docs: document ImageMagick path fill rendering bug#234
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ImageMagick's GetFillAlpha function (MagickCore/draw.c) has two interacting bugs that can produce single white pixel artifacts in filled regions: 1. The winding number calculation uses `x <= bounds.x1` instead of `x < bounds.x1`, causing pixels at an edge's leftmost x to be incorrectly classified as outside the polygon. 2. DestroyEdge does not decrement the loop counter after removing an edge, causing the next edge in the array to be skipped in the distance phase. Neither canvas padding nor post-processing can reliably fix this. Users should use SvgImageBackEnd or GDLibRenderer instead. Closes #195 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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ImageMagick's GetFillAlpha function (MagickCore/draw.c) has two interacting bugs that can produce single white pixel artifacts in filled regions:
The winding number calculation uses
x <= bounds.x1instead ofx < bounds.x1, causing pixels at an edge's leftmost x to be incorrectly classified as outside the polygon.DestroyEdge does not decrement the loop counter after removing an edge, causing the next edge in the array to be skipped in the distance phase.
Neither canvas padding nor post-processing can reliably fix this. Users should use SvgImageBackEnd or GDLibRenderer instead.
Closes #195