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[web] Isolate SkwasmRenderer.pictureToImageSurface from rasterizer offscreenSurface - #192770
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harryterkelsen wants to merge 4 commits into
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…ce for issue-182476-skwasm
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On the web, a glTF texture went browser decode -> ui.Image -> Image.toByteData -> CPU mip chain -> texSubImage2D per level. That read-back runs on the framework's renderer, which on skwasm clips images above 5760² (flutter/flutter#182476) and races with frame rendering (flutter/flutter#192770), and the whole path blocks the main thread. createImageBitmap + texSubImage2D + generateMipmap never leaves the backend's WebGL context. Normal maps keep the CPU chain. Other backends return null and decode through dart:ui as before. Node.fromGlbBytes gains maxTextureSize, honoured on every backend.
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Description
In Skwasm,
SkwasmRenderer.pictureToImageSurfacedirectly aliased(rasterizer as OffscreenCanvasRasterizer).offscreenSurface. When asynchronousPicture.toImage()ortoByteData()calls ran concurrently with active view rendering (renderScene), viewport dimensions and rendering contexts contended, causing image exports to be corrupted or stomped by window dimensions.This PR decouples
pictureToImageSurfaceinSkwasmRendererto a dedicatedSurfacecreated viarasterizer.createPictureToImageSurface(), restoring architectural parity withCanvasKitRenderer. It also adds unit and adversarial lifecycle stress tests verifying isolation and reset semantics.Fixes part of #182476
Pre-launch Checklist
///).