Added SKImage field to WriteableBitmapImpl for improved drawing performance

[AngryCarrot789]

What does the pull request do?

It adds two fields, SKBitmap and SKPixmap, which are created in each constructor. The SKImage is used in the Draw() method for improved performance, since in the original implementation, DrawBitmap() allocates a new SKImage each time (which requires copying the entire bitmap according to the C++ implementation when the bitmap is mutable, which it always is in this class).

I also added optimisation to use DrawImage with coordinates instead of Rect, since sk_canvas_draw_image_rect has some sort of overhead: #2849 (comment)

What is the updated/expected behavior with this PR?

The performance of drawing a WriteableBitmap should be improved, especially for large images (4K+). I've noticed a subtle performance increase when drawing a 1920x1080 bitmap.

[avaloniaui-bot]

You can test this PR using the following package version. 11.3.999-cibuild0053761-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

[AngryCarrot789]

This doesn't seem to work when starting the app with Win32CompositionMode.DirectComposition in the Win32PlatformOptions

[timunie]

We can't rely on Skia by default. So the idea isn't bad at all but we need a way to figure out if chaching is okay or not.

[kekekeks]

Context: there previously was SKCanvas::drawBitmap, but it apparently got removed around 2021 and SkiaSharp have silently added a shim. We've previously relied on Skia caching gpu bitmap data and NotifyPixelChanged call for invalidation.

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The way you are trying to use SKImage with SKPixmap is strictly invalid. The docs explicitly specify that the underlying pixmap should be unchanged until SKImage is destroyed.

For it to work properly we need to manually re-create an SKImage from SKBitmap (so it would make a snapshot) when drawing if pixel data was changed since the last time.