fix: use correct 5-bit to 8-bit color conversion formula#44
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eddmann merged 2 commits intoNov 11, 2025
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Changes the CGB color conversion from simple multiplication/division to the bit-perfect formula specified in cgb-acid2 test documentation: (r << 3) | (r >> 2) This ensures accurate color reproduction that matches hardware behavior and passes color accuracy requirements for test ROMs. Before: RGB555(13,23,31) -> RGB888(106,189,255) ❌ After: RGB555(13,23,31) -> RGB888(107,189,255) ✅ Improves cgb-acid2 output accuracy from 83.36% to proper color values. Note: cgb-acid2 still shows 84.96% similarity to reference due to separate PPU rendering issues (yellow/black pixels rendering as white in mouth/nose regions). Color conversion is now correct. Affects: src/Ppu/Color.php:56-62
Documents the color conversion fix and remaining PPU rendering issues: Fixed (84.96% similarity achieved): - ✅ 5-bit to 8-bit color conversion now bit-perfect - ✅ Colors render correctly per CGB hardware spec Remaining Issues (15.04% difference from reference): - Yellow/black pixels rendering as white (3,376 pixels) - Primarily affecting mouth (1,306px) and nose (238px) regions - Root causes likely: palette selection, priority handling, or VRAM banking Analysis includes: - Detailed pixel difference breakdown - Color substitution patterns - Affected regions mapped to test features - Recommended investigation steps - Reference links and success criteria This provides a roadmap for achieving 100% cgb-acid2 compliance.
eddmann
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claude/debug-acid2-colors-011CV2mmi5aDpXphvxm1bZ3A
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Changes the CGB color conversion from simple multiplication/division
to the bit-perfect formula specified in cgb-acid2 test documentation:
(r << 3) | (r >> 2)
This ensures accurate color reproduction that matches hardware behavior
and passes color accuracy requirements for test ROMs.
Before: RGB555(13,23,31) -> RGB888(106,189,255) ❌
After: RGB555(13,23,31) -> RGB888(107,189,255) ✅
Improves cgb-acid2 output accuracy from 83.36% to proper color values.
Note: cgb-acid2 still shows 84.96% similarity to reference due to
separate PPU rendering issues (yellow/black pixels rendering as white
in mouth/nose regions). Color conversion is now correct.
Affects: src/Ppu/Color.php:56-62