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render: color: Add method to get matrix from encoding and range

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Signed-off-by: Andri Yngvason <andri@yngvason.is>
This commit is contained in:
Andri Yngvason 2026-05-18 15:45:19 +00:00
parent e8c03e9ce9
commit 99235f7142
2 changed files with 91 additions and 0 deletions
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3
include/render/color.h
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@ -108,4 +108,7 @@ void wlr_color_primaries_to_xyz(const struct wlr_color_primaries *primaries, flo
void wlr_color_transfer_function_get_default_luminance(enum wlr_color_transfer_function tf,
struct wlr_color_luminances *lum);
void wlr_color_rgb_to_ycbcr_matrix(enum wlr_color_encoding encoding,
enum wlr_color_range range, float matrix[static 16]);
#endif

88
render/color.c
View file

@ -5,6 +5,10 @@
#include "render/color.h"
#include "util/matrix.h"
struct luma_coefficients {
float kr, kb;
};
// See H.273 ColourPrimaries
static const struct wlr_color_primaries COLOR_PRIMARIES_SRGB = { // code point 1
@ -21,6 +25,12 @@ static const struct wlr_color_primaries COLOR_PRIMARIES_BT2020 = { // code point
.white = { 0.3127, 0.3290 },
};
static const struct luma_coefficients LUMA_COEFFICIENTS_BT709 = { 0.2126f, 0.0722f };
static const struct luma_coefficients LUMA_COEFFICIENTS_FCC = { 0.30f, 0.11f };
static const struct luma_coefficients LUMA_COEFFICIENTS_BT601 = { 0.299f, 0.114f };
static const struct luma_coefficients LUMA_COEFFICIENTS_SMPTE240 = { 0.212f, 0.087f };
static const struct luma_coefficients LUMA_COEFFICIENTS_BT2020 = { 0.2627f, 0.0593f };
void wlr_color_transform_init(struct wlr_color_transform *tr, enum wlr_color_transform_type type) {
*tr = (struct wlr_color_transform){
.type = type,
@ -431,3 +441,81 @@ void wlr_color_transfer_function_get_default_luminance(enum wlr_color_transfer_f
break;
}
}
static const struct luma_coefficients *luma_coefficients_from_encoding(enum wlr_color_encoding encoding) {
switch (encoding) {
case WLR_COLOR_ENCODING_NONE:
case WLR_COLOR_ENCODING_IDENTITY:
return NULL;
case WLR_COLOR_ENCODING_BT709:
return &LUMA_COEFFICIENTS_BT709;
case WLR_COLOR_ENCODING_FCC:
return &LUMA_COEFFICIENTS_FCC;
case WLR_COLOR_ENCODING_BT601:
return &LUMA_COEFFICIENTS_BT601;
case WLR_COLOR_ENCODING_SMPTE240:
return &LUMA_COEFFICIENTS_SMPTE240;
case WLR_COLOR_ENCODING_BT2020:
case WLR_COLOR_ENCODING_BT2020_CL:
return &LUMA_COEFFICIENTS_BT2020;
case WLR_COLOR_ENCODING_ICTCP:
return NULL;
}
return NULL;
}
// https://en.wikipedia.org/w/index.php?title=YCbCr&oldid=1350695871#RGB_conversion
static void rgb_to_ypbpr(const struct luma_coefficients *coeffs, float out[static 16]) {
float kr = coeffs->kr;
float kb = coeffs->kb;
float kg = 1.0f - kr - kb;
float pb_r = -kr / (2.0f * (1.0f - kb));
float pb_g = -kg / (2.0f * (1.0f - kb));
float pr_g = -kg / (2.0f * (1.0f - kr));
float pr_b = -kb / (2.0f * (1.0f - kr));
// This is column major, but the matrix is row major on wikipedia.
float m[16] = {
kr, pb_r, 0.5f, 0.0f,
kg, pb_g, pr_g, 0.0f,
kb, 0.5f, pr_b, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f,
};
memcpy(out, m, sizeof(m));
}
static void apply_color_range(enum wlr_color_range range, float matrix[static 16]) {
float y_scale = 1.0f, y_offset = 0.0f;
float c_scale = 1.0f, c_offset = 0.5f;
if (range == WLR_COLOR_RANGE_LIMITED) {
y_scale = 219.0f / 255.0f;
y_offset = 16.0f / 255.0f;
c_scale = 224.0f / 255.0f;
c_offset = 128.0f / 255.0f;
}
for (int col = 0; col < 4; col++) {
matrix[col * 4 + 0] *= y_scale;
matrix[col * 4 + 1] *= c_scale;
matrix[col * 4 + 2] *= c_scale;
}
matrix[12] = y_offset;
matrix[13] = c_offset;
matrix[14] = c_offset;
}
void wlr_color_rgb_to_ycbcr_matrix(enum wlr_color_encoding encoding,
enum wlr_color_range range, float matrix[static 16]) {
const struct luma_coefficients *coeffs = luma_coefficients_from_encoding(encoding);
if (coeffs == NULL) {
static const float identity[16] = {
1.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 0.0f,
0.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 1.0f,
};
memcpy(matrix, identity, sizeof(identity));
return;
}
rgb_to_ypbpr(coeffs, matrix);
apply_color_range(range, matrix);
}