Created attachment 341645 [details] Testcase Compare animations with linear timing function VS steps timing function.

Created attachment 341659 [details] Patch

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

Created attachment 342247 [details] Patch Improved test.

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>

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)?

<rdar://problem/45237786>

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

<rdar://problem/45237815>

(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).

(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)

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

(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

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

(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

(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).