[maccatalyst] canvas not cleared of previous drawings

[spouliot]

Current behavior

From #16690 (comment)

updates on live charts do not seem to clear previous drawings (unless a redraw is made)

@spouliot On the LiveCharts side, clearing the canvas is something we do depending on the UI framework, some frameworks require it, some frameworks don't.

In the specific case of Uno, all the supported platforms do not require to clear the canvas, but on catalyst it seems that it behaves different, should this be handled in the LiveCharts side?

Expected behavior

This should be identical with other Uno backends

How to reproduce it (as minimally and precisely as possible)

The LiveCharts sample was showing the issue (see original issue)

Workaround

No response

Works on UWP/WinUI

Yes

Environment

No response

NuGet package version(s)

No response

Affected platforms

Skia (macOS)

IDE

No response

IDE version

No response

Relevant plugins

No response

Anything else we need to know?

No response

[spouliot]

This works fine on netX.X-desktop (macOS) but the background is incorrect on netX.X-maccatalyst.

The "Show menu" is under the window title bar (requires an offset for it, but it's not related to this issue).

The chart background is black and there are several updates without the background being cleared.

[spouliot]

The weird thing is that the netX.X-ios version behave correctly...

The "Show menu" button is visible (even if above the top status bar).

The background is white and is chart updates are correct (the background is cleared between updates).

[spouliot]

Inside livecharts2's SkiaSharpDrawingContext.OnBeginDraw things behave identically on both desktop and maccatalyst.

IOW in both cases clearOnBeginDraw is true, so Canvas.Clear() is called and Background is empty so nothing is drawn over.

So nothing in LiveChart2, nothing in Uno... so where ?

SkiaSharp as it uses IOS instead of __IOS__ to set UIView.Opaque to false. IOW this only applies to iOS, not Catalyst. Once updated it works fine.

[spouliot]

The SkiaSharp PR was merged and the fix will be available once a new lease of SkiaSharp is out.