render/color: introduce wlr_color_transform

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

include/meson.build

@@ -20,6 +20,9 @@ endif
 if not features.get('vulkan-renderer')
 	exclude_files += 'render/vulkan.h'
 endif
+if not features.get('color-management')
+	exclude_files += 'render/color.h'
+endif
 if not features.get('session')
 	exclude_files += 'backend/session.h'
 endif

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

include/wlr/config.h.in

@@ -14,4 +14,6 @@
 
 #mesondefine WLR_HAS_SESSION
 
+#mesondefine WLR_HAS_COLOR_MANAGEMENT
+
 #endif

include/wlr/render/color.h

@@ -0,0 +1,55 @@
+/*
+ * This an unstable interface of wlroots. No guarantees are made regarding the
+ * future consistency of this API.
+ */
+#ifndef WLR_USE_UNSTABLE
+#error "Add -DWLR_USE_UNSTABLE to enable unstable wlroots features"
+#endif
+
+#ifndef WLR_RENDER_COLOR_H
+#define WLR_RENDER_COLOR_H
+
+#include <stdbool.h>
+#include <sys/types.h>
+
+/**
+ * A color transformation formula, which maps a linear color space with
+ * sRGB primaries to an output color space.
+ *
+ * For ease of use, this type is heap allocated and reference counted.
+ * Use wlr_color_transform_ref()/wlr_color_transform_unref(). The initial reference
+ * count after creation is 1.
+ *
+ * Color transforms are immutable; their type/parameters should not be changed,
+ * and this API provides no functions to modify them after creation.
+ *
+ * This formula may be implemented using a 3d look-up table, or some other
+ * means.
+ */
+struct wlr_color_transform;
+
+/**
+ * Initialize a color transformation to convert linear
+ * (with sRGB(?) primaries) to an ICC profile. Returns NULL on failure.
+ */
+struct wlr_color_transform *wlr_color_transform_init_linear_to_icc(
+	const void *data, size_t size);
+
+/**
+ * Initialize a color transformation to apply sRGB encoding.
+ * Returns NULL on failure.
+ */
+struct wlr_color_transform *wlr_color_transform_init_srgb(void);
+
+/**
+ * Increase the reference count of the color transform by 1.
+ */
+void wlr_color_transform_ref(struct wlr_color_transform *tr);
+
+/**
+ * Reduce the reference count of the color transform by 1; freeing it and
+ * all associated resources when the reference count hits zero.
+ */
+void wlr_color_transform_unref(struct wlr_color_transform *tr);
+
+#endif