[css-transitions][css-animations] Properties that cannot be interpolated transition at the midpoint of the timing function.

This is as resolved in:
https://lists.w3.org/Archives/Public/www-style/2012Nov/0261.html
https://lists.w3.org/Archives/Public/www-style/2014Oct/0290.html

Author: dbaron

css-animations/Overview.bs

@@ -308,6 +308,13 @@ Keyframes</h2>
 		{T}{O}                         {return TO_SYM;}
 	</pre>
 
+	<p class="issue">
+		This specification needs to define
+		how the value is determined from the keyframes,
+		like the section on
+		<a href="http://dev.w3.org/csswg/css-transitions/#application">Application of transitions</a>
+		does for CSS Transitions.
+	</p>
 
 <h3 id="timing-functions">
 Timing functions for keyframes</h3>
@@ -1124,7 +1131,7 @@ Working Group Resolutions that are pending editing</h2>
     	<li>2014-09-09 minutes (Antibes f2f)
     		<ul>
     		<li>Detail how/when keyframe values are computed; using <a href="http://lists.w3.org/Archives/Public/www-style/2014Aug/0132.html">G.beta in dbaron's mail</a>
-    		<li>Agreed that both transitions and animations animate all properties. css-transitions to define animation of non-interoperable/discrete values. They take their starting values below 50% timing function progress, and end values above
+    		<li><del>Agreed that both transitions and animations animate all properties. css-transitions to define animation of non-interoperable/discrete values. They take their starting values below 50% timing function progress, and end values above</del>
     		<li><del>Dynamic changes to animation properties/keyframes. Tab to propose resolution. (<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=14713">Bug 14713</a>)
     		<li><del>Negative animation-delay values apply against the active duration of the animation i.e. (animation-duration*animation-iteration-count). The delay can thus swallow iterations for which no iteration event will be fired. The start/end events are still fired. Even when delay == (-1*active_duration)
     		<li><del>Fire animation start/end events when animation-duration is zero, with 0 elapsedTime

css-animations/Overview.html

@@ -94,6 +94,8 @@ <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="cont
      <dd><span><a href="mailto:www-style@w3.org?subject=%5Bcss-animations%5D%20YOUR%20TOPIC%20HERE">www-style@w3.org</a> with subject line “<kbd>[css-animations] <var>… message topic …</var></kbd>” (<a href="http://lists.w3.org/Archives/Public/www-style/" rel="discussion">archives</a>)</span>
      <dt>Test Suite:
      <dd><a href="http://test.csswg.org/suites/css-animations-1_dev/nightly-unstable/">http://test.csswg.org/suites/css-animations-1_dev/nightly-unstable/</a>
+     <dt>Issue Tracking:
+     <dd><a href="#issues-index">Inline In Spec</a>
      <dt class="editor">Editors:
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:dino@apple.com">Dean Jackson</a> (<span class="p-org org">Apple Inc.</span>)
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:dbaron@dbaron.org">L. David Baron</a> (<span class="p-org org">Mozilla</span>)
@@ -294,6 +296,7 @@ <h2 class="no-num no-toc no-ref heading settled" id="contents"><span class="cont
      </ul>
     <li><a href="#property-index"><span class="secno"></span> <span class="content">Property Index</span></a>
     <li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
+    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
    </ul></div>
 
   <main>
@@ -632,6 +635,14 @@ <h2 class="heading settled" data-level="4" id="keyframes"><span class="secno">4.
 {T}{O}                         {return TO_SYM;}
 </pre>
 
+	
+   <p class="issue" id="issue-9bda05d2"><a class="self-link" href="#issue-9bda05d2"></a>
+		This specification needs to define
+		how the value is determined from the keyframes,
+		like the section on
+		<a href="http://dev.w3.org/csswg/css-transitions/#application">Application of transitions</a>
+		does for CSS Transitions.
+	</p>
 
 
    <h3 class="heading settled" data-level="4.1" id="timing-functions"><span class="secno">4.1. </span><span class="content">
@@ -1893,7 +1904,9 @@ <h2 class="heading settled" data-level="8" id="wg-resolutions-pending"><span cla
 
       <li>Detail how/when keyframe values are computed; using <a href="http://lists.w3.org/Archives/Public/www-style/2014Aug/0132.html">G.beta in dbaron’s mail</a>
 
-      <li>Agreed that both transitions and animations animate all properties. css-transitions to define animation of non-interoperable/discrete values. They take their starting values below 50% timing function progress, and end values above
+      <li>
+       <del>Agreed that both transitions and animations animate all properties. css-transitions to define animation of non-interoperable/discrete values. They take their starting values below 50% timing function progress, and end values above</del>
+       
 
       <li>
        <del>Dynamic changes to animation properties/keyframes. Tab to propose resolution. (<a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=14713">Bug 14713</a>)
@@ -2481,5 +2494,15 @@ <h2 class="no-num heading settled" id="idl-index"><span class="content">IDL Inde
   <a data-link-type="idl-name" href="#csskeyframerule">CSSKeyframeRule</a>? <a class="idl-code" data-global-name="CSSKeyframesRule<interface>/findRule(select)<method>" data-link-type="method" href="#dom-csskeyframesrule-findruleselect">findRule</a>(DOMString <a class="idl-code" data-global-name="CSSKeyframesRule<interface>/findRule(select)<method>/select<argument>" data-link-type="argument" href="#dom-csskeyframesrule-findruleselect-select">select</a>);
 };
 
-</pre></body>
+</pre>
+  <h2 class="no-num heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
+  <div style="counter-reset:issue">
+   <div class="issue">
+		This specification needs to define
+		how the value is determined from the keyframes,
+		like the section on
+		<a href="http://dev.w3.org/csswg/css-transitions/#application">Application of transitions</a>
+		does for CSS Transitions.
+	<a href="#issue-9bda05d2"> ↵ </a></div>
+  </div></body>
 </html>

css-transitions/Overview.bs

@@ -28,7 +28,7 @@ Editor: Chris Marrin, Apple Inc, cmarrin@apple.com
 Issue Tracking: Bugzilla bugs for this level 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
 Issue Tracking: Bugzilla bugs for all levels https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&product=CSS&component=Transitions&resolution=---
 Abstract: CSS Transitions allows property changes in CSS values to occur smoothly over a specified duration.
-Status Text: <strong>This document</strong> is expected to be relatively close to last call.  While some issues raised have yet to be addressed, new features are extremely unlikely to be considered for this level.
+Status Text: <strong>This document</strong> is expected to be relatively close to last call.  While some issues raised have yet to be addressed, new features are extremely unlikely to be considered for this level. <p>The following behaviors are at risk: <ul><li><a href="#discrete-interpolation-at-risk">Interpolation in steps of property types that cannot be interpolated</a></li></ul>
 Ignored Terms: float
 </pre>
 <!-- FIXME: font-size and font-weight link defaults don't work -->
@@ -1245,6 +1245,15 @@ url: https://html.spec.whatwg.org/multipage/infrastructure.html#concept-event-di
         Animation of property types
       </span></h2>
 
+      <p>
+        Some property types can be interpolated,
+        which means they can animate smoothly from one value to another.
+        Other property types cannot, and thus animate only in a single
+        step from one value to the other.
+      </p>
+
+      <h3 id="interpolated-types">Animation of interpolated property types</h3>
+
       <p>
         When interpolating between two values,
         <var>V</var><sub>start</sub> and <var>V</var><sub>end</sub>,
@@ -1389,6 +1398,30 @@ url: https://html.spec.whatwg.org/multipage/infrastructure.html#concept-event-di
       of shorthand properties and the ''all'' value is applied to any
       properties (in the shorthand) that can be animated.</p>
 
+      <h3 id="step-types">Animation in steps of other property types</h3>
+
+      <p>
+        When interpolating between two values that cannot be interpolated,
+        <var>V</var><sub>start</sub> and <var>V</var><sub>end</sub>,
+        interpolation is done using the output <var>p</var> of the timing function.
+        If <var>p</var> is less than 0.5, then the
+        result of the interpolation is
+        <var>V</var><sub>start</sub>;
+        if <var>p</var> is greater than or equal to 0.5, then the
+        result of the interpolation is
+        <var>V</var><sub>end</sub>.
+      </p>
+
+      <p class="note" id="discrete-interpolation-at-risk">
+        This is a recent change to which implementations have
+        not yet updated.  (Prior to the change CSS Transitions
+        and CSS Animations did not run on such changes.)  It's
+        possible that it won't be compatible with existing Web content.
+        If that is the case, the problem may be mitigated by restricting
+        this behavior only to CSS Animations (and not to CSS Transitions),
+        and/or restricting it to step timing functions.
+      </p>
+
       <h2 id="animatable-properties"><span id="animatable-properties-">
         Animatable properties
       </span></h2>
@@ -1402,15 +1435,21 @@ url: https://html.spec.whatwg.org/multipage/infrastructure.html#concept-event-di
       when the values of that property can be interpolated
       by referring to the definitions of property types
       in the <a href="#animatable-types">previous section</a>.
-      Values are animatable when
+      The animated value is interpolated from the from and to values when
       both the from and the to values of the property have the type described.
       (When a composite type such as "length, percentage, or calc" is listed,
       this means that both values must fit into that composite type.)
       When multiple types are listed in the form "either A or B",
       both values must be of the same type to be interpolable.</p>
 
+      <p>Otherwise, since the from and to values cannot be interpolated,
+      the animation is done <a href="#step-types">in a single step</a>.</p>
+
+      <p>The 'transition-*' properties defined in this specification do
+      not undergo transitions.</p>
+
       <p>For properties that exist at the time this specification was
-      developed, this specification defines whether and how they are
+      developed, this specification defines how they are
       animated.  However, future CSS specifications may define
       additional properties, additional values for existing properties,
       or additional animation behavior of existing values.  In order to
@@ -1428,6 +1467,12 @@ url: https://html.spec.whatwg.org/multipage/infrastructure.html#concept-event-di
       the property animates.  Such definitions override those given in
       this specification.</p>
 
+      <p class="issue">
+        It no longer makes sense for this line to be called
+        "Animatable".  It should probably be renamed to "Interpolation",
+        and the "no" value renamed to "discrete" or "in steps".
+      </p>
+
       <h3 id="animatable-css"><span id="properties-from-css-">
         Properties from CSS
       </span></h3>
@@ -1634,6 +1679,7 @@ url: https://html.spec.whatwg.org/multipage/infrastructure.html#concept-event-di
 dated 19 November 2013</a>:</p>
 
 <ul>
+  <li>Values that cannot be interpolated are transitioned when the timing function crosses its midpoint, instead of not running transitions and changing immediately.</li>
   <li>Canceling and interrupting of running transitions is defined much more precisely.  This includes the after-change style no longer including styles from CSS Transitions.</li>
   <li>Completion of transitions is defined somewhat more precisely.</li>
   <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.</li>