[iOS] Transformation matrix not preserved when pausing complex animation with Bézier timing function

[Frédéric Wang (:fredw)]

Extracted from bug 170784. With the patch for bug 170784, http://codepen.io/anon/pen/bWGobG can be paused but the rotation angle is lost.

[Frédéric Wang (:fredw)]

Created attachment 341645 [details]
Testcase

Compare animations with linear timing function VS steps timing function.

[Frédéric Wang (:fredw)]

Created attachment 341659 [details]
Patch

[Frédéric Wang (:fredw)]

Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/11279

[Frédéric Wang (:fredw)]

Created attachment 342247 [details]
Patch

Improved test.

[Frédéric Wang (:fredw)]

Created attachment 342666 [details]
Another testcase

So I tried to compare what happens on macOS and iOS and basically they both use CALayer's addAnimation to add two animations (translate and rotate) and later replace them by a zero-speed copy. Below are the output in PlatformCALayerCocoa::addAnimationForKey and PlatformCAAnimationRemote's addAnimationToLayer for the attached testcase. I don't see any obvious difference so my guess would be a bug in the iOS-implementation of the CALayer classes.

== macOS ==

(lldb)  p propertyAnimation.valueFunction.name
(__NSCFConstantString *) $30 = 0x00007fffadc428c0 @"translate"
(lldb) po propertyAnimation
<CABasicAnimation:0x7f8ba545a2c0; delegate = <WebAnimationDelegate: 0x7f8ba5630530>; toValue = (
    90,
    0,
    0
); fromValue = (
    0,
    0,
    0
); valueFunction = <CAValueFunction: 0x7f8ba562ea20>; timingFunction = linear; additive = 0; removedOnCompletion = 0; fillMode = forwards; autoreverses = 0; repeatCount = 1; timeOffset = 2.30686; speed = 0; duration = 5; WKPlatformCAAnimationExplicitBeginTimeFlag = false; beginTime = 4023.49; keyPath = transform>

(lldb)  p propertyAnimation.valueFunction.name
(__NSCFConstantString *) $34 = 0x00007fffadc42800 @"rotateZ"
(lldb) po propertyAnimation
<CABasicAnimation:0x7f8ba560c010; delegate = <WebAnimationDelegate: 0x7f8ba5630530>; toValue = 3.1415927410125732; fromValue = 0.0; valueFunction = <CAValueFunction: 0x7f8ba562ead0>; timingFunction = linear; additive = 1; removedOnCompletion = 0; fillMode = forwards; autoreverses = 0; repeatCount = 1; timeOffset = 2.30686; speed = 0; duration = 5; WKPlatformCAAnimationExplicitBeginTimeFlag = false; beginTime = 4023.49; keyPath = transform>

== iOS ==

(lldb) p properties.valueFunction
(const ValueFunctionType) $10 = Translate
(lldb) po caAnimation.get()
<CABasicAnimation:0x7fd694f9fd50; delegate = <WKAnimationDelegate: 0x7fd694eded40>; valueFunction = <CAValueFunction: 0x7fd694fd4d70>; fillMode = forwards; additive = 0; removedOnCompletion = 0; autoreverses = 0; speed = 0; repeatCount = 1; timeOffset = 2.30493; duration = 5; beginTime = 4494.56; timingFunction = linear; toValue = (
    90,
    0,
    0
); fromValue = (
    0,
    0,
    0
); keyPath = transform>

(lldb) p properties.valueFunction
(const ValueFunctionType) $12 = RotateZ
(lldb) po caAnimation.get()
<CABasicAnimation:0x7fd694feb1c0; delegate = <WKAnimationDelegate: 0x7fd694eded40>; valueFunction = <CAValueFunction: 0x7fd694fd43d0>; fillMode = forwards; additive = 1; removedOnCompletion = 0; autoreverses = 0; speed = 0; repeatCount = 1; timeOffset = 2.30493; duration = 5; beginTime = 4494.56; timingFunction = linear; toValue = 3.1415927410125732; fromValue = 0.0; keyPath = transform>

[Frédéric Wang (:fredw)]

Just tried again after https://trac.webkit.org/changeset/233460/webkit and animations of the testcases can be paused but the rotation angle is lost. I'm testing a trunk build on the iOS simulator using the public SDK. As said in comment 5, I don't see any difference between iOS and macOS regarding how animations are set on the CALayer, so I wonder whether the issue is actually in proprietary code.

@Antoine Quint: Do you see the same bug with your setup? Do you think it's fixable in WebKit (maybe with a hack like the bug7311367Workaround function in GraphicsLayerCA)?

[Radar WebKit Bug Importer]

<rdar://problem/45237786>

[Simon Fraser (smfr)]

https://codepen.io/anon/pen/bWGobG still shows this bug on iOS.

[Radar WebKit Bug Importer]

<rdar://problem/45237815>

[Frédéric Wang (:fredw)]

(In reply to Simon Fraser (smfr) from comment #8)
> https://codepen.io/anon/pen/bWGobG still shows this bug on iOS.

The bug still happens with the latest beta iOS 12.2 (January 24).

[Frédéric Wang (:fredw)]

(In reply to Frédéric Wang (:fredw) from comment #10)
> (In reply to Simon Fraser (smfr) from comment #8)
> > https://codepen.io/anon/pen/bWGobG still shows this bug on iOS.
> 
> The bug still happens with the latest beta iOS 12.2 (January 24).

Same in iOS beta 12.3 (May 13)

[Simon Fraser (smfr)]

Doesn't seem to reproduce in Safari Tech Preview 82.

[Frédéric Wang (:fredw)]

(In reply to Simon Fraser (smfr) from comment #12)
> Doesn't seem to reproduce in Safari Tech Preview 82.

You mean macOS? This bug is iOS-specific

[Frédéric Wang (:fredw)]

In iOS 13 beta 2, the rotation angle seems to be preserved but the translation is lost.

[Frédéric Wang (:fredw)]

(In reply to Frédéric Wang (:fredw) from comment #14)
> In iOS 13 beta 2, the rotation angle seems to be preserved but the
> translation is lost.

Same in iOS 13 beta 3

[Frédéric Wang (:fredw)]

(In reply to Frédéric Wang (:fredw) from comment #15)
> (In reply to Frédéric Wang (:fredw) from comment #14)
> > In iOS 13 beta 2, the rotation angle seems to be preserved but the
> > translation is lost.
> 
> Same in iOS 13 beta 3

This bug is fixed in iOS 14 beta (18A5301v).