong>: interpolated via discrete steps (whole
1381 numbers). The interpolation happens in real number space and is
1382 converted to an integer by rounding to the nearest integer, with
1383 values halfway between a pair of integers rounded towards
1384 positive infinity.
1385 </li>
1386 <li id="animtype-font-weight">
1387 <strong>font weight</strong>: interpolated via discrete steps
1388 (multiples of 100). The interpolation happens in real number
1389 space and is converted to an integer by rounding to the
1390 nearest multiple of 100, with values halfway between multiples
1391 of 100 rounded towards positive infinity.
1392 </li>
1393 <li id="animtype-number">
1394 <strong>number</strong>: interpolated as real (floating point)
1395 numbers.
1396 </li>
1397 <li id="animtype-rect">
1398 <strong>rectangle</strong>: interpolated via the x, y,
1399 width and height components (treating each as a number).
1400 </li>
1401 <li id="animtype-visibility">
1402 <strong>visibility</strong>: if one of the values is
1403 ''visible'', interpolated as a discrete step where values of the
1404 timing function between 0 and 1 map to ''visible'' and other
1405 values of the timing function (which occur only at the
1406 start/end of the transition or as a result of ''cubic-bezier()''
1407 functions with Y values outside of [0, 1]) map to the closer
1408 endpoint; if neither value is ''visible'' then not interpolable.
1409 </li>
1410 <li id="animtype-shadow-list">
1411 <strong>shadow list</strong>: Each shadow in the list is
1412 interpolated via the
1413 color (as <a href="#animtype-color">color</a>) component,
1414 and x, y, blur, and (when appropriate) spread
1415 (as <a href="#animtype-length">length</a>) components.
1416 For each shadow, if one input shadow is ''inset'' and the other
1417 is not, then the result for that shadow matches the inputs;
1418 otherwise the entire list is not interpolable.
1419 If the lists of shadows have different lengths,
1420 then the shorter list is padded at the end
1421 with shadows whose color is ''transparent'',
1422 all lengths are ''0'',
1423 and whose ''inset'' (or not) matches the longer list.
1424 </li>
1425 <li id="animtype-gradient">
1426 <strong>gradient</strong>: interpolated via the
1427 positions and colors of each stop. They must have the same type
1428 (radial or linear) and same number of stops in order to be animated.
1429 <span class="note">Note: [[CSS3-IMAGES]] may extend this
1430 definition.</span>
1431 </li>
1432 <li id="animtype-paintserver">
1433 <strong>paint server</strong> (SVG): interpolation is only supported
1434 between: gradient to gradient and color to color. They then
1435 work as above.
1436 </li>
1437 <li id="animtype-simple-list">
1438 <strong>simple list</strong> of other types:
1439 If the lists have the same number of items,
1440 and each pair of values can be interpolated,
1441 each item in the list is interpolated using
1442 the rules given for those types.
1443 Otherwise the values are not interpolable.
1444 </li>
1445 <li id="animtype-repeatable-list">
1446 <strong>repeatable list</strong> of other types:
1447 The result list has a length that is the least common multiple
1448 of the lengths of the input lists.
1449 Each item in the result is the interpolation of the value
1450 from each input list repeated to the length of the result list.
1451 If a pair of values cannot be interpolated, then the lists
1452 are not interpolable.
1453 <span class="note">
1454 The repeatable list concept ensures that a list that is
1455 conceptually repeated to a certain length (as
1456 'background-origin' is repeated to the length of the
1457 'background-image' list) or repeated infinitely will
1458 smoothly transition between any values, and so that the
1459 computed value will properly represent the result (and
1460 potentially be inherited correctly).
1461 </span>
1462 </li>
1463 </ul>
1465 <p>Future specifications may define additional types that can
1466 be animated.</p>
1468 <p>See the definition of 'transition-property' for how animation
1469 of shorthand properties and the ''all'' value is applied to any
1470 properties (in the shorthand) that can be animated.</p>
1472 <h2 id="animatable-properties"><a id="animatable-properties-">
1473 Animatable properties
1474 </a></h2>
1476 <!--
1477 As resolved in
1478 http://lists.w3.org/Archives/Public/www-style/2011Sep/0497.html
1479 -->
1481 <p>The definition of each CSS property defines
1482 when the values of that property can be interpolated
1483 by referring to the definitions of property types
1484 in the <a href="#animatable-types">previous section</a>.
1485 Values are animatable when
1486 both the from and the to values of the property have the type described.
1487 (When a composite type such as "length, percentage, or calc" is listed,
1488 this means that both values must fit into that composite type.)
1489 When multiple types are listed in the form "either A or B",
1490 both values must be of the same type to be interpolable.</p>
1492 <p>For properties that exist at the time this specification was
1493 developed, this specification defines whether and how they are
1494 animated. However, future CSS specifications may define
1495 additional properties, additional values for existing properties,
1496 or additional animation behavior of existing values. In order to
1497 describe new animation behaviors and to have the definition of
1498 animation behavior in a more appropriate location, future CSS
1499 specifications should include an "Animatable:" line in the summary
1500 of the property's definition (in addition to the other lines
1501 described in [[CSS21]], <a
1502 href="http://www.w3.org/TR/CSS21/about.html#property-defs">section
1503 1.4.2</a>). This line should say "no" to indicate that a property
1504 cannot be animated or should reference an animation behavior
1505 (which may be one of the behaviors in the <a
1506 href="#animation-of-property-types-">Animation of property
1507 types</a> section above, or may be a new behavior) to define how
1508 the property animates. Such definitions override those given in
1509 this specification.</p>
1511 <h3 id="animatable-css"><a id="properties-from-css-">
1512 Properties from CSS
1513 </a></h3>
1515 <p>
1516 The following definitions define the animation behavior for
1517 properties in CSS Level 2 Revision 1 ([[CSS21]]) and in Level 3 of
1518 the CSS Color Module ([[CSS3COLOR]]).
1519 </p>
1521 <table class="animatable-properties">
1522 <tr>
1523 <th>Property Name</th>
1524 <th>Type</th>
1525 </tr>
1526 <tr>
1527 <td>background-color</td><td>as <a href="#animtype-color">color</a></tr>
1528 <tr>
1529 <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>
1530 </tr>
1531 <tr>
1532 <td>border-bottom-color</td><td>as <a href="#animtype-color">color</a></td>
1533 </tr>
1534 <tr>
1535 <td>border-bottom-width</td><td>as <a href="#animtype-length">length</a></td>
1536 </tr>
1537 <tr>
1538 <td>border-left-color</td><td>as <a href="#animtype-color">color</a></td>
1539 </tr>
1540 <tr>
1541 <td>border-left-width</td><td>as <a href="#animtype-length">length</a></td>
1542 </tr>
1543 <tr>
1544 <td>border-right-color</td><td>as <a href="#animtype-color">color</a></td>
1545 </tr>
1546 <tr>
1547 <td>border-right-width</td><td>as <a href="#animtype-length">length</a></td>
1548 </tr>
1549 <tr>
1550 <td>border-spacing</td><td>as <a href="#animtype-simple-list">simple list</a> of <a href="#animtype-length">length</a></td>
1551 </tr>
1552 <tr>
1553 <td>border-top-color</td><td>as <a href="#animtype-color">color</a></td>
1554 </tr>
1555 <tr>
1556 <td>border-top-width</td><td>as <a href="#animtype-length">length</a></td>
1557 </tr>
1558 <tr>
1559 <td>bottom</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1560 </tr>
1561 <tr>
1562 <td>clip</td><td>as <a href="#animtype-rect">rectangle</a></td>
1563 </tr>
1564 <tr>
1565 <td>color</td><td>as <a href="#animtype-color">color</a></td>
1566 </tr>
1567 <tr>
1568 <td>font-size</td><td>as <a href="#animtype-length">length</a></td>
1569 </tr>
1570 <tr>
1571 <td>font-weight</td><td>as <a href="#animtype-font-weight">font weight</a></td>
1572 </tr>
1573 <tr>
1574 <td>height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1575 </tr>
1576 <tr>
1577 <td>left</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1578 </tr>
1579 <tr>
1580 <td>letter-spacing</td><td>as <a href="#animtype-length">length</a></td>
1581 </tr>
1582 <tr>
1583 <td>line-height</td><td>as either <a href="#animtype-number">number</a> or <a href="#animtype-length">length</a></td>
1584 </tr>
1585 <tr>
1586 <td>margin-bottom</td><td>as <a href="#animtype-length">length</a></td>
1587 </tr>
1588 <tr>
1589 <td>margin-left</td><td>as <a href="#animtype-length">length</a></td>
1590 </tr>
1591 <tr>
1592 <td>margin-right</td><td>as <a href="#animtype-length">length</a></td>
1593 </tr>
1594 <tr>
1595 <td>margin-top</td><td>as <a href="#animtype-length">length</a></td>
1596 </tr>
1597 <tr>
1598 <td>max-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1599 </tr>
1600 <tr>
1601 <td>max-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1602 </tr>
1603 <tr>
1604 <td>min-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1605 </tr>
1606 <tr>
1607 <td>min-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1608 </tr>
1609 <tr>
1610 <td>opacity</td><td>as <a href="#animtype-number">number</a></td>
1611 </tr>
1612 <tr>
1613 <td>outline-color</td><td>as <a href="#animtype-color">color</a></td>
1614 </tr>
1615 <tr>
1616 <td>outline-width</td><td>as <a href="#animtype-length">length</a></td>
1617 </tr>
1618 <tr>
1619 <td>padding-bottom</td><td>as <a href="#animtype-length">length</a></td>
1620 </tr>
1621 <tr>
1622 <td>padding-left</td><td>as <a href="#animtype-length">length</a></td>
1623 </tr>
1624 <tr>
1625 <td>padding-right</td><td>as <a href="#animtype-length">length</a></td>
1626 </tr>
1627 <tr>
1628 <td>padding-top</td><td>as <a href="#animtype-length">length</a></td>
1629 </tr>
1630 <tr>
1631 <td>right</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1632 </tr>
1633 <tr>
1634 <td>text-indent</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1635 </tr>
1636 <tr>
1637 <td>text-shadow</td><td>as <a href="#animtype-shadow-list">shadow list</a></td>
1638 </tr>
1639 <tr>
1640 <td>top</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1641 </tr>
1642 <tr>
1643 <td>vertical-align</td><td>as <a href="#animtype-length">length</a></td>
1644 </tr>
1645 <tr>
1646 <td>visibility</td><td>as <a href="#animtype-visibility">visibility</a></td>
1647 </tr>
1648 <tr>
1649 <td>width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1650 </tr>
1651 <tr>
1652 <td>word-spacing</td><td>as <a href="#animtype-length">length</a></td>
1653 </tr>
1654 <tr>
1655 <td>z-index</td><td>as <a href="#animtype-integer">integer</a></td>
1656 </tr>
1657 </table>
1659 <h3 id="animatable-svg"><a id="properties-from-svg-">
1660 Properties from SVG
1661 </a></h3>
1663 <p>
1664 All properties defined as animatable in the SVG specification, provided
1665 they are one of the property types listed above.
1666 </p>
1668 <!-- <table>
1669 <tr>
1670 <th>Property Name</th><th>Type</th>
1671 </tr>
1672 <tr>
1673 <td>stop-color</td><td>as <a href="#animtype-color">color</a></td>
1674 </tr>
1675 <tr>
1676 <td>stop-opacity</td><td>as <a href="#animtype-number">number</a></td>
1677 </tr>
1678 <tr>
1679 <td>fill</td><td>as <a href="#animtype-paintserver">paint server</a></td>
1680 </tr>
1681 <tr>
1682 <td>fill-opacity</td><td>as <a href="#animtype-number">number</a></td>
1683 </tr>
1684 <tr>
1685 <td>stroke</td><td>as <a href="#animtype-paintserver">paint server</a></td>
1686 </tr>
1687 <tr>
1688 <td>stroke-dasharray</td><td>as <a href="#animtype-repeatable-list">repeatable list</a> of <a href="#animtype-number">number</a></td>
1689 </tr>
1690 <tr>
1691 <td>stroke-dashoffset</td><td>as <a href="#animtype-number">number</a></td>
1692 </tr>
1693 <tr>
1694 <td>stroke-miterlimit</td><td>as <a href="#animtype-number">number</a></td>
1695 </tr>
1696 <tr>
1697 <td>stroke-opacity</td><td>as <a href="#animtype-number">number</a></td>
1698 </tr>
1699 <tr>
1700 <td>stroke-width</td><td>as <a href="#animtype-number">number</a></td>
1701 </tr>
1702 <tr>
1703 <td>viewport-fill</td><td>as <a href="#animtype-color">color</a></td>
1704 </tr>
1705 <tr>
1706 <td>viewport-fill-opacity</td><td>as <a href="#animtype-color">color</a></td>
1707 </tr>
1708 </table> -->
1710 <h2 id="changes">Changes since Working Draft of 12 February 2013</h2>
1712 <p>The following are the substantive changes made since the
1713 <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20130212/">Working Draft
1714 dated 12 February 2013</a>:</p>
1716 <ul>
1717 <li>Fixed missed substitution (<span>TransitionEventInit</span> rather than AnimationEventInit) when copying event IDL from css3-animations.
1718 <li>Make naming of event constructor dictionary parameters more consistent with DOM-Level-3-Events.
1719 <li>Make the behavior of simultaneous changes of 'transition-*' properties and transitionable properties even clearer.
1720 <li>Computed Value line for shorthands should say "see individual properties".
1721 <li>Define initial values of event properties, using initializers in <span>TransitionEventInit</span>.
1722 <li>Define the model for starting of transitions and their interaction with other animations more precisely:
1723 <ul>
1724 <li>Define the <span>before-change style</span> and <span>after-change style</span> used for the style comparison, using the new concept of a <span>style change event</span>.
1725 <li>Define that a CSS transition for a property does not affect computed style when a CSS Animation for the same property is running, but that the transition is still running in terms of APIs.
1726 <li>Add a note pointing out that the above definitions imply that transitions can start simultaneously, from the same change, on ancestors and descendants.
1727 <li>Define that CSS transitions participate in CSS's cascading and inheritance model
1728 </ul>
1729 </ul>
1731 <p>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>.
1733 <p>For changes in previous working drafts, see
1734 <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20130212/ChangeLog">the ChangeLog</a>, and the above version control logs.</p>
1736 <h2 id="acknowledgments">Acknowledgments</h2>
1738 <p>Thanks especially to the feedback from
1739 Tab Atkins,
1740 Carine Bournez,
1741 Aryeh Gregor,
1742 Vincent Hardy,
1743 Anne van Kesteren,
1744 Cameron McCormack,
1745 Alex Mogilevsky,
1746 and all the rest of the
1747 <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.</p>
1749 <h2 id="references">References</h2>
1751 <h3 class="no-num" id="normative-references">Normative references</h3>
1752 <!--normative-->
1754 <h3 class="no-num" id="other-references">Other references</h3>
1755 <!--informative-->
1759 <h2 class="no-num" id="property-index">Property index</h2>
1760 <!-- properties -->
1764 <h2 class="no-num" id="index">Index</h2>
1765 <!--index-->
1767 </body>
1768 </html>
1769 <!-- Keep this comment at the end of the file
1770 Local variables:
1771 mode: sgml
1772 sgml-default-doctype-name:"html"
1773 sgml-minimize-attributes:t
1774 End:
1775 -->
