Let AdjustForContrast darken on mid-tone backgrounds [patch] - #292
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AdjustForContrast chose its direction with a 0.5 luminance threshold, but white and black give equal contrast near luminance 0.179. On any background between those two it searched only the lightening direction, which cannot reach AA, and returned the failing colour unchanged. Search first toward the extreme with more contrast headroom, and fall back to the other direction before giving up. Fixes #279 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01PKmokmgnpkeYgp439Qbthh
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This was referenced Sep 28, 2026
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Fixes #279
What was wrong
Color.AdjustForContrastpicked its search direction withbackground.RelativeLuminance < 0.5. White and black actually give equal contrast near luminance 0.179. On any background between 0.18 and 0.5, the method only searched toward white. That direction cannot reach AA there (or large-text AA above about 0.30), so the method returned the failing foreground unchanged.Change
1.05/(L+0.05) >= (L+0.05)/0.05).Search(goLighter)function.Tests
AdjustForContrast_DarkensOnMidToneBackgrounduses the issue's example: background sRGB 0.58 grey (L ≈ 0.296), AA.AdjustForContrast_ReachesLargeTextAAOnUpperMidToneBackground: background sRGB 0.7 grey (L ≈ 0.45), large-text AA.AdjustForContrast_LightensOnDarkBackgroundis a guard that dark backgrounds still lighten.The first two fail on
mainand pass with this change. The fullSemantics.Testsuite passes: 1336 passed, 8 skipped.🤖 Generated with Claude Code
https://claude.ai/code/session_01PKmokmgnpkeYgp439Qbthh
Generated by Claude Code