render/color: introduce wlr_color_transform

Co-authored-by: Manuel Stoeckl <code@mstoeckl.com>

include/render/color.h

@@ -0,0 +1,39 @@
+#ifndef RENDER_COLOR_H
+#define RENDER_COLOR_H
+
+#include <stdint.h>
+#include <wlr/util/addon.h>
+
+/**
+ * The formula is approximated via a 3D look-up table. A 3D LUT is a
+ * three-dimensional array where each element is an RGB triplet. The flat lut_3d
+ * array has a length of dim_len³.
+ *
+ * Color channel values in the range [0.0, 1.0] are mapped linearly to
+ * 3D LUT indices such that 0.0 maps exactly to the first element and 1.0 maps
+ * exactly to the last element in each dimension.
+ *
+ * The offset of the RGB triplet given red, green and blue indices r_index,
+ * g_index and b_index is:
+ *
+ *     offset = 3 * (r_index + dim_len * g_index + dim_len * dim_len * b_index)
+ */
+struct wlr_color_transform_lut3d {
+	float *lut_3d;
+	size_t dim_len;
+};
+
+enum wlr_color_transform_type {
+	COLOR_TRANSFORM_SRGB,
+	COLOR_TRANSFORM_LUT_3D,
+};
+
+struct wlr_color_transform {
+	int ref_count;
+	struct wlr_addon_set addons; // per-renderer helper state
+
+	enum wlr_color_transform_type type;
+	struct wlr_color_transform_lut3d lut3d;
+};
+
+#endif