render/color: Invert ownership model of color_transform types.

Color transform can have multiple types and these different types
want to store different metadata. We previously stored this metadata
directly on wlr_color_transform even for transforms that don't use it.

Instead, let's take the prior art from wlr_scene where each scene node
is built on a base node. Notice how wlr_color_transform_lut3d now has
a `struct wlr_color_transform base`. This is advantageous in multiple
ways:

1. We don't allocate memory for metadata that will never be used.
2. This is more type safe: Compositors can pass around a
struct wlr_color_transform_lut3d if they know they only want to use a
3d_lut.
3. This is more scalable. As we add more transform types, we don't have
to keep growing a monolithic struct.

include/render/color.h

@@ -4,6 +4,18 @@
 #include <stdint.h>
 #include <wlr/util/addon.h>
 
+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;
+};
+
 /**
  * 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
@@ -19,21 +31,17 @@
  *     offset = 3 * (r_index + dim_len * g_index + dim_len * dim_len * b_index)
  */
 struct wlr_color_transform_lut3d {
+	struct wlr_color_transform base;
+
 	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;
-};
+/**
+ * Gets a wlr_color_transform_lut3d from a generic wlr_color_transform.
+ * Asserts that the base type is COLOR_TRANSFORM_LUT_3D
+ */
+struct wlr_color_transform_lut3d *wlr_color_transform_lut3d_from_base(
+	struct wlr_color_transform *tr);
 
 #endif

render/color.c

@@ -15,7 +15,15 @@ struct wlr_color_transform *wlr_color_transform_init_srgb(void) {
 }
 
 static void color_transform_destroy(struct wlr_color_transform *tr) {
-	free(tr->lut3d.lut_3d);
+	switch (tr->type) {
+	case COLOR_TRANSFORM_SRGB:
+		break;
+	case COLOR_TRANSFORM_LUT_3D:;
+		struct wlr_color_transform_lut3d *lut3d =
+			wlr_color_transform_lut3d_from_base(tr);
+		free(lut3d->lut_3d);
+		break;
+	}
 	wlr_addon_set_finish(&tr->addons);
 	free(tr);
 }
@@ -35,3 +43,10 @@ void wlr_color_transform_unref(struct wlr_color_transform *tr) {
 		color_transform_destroy(tr);
 	}
 }
+
+struct wlr_color_transform_lut3d *wlr_color_transform_lut3d_from_base(
+		struct wlr_color_transform *tr) {
+	assert(tr->type == COLOR_TRANSFORM_LUT_3D);
+	struct wlr_color_transform_lut3d *lut3d = wl_container_of(tr, lut3d, base);
+	return lut3d;
+}

render/color_lcms2.c

@@ -18,7 +18,7 @@ static void handle_lcms_error(cmsContext ctx, cmsUInt32Number code, const char *
 
 struct wlr_color_transform *wlr_color_transform_init_linear_to_icc(
 		const void *data, size_t size) {
-	struct wlr_color_transform *tx = NULL;
+	struct wlr_color_transform_lut3d *tx = NULL;
 
 	cmsContext ctx = cmsCreateContext(NULL, NULL);
 	if (ctx == NULL) {
@@ -95,15 +95,15 @@ struct wlr_color_transform *wlr_color_transform_init_linear_to_icc(
 		}
 	}
 
-	tx = calloc(1, sizeof(struct wlr_color_transform));
+	tx = calloc(1, sizeof(struct wlr_color_transform_lut3d));
 	if (!tx) {
 		goto out_lcms_tr;
 	}
-	tx->type = COLOR_TRANSFORM_LUT_3D;
-	tx->lut3d.dim_len = dim_len;
-	tx->lut3d.lut_3d = lut_3d;
-	tx->ref_count = 1;
-	wlr_addon_set_init(&tx->addons);
+	tx->base.type = COLOR_TRANSFORM_LUT_3D;
+	tx->dim_len = dim_len;
+	tx->lut_3d = lut_3d;
+	tx->base.ref_count = 1;
+	wlr_addon_set_init(&tx->base.addons);
 
 out_lcms_tr:
 	cmsDeleteTransform(lcms_tr);
@@ -115,5 +115,5 @@ out_icc_profile:
 	cmsCloseProfile(icc_profile);
 out_ctx:
 	cmsDeleteContext(ctx);
-	return tx;
+	return &tx->base;
 }

render/vulkan/pass.c

@@ -116,7 +116,14 @@ static bool render_pass_submit(struct wlr_render_pass *wlr_pass) {
 			.uv_off = { 0, 0 },
 			.uv_size = { 1, 1 },
 		};
-		size_t dim = pass->color_transform ? pass->color_transform->lut3d.dim_len : 1;
+
+		size_t dim = 1;
+		if (pass->color_transform && pass->color_transform->type == COLOR_TRANSFORM_LUT_3D) {
+			struct wlr_color_transform_lut3d *lut3d =
+				wlr_color_transform_lut3d_from_base(pass->color_transform);
+			dim = lut3d->dim_len;
+		}
+
 		struct wlr_vk_frag_output_pcr_data frag_pcr_data = {
 			.lut_3d_offset = 0.5f / dim,
 			.lut_3d_scale = (float)(dim - 1) / dim,
@@ -894,7 +901,8 @@ static struct wlr_vk_color_transform *vk_color_transform_create(
 	}
 
 	if (transform->type == COLOR_TRANSFORM_LUT_3D) {
-		if (!create_3d_lut_image(renderer, &transform->lut3d,
+		if (!create_3d_lut_image(renderer,
+				wlr_color_transform_lut3d_from_base(transform),
 				&vk_transform->lut_3d.image,
 				&vk_transform->lut_3d.image_view,
 				&vk_transform->lut_3d.memory,