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28d99854a6
This reverts commit a7a25d3b57f2066798ef8cd43600588e4697c9cd and relands our reland https://github.com/flutter/engine/pull/17915. Additionally, we fixed the cull rect logic in `OpacityLayer::Preroll` which is the root cause of https://github.com/flutter/flutter/issues/56298. We've always had that root problem before but it did not trigger performance issues because we were using the OpacityLayer's `paint_bounds`, instead of its child's `paint_bounds` for preparing the layer raster cache. A correct handling of the cull rect should allow us to cull at any level. It also turns out that our ios32 (iPhone4s) performacne can regress a lot without snapping. My theory is that although the picture has a fractional top left corner, many drawing operations inside the picture have integral coordinations. In older hardwares, keeping those coordinates integral seems to be performance critical. To avoid flutter/flutter#41654, the snapping will still be disabled if the matrix has non-scale-translation transformations.
Flow
Flow is a simple compositor based on Skia that the Flutter engine uses to cache recoded paint commands and pixels generated from those recordings. Flow runs on the raster thread and uploads information to Skia.