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Interpolate MixOklab, Lerp and Gradient premultiplied, so a transparent end adds no color [minor] - #528
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…nt end adds no color [minor] Each color's channels now count in proportion to its alpha, as CSS Color 4 specifies, so Transparent.MixOklab(White, 0.5) is #FFFFFF80 rather than #63636380 and a fade-in from Transparent no longer passes through dark grey. A result with alpha 0 is transparent black. Opaque inputs mix as before. Fixes #526 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017vfJW5AXVu7aN3GSXPwGnx
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Fixes #526
What changed
MixOklabnow weights each color's L/a/b by its alpha, andLerpweights its linear R/G/B the same way. Both divide by the mixed alpha afterwards, as CSS Color 4 §12.3 specifies.Gradientgoes throughMixOklab, so it picks up the fix too.<remarks>now say interpolation is premultiplied. Colors are still stored with straight alpha.Results
Transparent.MixOklab(White, 0.5)#63636380#FFFFFF80Transparent.Lerp(White, 0.5)#BCBCBC80#FFFFFF80Transparent.Gradient(White, 5)#00000000 #22222240 #63636380 #AEAEAEBF #FFFFFF#00000000 #FFFFFF40 #FFFFFF80 #FFFFFFBF #FFFFFFRed.WithAlpha(0).MixOklab(Blue, 0.5)#8C53A280#0000FF80Tests
ColorGamutAndAlphaTests: mixing from Transparent in both directions, a fade-in gradient, an invisible end, two transparent ends, and an opaque control.Color.Operations.csmakes four of them fail. The opaque control passes both ways, which shows opaque mixes did not change.Semantics.Test: 1967 passed, 14 skipped, 0 failed.This changes behavior, so the commit is tagged
[minor].Generated by Claude Code