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WaylandBackend: fix overflow when forwarding mastering primaries - #2525
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matte-schwartz merged 1 commit intoOct 30, 2026
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Rescaling the HDR10 mastering display primaries multiplies a 1/50000-unit value by 1'000'000 in 32 bits, which overflows for any realistic chromaticity. The parent compositor receives garbage, often negative, primaries (BT.2020 green arrives as -1798, 23905 instead of 170000, 797000), and KWin shows HDR10 games clipped to SDR. The ratio between the infoframe unit (1/50000) and the protocol unit (1/1000000) is exactly 20, so multiply by that instead of widening the intermediate. This is exact and cannot overflow. Closes: ValveSoftware#2524
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Nice hdr works fine with this! Thank you. |
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Rescaling the HDR10 mastering display primaries multiplies a 1/50000-unit value by 1'000'000 in 32 bits, which overflows for any realistic chromaticity. The parent compositor receives garbage, often negative, primaries (BT.2020 green arrives as -1798, 23905 instead of 170000, 797000), and KWin shows HDR10 games clipped to SDR.
The ratio between the infoframe unit (1/50000) and the protocol unit (1/1000000) is exactly 20, so multiply by that instead of widening the intermediate. This is exact and cannot overflow.
Closes: #2524