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Initial attempt at supporting negative infinity start delay (issue #48) #87

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Initial attempt at supporting negative infinity start delay (issue #48) #87

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100 changes: 87 additions & 13 deletions Overview.src.html
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Original file line number Diff line number Diff line change
Expand Up @@ -1647,10 +1647,14 @@ <h4 id="the-active-interval">The active interval</h4>
In addition to the <a lt="animation effect start time">start
time</a>, an <a>animation effect</a> also has a <dfn>start delay</dfn>
which is an offset from the <a lt="animation effect start time">start time</a>.
The <a>start delay</a> is represented a real number including positive and
negative infinity.
<!-- @ifdef INCLUDE_GROUPS -->
Unlike the <a lt="animation effect start time">start time</a> which
is determined by the <a>parent group</a>, the <a>start
delay</a> is a property of the <a>animation effect</a> itself.

<!-- @endif --><!-- @ifndef INCLUDE_GROUPS -->
<!-- @endif -->

The lower bound of the <a>active interval</a> of an <a>animation
Expand Down Expand Up @@ -1874,11 +1878,19 @@ <h4 id="animation-effect-phases-and-states">Animation effect phases and
3. the <a>animation effect</a>'s <a>local time</a> is <em>less
than</em> the sum of its <a>start delay</a> and <a>active
duration</a>.
If the <a>start delay</a> is negative infinity, and the
<a>active duration</a> is positive infinity, the sum of the <a>start
delay</a> and <a>active duration</a> is positive infinity for the purpose
of this comparison.

An <a>animation effect</a> is in the <dfn>after phase</dfn> if the
animation effect's <a>local time</a> is not <a>unresolved</a> and is
<em>greater than or equal</em> to the sum of its <a>start delay</a>
and <a>active duration</a>.
As with the <a>active phase</a>, if the <a>start delay</a> is negative infinity
and the <a>active duration</a> is positive infinity, then, for the purposes of
this comparison, their sum is positive infinity and, as such, the <a>animation
effect</a> will never enter the <a>after phase</a>.

An <a>animation effect</a> is <dfn>in play</dfn> if <em>all</em>
of the following conditions are met:
Expand Down Expand Up @@ -2110,6 +2122,12 @@ <h4 id="controlling-iteration">Controlling iteration</h4>
The <a>iteration start</a> is a finite real number greater than or
equal to zero.

For an <a>animation effect</a> whose <a>start delay</a> is negative infinity and
<a>iteration count</a> is positive infinity, the <a>iteration start</a>
determines the offset into the current iteration when the <a>local time</a> is
zero. As such, only the fraction portion of the <a>iteration start</a> is
significant in this case.

The behavior of these parameters is defined in the calculations in <a
href="#core-animation-effect-calculations" section></a>.

Expand Down Expand Up @@ -2450,9 +2468,15 @@ <h5 id="calculating-the-active-time">Calculating the active time</h5>

The <dfn>active time</dfn> is based on the <a>local time</a>
and <a>start delay</a>.
However, it is only defined when the <a>animation effect</a> should
produce an output and hence depends on its <a>fill mode</a> and
phase
Note that since the <a>start delay</a> may be negative infinity, the
<a>active time</a> may be positive infinity. When the <a>start delay</a> is
positive infinity, the <a>animation effect</a> never enters the <a>active
phase</a>, hence the reverse case of <a>active time</a> becoming negative
infinity never occurs.

The <a>active time</a> is only a <a lt=unresolved>resolved</a> time when the
<a>animation effect</a> should produce an output and hence depends on its
<a>fill mode</a> and phase
<!-- @ifdef INCLUDE_GROUPS -->
as well as the phase of its <a>parent group</a>, if any,
<!-- @endif -->
Expand Down Expand Up @@ -2569,7 +2593,18 @@ <h5 id="calculating-the-scaled-active-time">Calculating the scaled active time</
an <a>unresolved</a> <a>time value</a>.

<!-- @ifdef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->
2. Return the scaled active time based on the
2. If the <a>active time</a> is positive infinity, return the <a>active
time</a>.

Note: The <a>active time</a> is only positive infinity in the case of
a <a>start delay</a> of negative infinity and an <a>iteration duration</a>
of infinity. In this case, positive infinity is a reasonable value for
the <a>scaled active time</a> (regardless of the value of the
<a lt="animation effect playback rate">playback rate</a>) because special
handling of the <a>iteration time</a> is performed in this case
without using the <a>scaled active time</a>.

3. Return the scaled active time based on the
<a lt="animation effect playback rate">playback rate</a> as
follows,

Expand All @@ -2582,6 +2617,8 @@ <h5 id="calculating-the-scaled-active-time">Calculating the scaled active time</
&times; <a lt="animation effect playback rate">playback
rate</a> + <a>start offset</a></code>.

If <a>active time</a> is positive infinity and <a>active duration</a>

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This looks like a sentence fragment. Is there meant to be more, or is this meant to be another dt for the following dl?

: If the <a lt="animation effect playback rate">playback
rate</a> is zero,
:: Return <a>start offset</a>.
Expand All @@ -2607,9 +2644,24 @@ <h5 id="calculating-the-iteration-time">Calculating the iteration time</h5>
1. If the <a>scaled active time</a> is <a>unresolved</a>,
return <a>unresolved</a>.

2. If the <a>iteration duration</a> is zero, return zero.
2. If the <a>iteration duration</a> is zero or infinity, return zero.

3. If the <a>start delay</a> is negative infinity, return the result of
evaluating<!-- @ifdef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->
<code>(<a>animation effect playback rate</a> &times; <a>local time</a> +
(<a>iteration start</a> % 1) &times; <a>iteration duration</a>) %
<a>iteration duration</a></code>.

<!-- @endif --><!-- @ifndef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->
<code>(<a>local time</a> + (<a>iteration start</a> % 1) &times;
<a>iteration duration</a>) % <a>iteration duration</a></code>.

<!-- @endif -->

Note: In this case the <a>iteration count</a> must be positive infinity or
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Don't use MUST here; even though it's in a note and thus by definition not normative, it's still confusing. Rephrase as "in this case the iteration count is guaranteed to be positive infinity, as otherwise the scaled active time would be unresolved".

else the <a>scaled active time</a> would be <a>unresolved</a>.

3. If <code><a>scaled active time</a> - <a>start
4. If <code><a>scaled active time</a> - <a>start
offset</a></code> is equal to the<!-- @ifdef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->
<a>repeated duration</a>,<!-- @endif --><!-- @ifndef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->
<a>active duration</a>,<!-- @endif -->
Expand All @@ -2618,7 +2670,7 @@ <h5 id="calculating-the-iteration-time">Calculating the iteration time</h5>
% 1</code> is zero,
return the <a>iteration duration</a>.

4. Otherwise, return <code><a>scaled active time</a>
5. Otherwise, return <code><a>scaled active time</a>
% <a>iteration duration</a></code>.

<h4 id="calculating-the-current-iteration">Calculating the current iteration</h4>
Expand All @@ -2645,6 +2697,9 @@ <h4 id="calculating-the-current-iteration">Calculating the current iteration</h4
1. Otherwise, return
<code>ceil(<a>iteration start</a> + <a>iteration count</a>) - 1</code>.

1. If the <a>active time</a> is positive infinity, return positive
infinity.

1. If the <a>iteration time</a> equals the <a>iteration
duration</a>, return <code><a>iteration start</a> +
<a>iteration count</a> - 1</code>.
Expand Down Expand Up @@ -2716,18 +2771,32 @@ <h4 id="calculating-the-directed-time">Calculating the directed time</h4>

1. Let <var>d</var> be the <a>current iteration</a>.

2. If <a>playback direction</a> is
2. If <var>d</var> is positive infinity, let <var>d</var> be the
result of evalulating:

<blockquote>
<code><!-- @ifdef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->

floor((<a lt="animation effect playback rate">playback rate</a>
&times; <a>local time</a> +
<!-- @endif --><!-- @ifndef INCLUDE_ANIMATION_NODE_PLAYBACKRATE -->
floor((<a>local time</a> +
<!-- @endif -->
(<a>iteration start</a> % 1) &times; <a>iteration duration</a>) /
<a>iteration duration</a>)</code></blockquote>

3. If <a>playback direction</a> is
<code>alternate-reverse</code> increment
<var>d</var> by 1.

3. Issue: There used to be a step here which seemed to be adding
4. Issue: There used to be a step here which seemed to be adding
special handling for filling when the effect ends on
a repeat boundary but it seems like that is taken care
of by the calcuation of <a>iteration time</a> and
<a>current iteration</a>.
Is anything actually needed here?

4. If <code><var>d</var> % 2 == 0</code>, let the
5. If <code><var>d</var> % 2 == 0</code>, let the
<var>current direction</var> be forwards, otherwise let
the <var>current direction</var> be reverse.
If <var>d</var> is infinity, let the <var>current direction</var>
Expand Down Expand Up @@ -3397,6 +3466,9 @@ <h4 id="calculating-the-time-fraction">Calculating the time fraction</h4>

</div>

: If the <a>iteration duration</a> is positive infinity,
:: Return <code><a>iteration start</a> % 1</code>.

: Otherwise,
:: Return <a>transformed time</a> / <a>iteration duration</a>.

Expand Down Expand Up @@ -5304,7 +5376,7 @@ <h3 id="the-animationtimingreadonly-interface">The <code>AnimationEffectTimingRe

<pre class="idl">
interface AnimationEffectTimingReadonly {
readonly attribute double delay;
readonly attribute unrestricted double delay;
readonly attribute double endDelay;
readonly attribute FillMode fill;
readonly attribute double iterationStart;
Expand Down Expand Up @@ -5465,7 +5537,7 @@ <h3 id="the-animationtiming-interface">The <code>AnimationEffectTiming</code> in

<pre class='idl'>
interface AnimationEffectTiming : AnimationEffectTimingReadonly {
inherit attribute double delay;
inherit attribute unrestricted double delay;
inherit attribute double endDelay;
inherit attribute FillMode fill;
inherit attribute double iterationStart;
Expand Down Expand Up @@ -5549,7 +5621,7 @@ <h3 id="the-animationtiminginput-dictionary">The <code>AnimationEffectTimingProp

<pre class='idl'>
dictionary AnimationEffectTimingProperties {
double delay = 0;
unrestricted double delay = 0;
double endDelay = 0;
FillMode fill = "auto";
double iterationStart = 0.0;
Expand Down Expand Up @@ -7308,6 +7380,8 @@ <h2 id="changes-since-last-publication">Changes since last publication</h2>
asynchronous play/pause/reverse operations.
* Renamed animation nodes to <a>animation effects</a> and what were previously
known as an animations to <a>keyframe effects</a>.
* Allowed the <a>start delay</a> of an <a>animation effect</a> to be positive
or negative infinity.
* Deferred group effects (previously known as animation groups) to a <a
href="https://w3c.github.io/web-animations/level-2/">subsequent level</a>.
Deferring this feature also lead to the following simplifications.
Expand Down