Add support for SkiaVisual

[jeromelaban]

What would you like to be added

Add support for a composition level SkiaVisual, which can allow third parties to use SkiaSharp in a constrained visual.

Why is this needed

Faster implementation of the SKXamlCanvas, and hardware acceleration for such controls, or custom visuals based on SkiaVisual.

For which platform

No response

Anything else we need to know?

Such an API cannot be provided at the XAML level for threading concerns.

A similar implementation for a visual is TextVisual, for which there's currently no publicly available API.

[lindexi]

Awesome, thank you @jeromelaban . I'm looking forward to this feature

---

Why not SKXamlCanvas?

Because the SKXamlCanvas is working the hack thing. The SKXamlCanvas will render and then copy to WriteableBitmap to show.

See https://github.com/mono/SkiaSharp/blob/9274aeec807fd17eec2a3266ad4c2475c37d8a0c/source/SkiaSharp.Views.Uno/SkiaSharp.Views.Uno.WinUI.Skia/SKXamlCanvas.Skia.cs#L27

The SKXamlCanvas have to copy the pixel data to WriteableBitmap :

	public partial class SKXamlCanvas : Canvas
	{
		private void DoInvalidate()
		{
			...

			var info = CreateBitmap(out var unscaledSize, out var dpi);

			using (var surface = SKSurface.Create(info, pixelsHandle.AddrOfPinnedObject(), info.RowBytes))
			{
				...

				OnPaintSurface(...);
			}

			// This implementation is not fast enough, and providing the original pixel buffer
			// is needed, yet the internal `IBufferByteAccess` interface is not yet available in Uno.
			// Once it is, we can replace this implementation and provide the pinned array directly
			// to skia.
			using (var data = bitmap.PixelBuffer.AsStream())
			{
				data.Write(pixels, 0, pixels.Length);
				data.Flush();
			}

			bitmap.Invalidate();
		}
        }

See #15097 (reply in thread)

---

Before the SkiaVisual added, we can use the hack code to implemente the same functionality. The demo code: https://github.com/lindexi/lindexi_gd/tree/5db72c3d67f121becefb5c4e8a0eacd5099c4198/KefalurcilaybelJallbuderenajel

See #15097 (reply in thread)

[jeromelaban]

Thanks for the update. The hack you're suggesting is about exposing an API that is not meant to be exposed in the first place. We need a SkiaVisual in order for Uno.WinUI to expose an API that SkiaSharp and any other animplementation can use reliably.

[lindexi]

Good job!

[agneszitte]

@jeromelaban, @rafael-rosa-knowcode should @jhanvi03 or @Darsh0307 test the uno samples app for this new support?

[jeromelaban]

@agneszitte yes, the uno samples app contains a new sample for WPF and X11.

[ramezgerges]

@agneszitte @jeromelaban Not yet. The work is pretty much done but I removed it from #16621 because the PR was getting too big and we wanted to merge the GLCanvasElement work. I will open another PR for SKCanvasElement soon.

[agneszitte]

Thanks for the info @ramezgerges, let them know when it will be ready for QA when it will be done please