[canvaskit] Enable CanvasKit to compute tight SkPicture bounds

[harryterkelsen]

Passes the computeBounds bool argument to PictureRecorder.beginRecording. This will allow us to get tight bounds of the draw commands in the Picture, which enables us to optimize away Pictures which don't paint anything, or optimize away overlays that don't overlap with Platform views.

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[yjbanov]

LGTM but an extra LGTM from @eyebrowsoffire would be nice, especially from the WasmGC point of view.

[eyebrowsoffire]

One other bounds calculation gotcha I had to deal with when I was implementing Skwasm was the ImageFilterEngineLayer. The filter itself might actually change the bounds of the content it is filtering. Skia has an API called filterBounds on their image filters that takes an input cull rect and gives the output cull rect. They do this on the native side as well. See https://github.com/flutter/engine/blame/40a8732a5de0e63f2903bf0e565383f9671ce93c/lib/web_ui/lib/src/engine/skwasm/skwasm_impl/layers.dart#L164 for how I did this in Skwasm, I think you'll need a similar adjustment on the CanvasKit side (or else it cuts off some of the content of blurred images, for example)

[eyebrowsoffire]

I actually made this abstract class that you might want to conform to here: https://github.com/flutter/engine/blame/893ab3bf7bb9cf104846ec50b79baf4864089253/lib/web_ui/lib/src/engine/scene_painting.dart#L15C3-L15C3

I actually wrote Skwasm's scene builder in an agnostic way where it could theoretically be reused for any renderer that implements the normal dart:ui interfaces plus a few odds and ends that aren't exposed (such as this cullRect function). It might be interesting to see if CanvasKit could be migrated to that scene builder and do some perf measurements at some point, I think it does a little less work in some cases than the CanvasKit one (although it doesn't support platform views yet, so we wouldn't want to switch over to that until the platform views are implemented).

I also think a getter for cullRect makes more sense than a function, but up to you.

[harryterkelsen]

Thanks! I'm getting started on the filterBounds CanvasKit change

[harryterkelsen]

https://skia-review.googlesource.com/c/skia/+/721299 is out for review

[harryterkelsen]

Done.

[harryterkelsen]

Filed flutter/flutter#130453 to track the work of adjusting the image filter bounds using filterBounds

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