render/color: introduce COLOR_TRANSFORM_LUT_3X1D

This will be useful to apply LUTs applied via wlr_gamma_control_v1,
and to add wlr_color_transform support to wlr_output.

include/render/color.h

@@ -8,6 +8,7 @@
 enum wlr_color_transform_type {
 	COLOR_TRANSFORM_SRGB,
 	COLOR_TRANSFORM_LCMS2,
+	COLOR_TRANSFORM_LUT_3X1D,
 };
 
 struct wlr_color_transform {
@@ -20,6 +21,21 @@ struct wlr_color_transform {
 void wlr_color_transform_init(struct wlr_color_transform *tr,
 	enum wlr_color_transform_type type);
 
+/**
+ * The formula is approximated via three 1D look-up tables. The flat lut_3x1d
+ * array has a length of 3 * dim.
+ *
+ * The offset of a color value for a given channel and color index is:
+ *
+ *     offset = channel_index * dim + color_index
+ */
+struct wlr_color_transform_lut_3x1d {
+	struct wlr_color_transform base;
+
+	uint16_t *lut_3x1d;
+	size_t dim;
+};
+
 /**
  * Get a struct wlr_color_transform_lcms2 from a generic struct wlr_color_transform.
  * Asserts that the base type is COLOR_TRANSFORM_LCMS2.
@@ -35,6 +51,20 @@ void color_transform_lcms2_finish(struct wlr_color_transform_lcms2 *tr);
 void color_transform_lcms2_eval(struct wlr_color_transform_lcms2 *tr,
 	float out[static 3], const float in[static 3]);
 
+/**
+ * Get a struct wlr_color_transform_lut_3x1d from a generic
+ * struct wlr_color_transform. Asserts that the base type is
+ * COLOR_TRANSFORM_LUT_3X1D.
+ */
+struct wlr_color_transform_lut_3x1d *color_transform_lut_3x1d_from_base(
+	struct wlr_color_transform *tr);
+
+/**
+ * Evaluate a 3x1D LUT color transform for a given RGB triplet.
+ */
+void color_transform_lut_3x1d_eval(struct wlr_color_transform_lut_3x1d *tr,
+	float out[static 3], const float in[static 3]);
+
 /**
  * Obtain primaries values from a well-known primaries name.
  */

include/wlr/render/color.h

@@ -10,6 +10,7 @@
 #define WLR_RENDER_COLOR_H
 
 #include <stdbool.h>
+#include <stdint.h>
 #include <sys/types.h>
 
 /**
@@ -78,6 +79,13 @@ struct wlr_color_transform *wlr_color_transform_init_linear_to_icc(
  */
 struct wlr_color_transform *wlr_color_transform_init_srgb(void);
 
+/**
+ * Initialize a color transformation to apply three 1D look-up tables. dim
+ * is the number of elements in each individual LUT. Returns NULL on failure.
+ */
+struct wlr_color_transform *wlr_color_transform_init_lut_3x1d(size_t dim,
+	const uint16_t *r, const uint16_t *g, const uint16_t *b);
+
 /**
  * Increase the reference count of the color transform by 1.
  */

render/color.c

@@ -38,6 +38,28 @@ struct wlr_color_transform *wlr_color_transform_init_srgb(void) {
 	return tx;
 }
 
+struct wlr_color_transform *wlr_color_transform_init_lut_3x1d(size_t dim,
+		const uint16_t *r, const uint16_t *g, const uint16_t *b) {
+	uint16_t *lut_3x1d = malloc(3 * dim * sizeof(lut_3x1d[0]));
+	if (lut_3x1d == NULL) {
+		return NULL;
+	}
+
+	memcpy(&lut_3x1d[0 * dim], r, dim * sizeof(lut_3x1d[0]));
+	memcpy(&lut_3x1d[1 * dim], g, dim * sizeof(lut_3x1d[0]));
+	memcpy(&lut_3x1d[2 * dim], b, dim * sizeof(lut_3x1d[0]));
+
+	struct wlr_color_transform_lut_3x1d *tx = calloc(1, sizeof(*tx));
+	if (!tx) {
+		free(lut_3x1d);
+		return NULL;
+	}
+	wlr_color_transform_init(&tx->base, COLOR_TRANSFORM_LUT_3X1D);
+	tx->lut_3x1d = lut_3x1d;
+	tx->dim = dim;
+	return &tx->base;
+}
+
 static void color_transform_destroy(struct wlr_color_transform *tr) {
 	switch (tr->type) {
 	case COLOR_TRANSFORM_SRGB:
@@ -45,6 +67,10 @@ static void color_transform_destroy(struct wlr_color_transform *tr) {
 	case COLOR_TRANSFORM_LCMS2:
 		color_transform_lcms2_finish(color_transform_lcms2_from_base(tr));
 		break;
+	case COLOR_TRANSFORM_LUT_3X1D:;
+		struct wlr_color_transform_lut_3x1d *lut_3x1d = color_transform_lut_3x1d_from_base(tr);
+		free(lut_3x1d->lut_3x1d);
+		break;
 	}
 	wlr_addon_set_finish(&tr->addons);
 	free(tr);
@@ -66,6 +92,37 @@ void wlr_color_transform_unref(struct wlr_color_transform *tr) {
 	}
 }
 
+struct wlr_color_transform_lut_3x1d *color_transform_lut_3x1d_from_base(
+		struct wlr_color_transform *tr) {
+	assert(tr->type == COLOR_TRANSFORM_LUT_3X1D);
+	struct wlr_color_transform_lut_3x1d *lut_3x1d = wl_container_of(tr, lut_3x1d, base);
+	return lut_3x1d;
+}
+
+static float lut_1d_get(const uint16_t *lut, size_t len, size_t i) {
+	if (i > len) {
+		i = len - 1;
+	}
+	return (float) lut[i] / UINT16_MAX;
+}
+
+static float lut_1d_eval(const uint16_t *lut, size_t len, float x) {
+	double pos = x * (len - 1);
+	double int_part;
+	double frac_part = modf(pos, &int_part);
+	size_t i = (size_t) int_part;
+	double a = lut_1d_get(lut, len, i);
+	double b = lut_1d_get(lut, len, i + 1);
+	return a * (1 - frac_part) + b * frac_part;
+}
+
+void color_transform_lut_3x1d_eval(struct wlr_color_transform_lut_3x1d *tr,
+		float out[static 3], const float in[static 3]) {
+	for (size_t i = 0; i < 3; i++) {
+		out[i] = lut_1d_eval(&tr->lut_3x1d[tr->dim * i], tr->dim, in[i]);
+	}
+}
+
 void wlr_color_primaries_from_named(struct wlr_color_primaries *out,
 		enum wlr_color_named_primaries named) {
 	switch (named) {

render/vulkan/pass.c

@@ -838,7 +838,7 @@ void vk_color_transform_destroy(struct wlr_addon *addon) {
 }
 
 static bool create_3d_lut_image(struct wlr_vk_renderer *renderer,
-		struct wlr_color_transform_lcms2 *tr, size_t dim_len,
+		struct wlr_color_transform *tr, size_t dim_len,
 		VkImage *image, VkImageView *image_view,
 		VkDeviceMemory *memory, VkDescriptorSet *ds,
 		struct wlr_vk_descriptor_pool **ds_pool) {
@@ -851,6 +851,19 @@ static bool create_3d_lut_image(struct wlr_vk_renderer *renderer,
 	*ds = VK_NULL_HANDLE;
 	*ds_pool = NULL;
 
+	struct wlr_color_transform_lcms2 *tr_lcms2 = NULL;
+	struct wlr_color_transform_lut_3x1d *tr_lut_3x1d = NULL;
+	switch (tr->type) {
+	case COLOR_TRANSFORM_SRGB:
+		abort(); // unreachable
+	case COLOR_TRANSFORM_LCMS2:
+		tr_lcms2 = color_transform_lcms2_from_base(tr);
+		break;
+	case COLOR_TRANSFORM_LUT_3X1D:
+		tr_lut_3x1d = color_transform_lut_3x1d_from_base(tr);
+		break;
+	}
+
 	// R32G32B32 is not a required Vulkan format
 	// TODO: use it when available
 	VkFormat format = VK_FORMAT_R32G32B32A32_SFLOAT;
@@ -948,7 +961,11 @@ static bool create_3d_lut_image(struct wlr_vk_renderer *renderer,
 					b_index * sample_range,
 				};
 				float rgb_out[3];
-				color_transform_lcms2_eval(tr, rgb_out, rgb_in);
+				if (tr_lcms2 != NULL) {
+					color_transform_lcms2_eval(tr_lcms2, rgb_out, rgb_in);
+				} else {
+					color_transform_lut_3x1d_eval(tr_lut_3x1d, rgb_out, rgb_in);
+				}
 
 				dst[dst_offset] = rgb_out[0];
 				dst[dst_offset + 1] = rgb_out[1];
@@ -1018,10 +1035,9 @@ static struct wlr_vk_color_transform *vk_color_transform_create(
 		return NULL;
 	}
 
-	if (transform->type == COLOR_TRANSFORM_LCMS2) {
+	if (transform->type != COLOR_TRANSFORM_SRGB) {
 		vk_transform->lut_3d.dim = 33;
-		if (!create_3d_lut_image(renderer,
-				color_transform_lcms2_from_base(transform),
+		if (!create_3d_lut_image(renderer, transform,
 				vk_transform->lut_3d.dim,
 				&vk_transform->lut_3d.image,
 				&vk_transform->lut_3d.image_view,