Fix Metal stencil mismatch in mutable-image seed pass (#5103)#5106
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CN1MetalEnsureMutableTexture's seed pass (used when an existing UIImage's pixels need to be carried into a freshly-allocated mutable texture) built its render pass with only a colour attachment, then bound the TexturedRGBA pipeline -- which declares stencilAttachmentPixelFormat=Stencil8 since the polygon-clip work in #3921. Metal's validation layer aborts setRenderPipelineState: with "For stencil attachment, the renderPipelineState pixelFormat must be MTLPixelFormatInvalid, as no texture is set", crashing any app that lands on a screen whose first paint touches a seeded mutable image (e.g. gausianBlurImage, FontImage thumbnails). Allocate a throwaway Stencil8 texture for the pass mirroring the pattern already used in CN1MetalBeginMutableImageDraw. The seed draw never engages the stencil test, so loadAction=Clear / storeAction=DontCare is enough. The sibling clearPass above doesn't need the same treatment -- it never calls setRenderPipelineState:, so the validation rule isn't triggered. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Compared 122 screenshots: 122 matched. Benchmark Results
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Summary
setRenderPipelineState:withFor stencil attachment, the renderPipelineState pixelFormat must be MTLPixelFormatInvalid, as no texture is set.CN1MetalPipelineCache.mdeclaresstencilAttachmentPixelFormat = MTLPixelFormatStencil8(added with the polygon-clip stencil work in Clipping region not respected with non-90 degree rotations. #3921), so every render pass that binds one must attach a Stencil8 texture. The seed pass inCN1MetalEnsureMutableTexture(used to carry an existingUIImage's pixels —gausianBlurImage,FontImagethumbnails, etc. — into a freshly-allocated mutable target) was built with only a colour attachment but then bound the TexturedRGBA pipeline.CN1MetalBeginMutableImageDrawa few lines below. The seed draw never engages the stencil test, soloadAction=Clear/storeAction=DontCareis sufficient.The sibling
clearPassimmediately above the seed pass does not need the same fix — it never callssetRenderPipelineState:(it just clears the colour attachment and ends the encoder), so the validation rule is not triggered.Test plan
FontImage/gausianBlurImage-derived mutable image and confirm the app no longer crashes on the first form.🤖 Generated with Claude Code