slang-shaders/hdr/shaders/include/hdr10.h

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#define kMaxNitsFor2084 10000.0f
const mat3 k709_to_2020 = mat3 (
0.6274040f, 0.3292820f, 0.0433136f,
0.0690970f, 0.9195400f, 0.0113612f,
0.0163916f, 0.0880132f, 0.8955950f);
/* START Converted from (Copyright (c) Microsoft Corporation - Licensed under the MIT License.) https://github.com/microsoft/Xbox-ATG-Samples/tree/master/Kits/ATGTK/HDR */
const mat3 kExpanded709_to_2020 = mat3 (
0.6274040f, 0.3292820f, 0.0433136f,
0.0457456f, 0.941777f, 0.0124772f,
-0.00121055f, 0.0176041f, 0.983607f);
const mat3 k2020Gamuts[2] = { k709_to_2020, kExpanded709_to_2020 };
float LinearToST2084_1(const float channel)
{
float ST2084 = pow((0.8359375f + 18.8515625f * pow(abs(channel), 0.1593017578f)) / (1.0f + 18.6875f * pow(abs(channel), 0.1593017578f)), 78.84375f);
return ST2084; /* Don't clamp between [0..1], so we can still perform operations on scene values higher than 10,000 nits */
}
vec3 LinearToST2084(const vec3 colour)
{
return vec3(LinearToST2084_1(colour.r), LinearToST2084_1(colour.g), LinearToST2084_1(colour.b));
}
/* END Converted from (Copyright (c) Microsoft Corporation - Licensed under the MIT License.) https://github.com/microsoft/Xbox-ATG-Samples/tree/master/Kits/ATGTK/HDR */
/* Convert into HDR10 */
vec3 Hdr10(const vec3 hdr_linear, float paper_white_nits, float expand_gamut)
{
const vec3 rec2020 = hdr_linear * k2020Gamuts[uint(expand_gamut)];
const vec3 linearColour = rec2020 * (paper_white_nits / kMaxNitsFor2084);
vec3 hdr10 = LinearToST2084(linearColour);
return hdr10;
}