Fix iOS Dispatcher

[maxkatz6]

What does the pull request do?

Two major changes:

1. Replaces kCFRunLoopCommonModes with kCFRunLoopDefaultMode on loop observer and timer. Original code was copy-pasted from our macOS backend, where we used kCFRunLoopCommonModes. But apparently it's a no-op on iOS. This was an actual bug in our backend, as the timer wasn't ticking basically.
2. Replaces delegates with function pointers where in dispatcher code. And ensuring that we don't have any runtime marshaling with dll imports. Both should result in less overhead.

Fixed issues

I have not tested all of these issues, but only animations+timer related. Let me know if any of these issues is still reproducible.

Fixes #13594
Fixes #13110
Fixes #13029
Fixes #11696
Fixes #13941

[avaloniaui-bot]

You can test this PR using the following package version. 11.1.999-cibuild0042885-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[avaloniaui-bot]

You can test this PR using the following package version. 11.1.999-cibuild0043034-beta. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[cangunaydin]

don't know if this is directly related but #13941 is still not fixed.
InvalidateVisual is still triggering with very much latency, sometimes it is not even triggered.
Can be related with dispatcher but not sure.
i have created a minimal repro with the problem if you want to check.
https://github.com/cangunaydin/avalonia-customskia-ios-bug

[maxkatz6]

@cangunaydin please use a newer invalidation APIs: TopLevel.GetTopLevel(thisControll).RequestAnimationFrame(callback). You can use InvalidateVisual as a callback.

In short, Dispatcher shouldn't be used to sync with framerate. It was an old approach of 0.10 version. RequestAnimationFrame will actually sync with the framerate.

[cangunaydin]

Hello again,
I tried but it doesn't help. same behavior. check the image 6 or 7 ticks happening in 30secs.

[maxkatz6]

Can you test on a real device? .NET runtime is rather slow in the simulator.
If not, I can try on the next week.

[maxkatz6]

Either way, it doesn’t look related to the old issue. Previously dispatcher wouldn’t raise any timer ticks at all. In your case there is something ticking

[cangunaydin]

sure i will try it on the real device. Yes you are right it is not related with the old issue. But don't think the behavior will change on real device. The weird part is like 2 days ago it seems it was working with dispatcher, i was playing with it and it is broken now :) maybe it can be related with whatever i did. But same sample works fine on android emulator
if it doesn't work with real device, should i open a new issue instead?

[cangunaydin]

I have tested it on iphone 12, it is much more better. But still it is around 28fps. It seems like sth else is slowing it down.
on android emulator it is around 60fps, on my old samsung galaxy tablet Galaxy Tab A (2016) it is only 2fps.

[maxkatz6]

@cangunaydin so, I have 60 fps on iPhone 15. Though there shouldn't be such difference, unless you have limited FPS or there some another problem with configuration.

1. How do you measure FPS? You should use TopLevel.GetTopLevel(this).RendererDiagnostics.DebugOverlays |= RendererDebugOverlays.Fps;.
2. Simulator apps are known to be much slower. They also run JIT interpreter. It's still surprising that iphone 12 has such bad fps.
3. You can try to enable Metal rendering in the latest master (was merged today):

            .With(new iOSPlatformOptions
            {
                RenderingMode = new [] { iOSRenderingMode.Metal }
            })

[cangunaydin]

Hello @maxkatz6 ,
I have tried with

 .With(new iOSPlatformOptions
            {
                RenderingMode = new [] { iOSRenderingMode.Metal }
            })

and it increased to 60fps. weird though why it has so much difference with opengl.
I was using my own calculation for fps.

But it has the same value with opLevel.GetTopLevel(this).RendererDiagnostics.DebugOverlays |= RendererDebugOverlays.Fps;
is there a way to set the fps overlay somewhere else than safe areas?

[maxkatz6]

Good to know that Metal helps.

No, I don’t think it’s possible to move fps counter.