render/color: add wlr_color_transfer_function_get_default_luminance()

include/render/color.h

@@ -56,4 +56,10 @@ void wlr_color_primaries_from_named(struct wlr_color_primaries *out,
  */
 void wlr_color_primaries_to_xyz(const struct wlr_color_primaries *primaries, float matrix[static 9]);
 
+/**
+ * Get default luminances for a transfer function.
+ */
+void wlr_color_transfer_function_get_default_luminance(enum wlr_color_transfer_function tf,
+	struct wlr_color_luminances *lum);
+
 #endif

include/wlr/render/color.h

@@ -42,6 +42,13 @@ struct wlr_color_primaries {
 	struct wlr_color_cie1931_xy red, green, blue, white;
 };
 
+/**
+ * Luminance range and reference white luminance level, in cd/m².
+ */
+struct wlr_color_luminances {
+	float min, max, reference;
+};
+
 /**
  * A color transformation formula, which maps a linear color space with
  * sRGB primaries to an output color space.

render/color.c

@@ -128,3 +128,23 @@ void wlr_color_primaries_to_xyz(const struct wlr_color_primaries *primaries, flo
 	};
 	memcpy(matrix, result, sizeof(result));
 }
+
+void wlr_color_transfer_function_get_default_luminance(enum wlr_color_transfer_function tf,
+		struct wlr_color_luminances *lum) {
+	switch (tf) {
+	case WLR_COLOR_TRANSFER_FUNCTION_ST2084_PQ:
+		*lum = (struct wlr_color_luminances){
+			.min = 0.005,
+			.max = 10000,
+			.reference = 203,
+		};
+		break;
+	default:
+		*lum = (struct wlr_color_luminances){
+			.min = 0.2,
+			.max = 80,
+			.reference = 80,
+		};
+		break;
+	}
+}