render/color: add wlr_color_primaries_to_xyz()

include/render/color.h

@@ -45,4 +45,9 @@ struct wlr_color_transform_lut3d {
 struct wlr_color_transform_lut3d *wlr_color_transform_lut3d_from_base(
 	struct wlr_color_transform *tr);
 
+/**
+ * Compute the matrix to convert RGB color values to CIE 1931 XYZ.
+ */
+void wlr_color_primaries_to_xyz(const struct wlr_color_primaries *primaries, float matrix[static 9]);
+
 #endif

include/wlr/render/color.h

@@ -12,6 +12,20 @@
 #include <stdbool.h>
 #include <sys/types.h>
 
+/**
+ * CIE 1931 xy chromaticity coordinates.
+ */
+struct wlr_color_cie1931_xy {
+	float x, y;
+};
+
+/**
+ * Color primaries and white point describing a color volume.
+ */
+struct wlr_color_primaries {
+	struct wlr_color_cie1931_xy red, green, blue, white;
+};
+
 /**
  * A color transformation formula, which maps a linear color space with
  * sRGB primaries to an output color space.

render/color.c

@@ -1,7 +1,9 @@
 #include <assert.h>
 #include <stdlib.h>
+#include <string.h>
 #include <wlr/render/color.h>
 #include "render/color.h"
+#include "util/matrix.h"
 
 struct wlr_color_transform *wlr_color_transform_init_srgb(void) {
 	struct wlr_color_transform *tx = calloc(1, sizeof(struct wlr_color_transform));
@@ -50,3 +52,50 @@ struct wlr_color_transform_lut3d *wlr_color_transform_lut3d_from_base(
 	struct wlr_color_transform_lut3d *lut3d = wl_container_of(tr, lut3d, base);
 	return lut3d;
 }
+
+static void multiply_matrix_vector(float out[static 3], float m[static 9], float v[static 3]) {
+	float result[3] = {
+		m[0] * v[0] + m[1] * v[1] + m[2] * v[2],
+		m[3] * v[0] + m[4] * v[1] + m[5] * v[2],
+		m[6] * v[0] + m[7] * v[1] + m[8] * v[2],
+	};
+	memcpy(out, result, sizeof(result));
+}
+
+static void xy_to_xyz(float out[static 3], struct wlr_color_cie1931_xy src) {
+	if (src.y == 0) {
+		out[0] = out[1] = out[2] = 0;
+		return;
+	}
+
+	out[0] = src.x / src.y;
+	out[1] = 1;
+	out[2] = (1 - src.x - src.y) / src.y;
+}
+
+void wlr_color_primaries_to_xyz(const struct wlr_color_primaries *primaries, float matrix[static 9]) {
+	// See: http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html
+
+	float r[3], g[3], b[3], w[3];
+	xy_to_xyz(r, primaries->red);
+	xy_to_xyz(g, primaries->green);
+	xy_to_xyz(b, primaries->blue);
+	xy_to_xyz(w, primaries->white);
+
+	float xyz_matrix[9] = {
+		r[0], g[0], b[0],
+		r[1], g[1], b[1],
+		r[2], g[2], b[2],
+	};
+	matrix_invert(xyz_matrix, xyz_matrix);
+
+	float S[3];
+	multiply_matrix_vector(S, xyz_matrix, w);
+
+	float result[] = {
+		S[0] * r[0], S[1] * g[0], S[2] * b[0],
+		S[0] * r[1], S[1] * g[1], S[2] * b[1],
+		S[0] * r[2], S[1] * g[2], S[2] * b[2],
+	};
+	memcpy(matrix, result, sizeof(result));
+}