fix(hex2rgb): preserve full alpha precision when parsing hex colors - #392
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fix(hex2rgb): preserve full alpha precision when parsing hex colors#392spokodev wants to merge 2 commits into
spokodev wants to merge 2 commits into
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hex2rgb rounded the parsed alpha of #rrggbbaa / #rgba colors to two
decimals, so alpha bytes did not round-trip and the (exactly parsed)
RGB channels disagreed with alpha:
chroma('#ff000088').alpha() // 0.53, exact is 136/255 = 0.5333…
chroma('#ff000088').hex() // '#ff000087', not '#ff000088'
Parse alpha as the exact byte / 255, matching the RGB channels. This also
brings the APCA contrast of colors with alpha in line with the APCA demo
values the test already noted (36.7, -68.6), so that todo is resolved.
Updated the hex2rgb / alpha / contrast fixtures that encoded the rounded
values; full suite green (2519).
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When parsing
#rrggbbaa/#rgbacolors,hex2rgbrounds the alpha channel to two decimals:The RGB channels are parsed exactly (
& 0xff), so only alpha is degraded. As a result alpha bytes do not round-trip and the channels disagree:136 of 256 alpha bytes fail to round-trip. CSS Color 4 §5.2 defines the hex alpha as
aa / 255exactly.The fix parses alpha as the exact
(u & 0xff) / 0xff, matching how the RGB channels are handled. As a side effect it also aligns the APCA contrast of colors with alpha with the values the contrast test already noted in comments (// 36.7,// -68.6), so thattodois removed. Thehex2rgb,alpha, andcontrastfixtures that encoded the rounded values are updated. Full suite passes (2519).