render/color: add wlr_color_transform_eval()

Makes it so the Vulkan renderer can handle arbitrary color
transforms, and doesn't need to be updated each time a new one is
added.

include/render/color.h

@@ -72,12 +72,6 @@ struct wlr_color_transform_inverse_eotf *wlr_color_transform_inverse_eotf_from_b
 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

@@ -152,4 +152,10 @@ struct wlr_color_transform *wlr_color_transform_ref(struct wlr_color_transform *
  */
 void wlr_color_transform_unref(struct wlr_color_transform *tr);
 
+/**
+ * Evaluate a color transform for a given RGB triplet.
+ */
+void wlr_color_transform_eval(struct wlr_color_transform *tr,
+	float out[static 3], const float in[static 3]);
+
 #endif

render/color.c

@@ -108,6 +108,65 @@ struct wlr_color_transform_lut_3x1d *color_transform_lut_3x1d_from_base(
 	return lut_3x1d;
 }
 
+static float srgb_eval_inverse_eotf(float x) {
+	// See https://www.w3.org/Graphics/Color/srgb
+	if (x <= 0.0031308) {
+		return 12.92 * x;
+	} else {
+		return 1.055 * powf(x, 1.0 / 2.4) - 0.055;
+	}
+}
+
+static float st2084_pq_eval_inverse_eotf(float x) {
+	// H.273 TransferCharacteristics code point 16
+	float c1 = 0.8359375;
+	float c2 = 18.8515625;
+	float c3 = 18.6875;
+	float m = 78.84375;
+	float n = 0.1593017578125;
+	if (x < 0) {
+		x = 0;
+	}
+	if (x > 1) {
+		x = 1;
+	}
+	float pow_n = powf(x, n);
+	return powf((c1 + c2 * pow_n) / (1 + c3 * pow_n), m);
+}
+
+static float bt1886_eval_inverse_eotf(float x) {
+	float lb = powf(0.0001, 1.0 / 2.4);
+	float lw = powf(1.0, 1.0 / 2.4);
+	float a  = powf(lw - lb, 2.4);
+	float b  = lb / (lw - lb);
+	return powf(x / a, 1.0 / 2.4) - b;
+}
+
+static float transfer_function_eval_inverse_eotf(
+		enum wlr_color_transfer_function tf, float x) {
+	switch (tf) {
+	case WLR_COLOR_TRANSFER_FUNCTION_SRGB:
+		return srgb_eval_inverse_eotf(x);
+	case WLR_COLOR_TRANSFER_FUNCTION_ST2084_PQ:
+		return st2084_pq_eval_inverse_eotf(x);
+	case WLR_COLOR_TRANSFER_FUNCTION_EXT_LINEAR:
+		return x;
+	case WLR_COLOR_TRANSFER_FUNCTION_GAMMA22:
+		return powf(x, 1.0 / 2.2);
+	case WLR_COLOR_TRANSFER_FUNCTION_BT1886:
+		return bt1886_eval_inverse_eotf(x);
+	}
+	abort(); // unreachable
+}
+
+static void color_transform_inverse_eotf_eval(
+		struct wlr_color_transform_inverse_eotf *tr,
+		float out[static 3], const float in[static 3]) {
+	for (size_t i = 0; i < 3; i++) {
+		out[i] = transfer_function_eval_inverse_eotf(tr->tf, in[i]);
+	}
+}
+
 static float lut_1d_get(const uint16_t *lut, size_t len, size_t i) {
 	if (i >= len) {
 		i = len - 1;
@@ -125,13 +184,28 @@ static float lut_1d_eval(const uint16_t *lut, size_t len, float x) {
 	return a * (1 - frac_part) + b * frac_part;
 }
 
-void color_transform_lut_3x1d_eval(struct wlr_color_transform_lut_3x1d *tr,
+static 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_transform_eval(struct wlr_color_transform *tr,
+		float out[static 3], const float in[static 3]) {
+	switch (tr->type) {
+	case COLOR_TRANSFORM_INVERSE_EOTF:
+		color_transform_inverse_eotf_eval(wlr_color_transform_inverse_eotf_from_base(tr), out, in);
+		break;
+	case COLOR_TRANSFORM_LCMS2:
+		color_transform_lcms2_eval(color_transform_lcms2_from_base(tr), out, in);
+		break;
+	case COLOR_TRANSFORM_LUT_3X1D:
+		color_transform_lut_3x1d_eval(color_transform_lut_3x1d_from_base(tr), out, in);
+		break;
+	}
+}
+
 void wlr_color_primaries_from_named(struct wlr_color_primaries *out,
 		enum wlr_color_named_primaries named) {
 	switch (named) {

render/vulkan/pass.c

@@ -964,19 +964,6 @@ 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_INVERSE_EOTF:
-		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;
@@ -1074,11 +1061,7 @@ static bool create_3d_lut_image(struct wlr_vk_renderer *renderer,
 					b_index * sample_range,
 				};
 				float rgb_out[3];
-				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);
-				}
+				wlr_color_transform_eval(tr, rgb_out, rgb_in);
 
 				dst[dst_offset] = rgb_out[0];
 				dst[dst_offset + 1] = rgb_out[1];