feat(converter): add Bt709LinearToBt2020Pq color space variant#15
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feat(converter): add Bt709LinearToBt2020Pq color space variant#15lutyjj wants to merge 1 commit into
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Adds a fourth ColorSpace variant for scRGB-linear (BT.709 primaries, linear-light) FP16 input converted to BT.2020+PQ output. Distinct from SrgbToBt2020Pq in that the sRGB EOTF is skipped — scRGB is already linear, and frequently carries values > 1.0 representing HDR highlights beyond SDR white. Routing those through srgb_to_linear() would clamp to [0, 1] and crush exactly the range that needs to survive encode. The remaining math matches SrgbToBt2020Pq: BT.709→BT.2020 gamut mapping in linear light, scale by sdr_reference_white_nits / 10000, then PQ OETF. Reference white differs by source convention — 203 nits for ITU-R BT.2408 SDR-in-HDR (existing default) versus 80 nits for the scRGB spec (IEC 61966-2-2, 1.0 == 80 cd/m²). DXVK's dxvk_color_space.glsl splits these the same way. Required for HDR streaming of DX12 games running under VKD3D-Proton: their swapchains negotiate DXGI_COLOR_SPACE_RGB_FULL_G10_NONE_P709 → VK_COLOR_SPACE_EXTENDED_SRGB_LINEAR_EXT (CryEngine titles, Kingdom Come: Deliverance II, Witcher 3 Next-Gen) and submit FP16 linear BT.709 buffers. Without this variant there is no correct encode path for that input: SrgbToBt2020Pq clamps the highlights, Bt2020 passthrough skips the PQ encode entirely. Also adds a runtime setter for sdr_reference_white_nits so callers can flip between 80 and 203 per-frame without rebuilding the converter, mirroring set_color_space / set_full_range — needed when the upstream compositor's color space changes at runtime (e.g. menu ↔ game toggling between sRGB and scRGB). Purely additive: existing Bt709 / Bt2020 / SrgbToBt2020Pq paths are unchanged.
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Adds a fourth ColorSpace variant for scRGB-linear (BT.709 primaries, linear-light) FP16 input converted to BT.2020+PQ output. Distinct from SrgbToBt2020Pq in that the sRGB EOTF is skipped — scRGB is already linear, and frequently carries values > 1.0 representing HDR highlights beyond SDR white. Routing those through srgb_to_linear() would clamp to [0, 1] and crush exactly the range that needs to survive encode.
The remaining math matches SrgbToBt2020Pq: BT.709→BT.2020 gamut mapping in linear light, scale by sdr_reference_white_nits / 10000, then PQ OETF. Reference white differs by source convention — 203 nits for ITU-R BT.2408 SDR-in-HDR (existing default) versus 80 nits for the scRGB spec (IEC 61966-2-2, 1.0 == 80 cd/m²). DXVK's dxvk_color_space.glsl splits these the same way.
Required for HDR streaming of DX12 games running under VKD3D-Proton: their swapchains negotiate
DXGI_COLOR_SPACE_RGB_FULL_G10_NONE_P709 → VK_COLOR_SPACE_EXTENDED_SRGB_LINEAR_EXT (CryEngine titles, Kingdom Come: Deliverance II, Witcher 3 Next-Gen) and submit FP16 linear BT.709 buffers. Without this variant there is no correct encode path for that input.
Also adds a runtime setter for sdr_reference_white_nits so callers can flip between 80 and 203 per-frame without rebuilding the converter, mirroring set_color_space / set_full_range — needed when the upstream compositor's color space changes at runtime (e.g. menu ↔ game toggling between sRGB and scRGB, had this in KCD2 - in main menu, when there's no mouse HDR was working fine, but once you start moving the cursor - bam, HDR is gone).
Purely additive, existing Bt709 / Bt2020 / SrgbToBt2020Pq paths are unchanged.
Continuation of hgaiser/moonshine#87.