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[web-anim] Web animations minutes, 14 February 2013

From: Brian Birtles <bbirtles@mozilla.com>
Date: Fri, 15 Feb 2013 09:46:11 +1100
Message-ID: <511D6933.7060802@mozilla.com>
To: "public-fx@w3.org" <public-fx@w3.org>
Web animations minutes, 14 February 2013

Etherpad: https://etherpad.mozilla.org/ep/pad/view/ro.bMYQI4aMCGp/latest
Present: Dmitry, Doug, Shane, Steve, Brian

Agenda:
1. Timing
2. Pausing on pagehide / unload
3. getCurrentAnimations()
4. Effect templating
5. GroupedAnimationEffect


1. TIMING
=========

Straw man proposal: 
http://www.w3.org/Graphics/fx/wiki/Web_Animations/Shared_Timing

Steve's getComputedTiming suggestion:

TimedItem
   - timing
     - duration
     - playbackRate
     - iterationCount
     - ...
   - getComputedTiming()

One suggestion:

  anim.currentIteration
  anim.endTime
  anim.startDelay
  anim.iterationStart
  anim.iterationCount
  anim.iterationDuration
  anim.activeDuration
  anim.fillMode
  anim.playbackRate
  anim.direction
  anim.timingFunction
  anim.useIntrinsicDuration()
  anim.usePercentageDuration()

Another suggestion:

  TimedItem:
    double startDelay;
    double iterationStart;
    double iterationCount;
    (double or DOMString) iterationDuration;
    FillMode fillMode;
    double playbackRate;
    PlaybackDirection direction;
    TimingFunction timingFunction;
    ComputedTiming getComputedTiming();

  Interface ComputedTiming
    double startTime; // Need for seq children in particular
    double endTime;
    double currentIteration;
    double activeDuration;
    FillMode fillMode;
    double playbackRate;
    PlaybackDirection direction;
    TimingFunction timingFunction;

Notes:
- ComputedTiming is different to the Timing dictionary since it provides 
some members you can't set in the Timing dictionary (such as the 
startTime) and because values in ComputedTiming are always resolved 
values (e.g. doubles) rather than allowing magic values
- activeDuration is not currently on TimedItem. It will be added there 
when we allow overriding it. This allows us to make its type (double or 
String) without breaking content (as might happen if it were double to 
begin with)
- FillMode is returned in ComputedTiming since we want to encourage 
people to read values from there in case we make FillMode a 
calculated/intrinsic value in the future. Likewise for playbackRate, 
direction, timingFunction.
- In future playbackRate may be overrideable, e.g. "10px/s"
- Feels like this is a bit heavy-handed when most of the members will be 
identical to those on TimedItem all the time.

However, WebIDL does not allow (double or DOMString) as a union type 
since double and DOMString are not distinguishable:

   http://www.w3.org/TR/WebIDL/#dfn-distinguishable

(double or ExtendedDuration) duration

dictionary ExtendedDuration {
     DurationType type;
     DOMString spec;
};

enumeration DurationType {
     "intrinsic",
     "calc",
     "percentage"
};

anim.iterationDuration = { type: "intrinsic" };
anim.iterationDuration = { type: "calc", spec: "calc(20% + 1)" };
anim.iterationDuration = 2;

Try again:

(double or ExtendedDuration) duration

dictionary ExtendedDuration {
     DOMString dur;
};

anim.iterationDuration = { dur: "intrinsic" };
anim.iterationDuration = { dur: "calc(20% + 1s)" };
anim.iterationDuration = 2;

In SVG:
<animate dur="calc(20% + 1s)">
<animate dur="2s">

Alternatively just have:
   any duration;

And describe handling that effectively does (DOMString or double). Is 
this possible?
This is what setTimeout() does.

After discussion with Cameron it appears that is has recently been 
decided that in WebIDL you can overload with primitives vs DOMStrings 
and so it may be that it is allowed in unions too.

This approach has been accepted as a compromise we’re all happy with.


2. PAGE HIDE / UNLOAD BEHAVIOUR
===============================

Should animations pause when:
a) A link is clicked to navigate to another page? i.e. if you click back 
does it resume?
b) The page goes into a background tab

a) A link is clicked to navigate to another page.

What does video do?

In Firefox, if you navigate to another page and go back, the video 
resumes from where you left off.
In Webkit and Opera, the video starts from the beginning.

Most browsers have a bfcache / Page Cache / Fast Navigation Cache. Can 
we spec that if the page is cached it is paused? A MAY requirement?

b) The page goes into a background tab

General agreement that animations should NOT be paused in this case. If 
you actually want this behaviour, you can use onpagehide etc. to pause 
all the animations.

Discussed how on some mobile UAs javascript in background tabs can be 
suspended in order to save battery. Likewise, we might expect animations 
to be throttled so low they effectively get no samples.

In SVG there have been similar issues where an animation that has not 
been sampled for a long time (e.g. because the computer was asleep) 
produces a major performance hit when the computer wakes up and we try 
to "catch up" the animation including firing 1000s of events. This 
suggests the implementation should be allowed to pause animations in 
such circumstances.

We could add a wakeup / sync event later to indicate that animation time 
drifted from wallclock time.


3. getCurrentAnimations()
=========================

Current?
   Is presently defined to include all animations that are either 
running (in the active interval) or yet-to-run. The definition needs to 
be reworked to include animations that have finished but are in a group 
that is still running since these animations might run again (e.g. if 
it’s iterating).

getCurrentAnimations returns animations, but sometimes we want the set 
of active players
We could have getActivePlayers() and 
Player.getCurrentAnimations(optional element)

Use cases:
① As a web author, I want to extend an animation written in CSS, by 
adding a JavaScript animation effect
   ○ Element.getCurrentAnimations():sequence<Animation>

② As a web author, I want to remove all animations targetting an element 
/ fragment to serialize the static state of the content
   ○ Element.getCurrentAnimationPlayers()->cancel()
   ○ Is there a way to do this without killing other animations in the 
‘scene’?
     ◊ foreach [ animation.effect = undefined ]

③ As a web author, I want to find the green glow animation on a button, 
and make it glow red since the deadline is approaching
   ○ Element.getCurrentAnimations():sequence<Animation>, walk through 
and find the one with the right animation effect, change the effect

④ As a web author, I want to pause/cancel/change-playback-rate for all 
animations when some event occurs (eg. when I show a modal dialog)
   ○ Document.getCurrentAnimations():sequence<Animation> *could* do this 
but a list of players would be much more suitable.
   ○ Do you actually want to pause transitions too?
   ○ How about Document.timeline.getCurrentPlayers()?

⑤ As a library/tool developer, I want to look up all the animations 
targetting an element so I can produce a debug view
   ○ Element.getCurrentAnimations():sequence<Animation>, just iterate 
over and display
   ○ Element.getCurrentAnimationPlayers() if you want to look at the scenes.

⑥ As a web author, I have a running animation that scrolls the view, and 
I want to inspect the progress of the animation so I know where to add 
another graphic/animation such that it appears on screen.
   ○ Element.getCurrentAnimations() → find appropriate animation → 
getComputedTiming()

⑦ As a web author, I have a running animation and I want to create a new 
target element and apply a new animation to the new target that picks up 
where the previous animation left off.
   ○ Element.getCurrentAnimations() → do stuff

⑧ As a tool developer, I want to show a timeline of all animations in 
the document with the ability to inspect them.
   ○ Document.timeline.getPlayers()->timedItem

Proposal:

   Document.timeline.getCurrentPlayers():sequence<Player>
   Element.getCurrentAnimations():sequence<Animation>
   Element.getCurrentAnimationPlayers():sequence<Player>

Other ideas considered:

   Document.timeline.getCurrentScenes():sequence<TimedItem>
   Player.getCurrentAnimations(optional Element):sequence<Animation>


4. EFFECT TEMPLATING
====================

Agreed to model basic keyframe effect templating inside the CSS 
integration specification. This would involve keyframe effects being 
able to have parent effects, and the list of used keyframes being the 
union of the local and parent lists.

Doug presented an alternative in which incomplete CSS keyframe 
specifications lead to animations represented by par groups. Some 
concern was expressed about returning ParGroup objects when there are no 
par groups in the markup.


5. GroupedAnimationEffect
=========================

1. Drop GroupedAnimationEffect
2. Keep merge in operator enum

Brian was unsure about if we should expose merge at the API level or 
just provide special behaviour that basically does a merge when you have 
no zero keyframe animation much like SVG’s to-animation or like CSS to 
some extent. We think it's ok to expose merge for now and see how 
developers react. If it is problematic we can review how to approach this.

There is consensus on supporting merge within the model.

Shane briefly discussed potential future extensions to merge and grouping:
  * parameterized merge with optional start and end values (in seconds 
or percentages)
  * using either TimingGroups or named compositorGroups to group 
compositor stack entries together. There was some trouble with this so 
we need to think about it more. Specifically: Brian is uncomfortable 
using TimingGroups as compositor groups, and if we use named 
compositorGroups we need some way to specify the operator for the groups.


Next meeting: Fri 15 Feb 9:00 AEDST @ Google Sydney

Past meetings: http://www.w3.org/Graphics/fx/wiki/Web_Animations/Meetings
Received on Thursday, 14 February 2013 22:46:43 GMT

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