feImage: skip pixels outside targetRect in filter pipeline#24
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When feImage has a targetRect smaller than the output region, the bilinear interpolation loop previously wrote into pixels outside the target rectangle, producing bleed artifacts at the edges. Add a pixel-center bounds check before sampling so that only pixels whose centers fall inside the targetRect are populated. Pixels outside the target remain transparent. Found during donner's SVG <filter> integration testing.
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Summary
When
feImagehas atargetRectsmaller than the output region, the bilinear interpolation loop inexecuteFilterGraphpreviously wrote into pixels whose centers fall outside the target rectangle, producing bleed artifacts at the edges.This PR adds a pixel-center bounds check before sampling so only pixels whose centers fall inside
targetRectare populated. Pixels outside the target remain transparent, matching the SVG spec expectation.The fix was originally developed in donner PR #444 ("Implement full SVG support for TinySkia and Skia backends") where donner vendors this library as a git subtree. This PR brings the fix back upstream as part of syncing the donner subtree with upstream
main.Context
The donner subtree had drifted somewhat from upstream. After running
git subtree pullinto donner's worktree, the only substantive outgoing delta against upstreammainwas thisFilterGraph.cppchange (other deltas were local Bazel/zlib path adaptations and cosmetic whitespace).Test plan
feImagewith a partialtargetRect, if one is not already coveredbazel build //donner/svg/renderer/...(passing) and fullbazel build //donner/...(passing)