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Fix degeneracy check for resize transforms - #3157
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Use exact zero determinant checks in `TransformUtilities.IsDegenerate` for `Matrix3x2` and `Matrix4x4` instead of epsilon-based near-zero detection, preventing valid transforms from being treated as degenerate during extreme downscales. Added a regression test for issue #3156 to verify resizing large square images (1024/2048) to 1x1 succeeds and preserves the expected pixel.
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Pull request overview
Fixes a regression where very small-but-valid resize transforms (eg 2048×2048 → 1×1) were incorrectly treated as degenerate, causing DegenerateTransformException during resize operations.
Changes:
- Updated
TransformUtilities.IsDegenerateforMatrix3x2andMatrix4x4to treat matrices as degenerate only when the determinant is exactly zero (instead of near-zero via epsilon). - Removed the now-unused epsilon-based
IsZero(float)helper fromTransformUtilities. - Added a regression test covering resizing large square images (1024/2048) down to a single pixel and validating the resulting pixel value.
Reviewed changes
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| File | Description |
|---|---|
| tests/ImageSharp.Tests/Processing/Processors/Transforms/ResizeTests.cs | Adds a regression test ensuring large-square → 1×1 resize succeeds and preserves expected output. |
| src/ImageSharp/Processing/Processors/Transforms/TransformUtilities.cs | Adjusts degeneracy detection to avoid false positives for extreme downscales. |
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Prerequisites
Description
Fixes #3156
Use exact zero determinant checks in
TransformUtilities.IsDegenerateforMatrix3x2andMatrix4x4instead of epsilon-based near-zero detection, preventing valid transforms from being treated as degenerate during extreme downscales. Added a regression test for issue #3156 to verify resizing large square images (1024/2048) to 1x1 succeeds and preserves the expected pixel.