color-lcms: color characteristics into HDR metadata

This is the beginnings of creating composited content HDR metadata for
the ST2084 HDR mode. The immediate goal is to allow essentially setting
the HDR metadata from weston.ini, so that it can be experimented with.

Setting an output ICC profile will stop weston.ini metadata from taking
effect, but using an ICC profile in HDR mode is an open question anyway.

maxDML, maxCLL, and minDML are set based on the assumption that we want
to make use of the full sink/monitor dynamic range.

This also adds several TODOs about how we should handle output profiles,
basic output color characteristics, and HDR metadata. Implementing these
properly will take more thought and effort.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/color-lcms/color-lcms.c

@@ -27,6 +27,7 @@
 #include "config.h"
 
 #include <assert.h>
+#include <string.h>
 #include <libweston/libweston.h>
 
 #include "color.h"
@@ -185,6 +186,102 @@ cmlcms_get_sRGB_to_blend_color_transform(struct weston_color_manager_lcms *cm,
 	return true;
 }
 
+static float
+meta_clamp(float value, const char *valname, float min, float max,
+	   struct weston_output *output)
+{
+	float ret = value;
+
+	/* Paranoia against NaN */
+	if (!(ret >= min))
+		ret = min;
+
+	if (!(ret <= max))
+		ret = max;
+
+	if (ret != value) {
+		weston_log("output '%s' clamping %s value from %f to %f.\n",
+			   output->name, valname, value, ret);
+	}
+
+	return ret;
+}
+
+static bool
+cmlcms_get_hdr_meta(struct weston_output *output,
+		    struct weston_hdr_metadata_type1 *hdr_meta)
+{
+	const struct weston_color_characteristics *cc;
+
+	hdr_meta->group_mask = 0;
+
+	/* Only SMPTE ST 2084 mode uses HDR Static Metadata Type 1 */
+	if (weston_output_get_eotf_mode(output) != WESTON_EOTF_MODE_ST2084)
+		return true;
+
+	/* ICC profile overrides color characteristics */
+	if (output->color_profile) {
+		/*
+		 * TODO: extract characteristics from profile?
+		 * Get dynamic range from weston_color_characteristics?
+		 */
+
+		return true;
+	}
+
+	cc = weston_output_get_color_characteristics(output);
+
+	/* Target content chromaticity */
+	if (cc->group_mask & WESTON_COLOR_CHARACTERISTICS_GROUP_PRIMARIES) {
+		unsigned i;
+
+		for (i = 0; i < 3; i++) {
+			hdr_meta->primary[i].x = meta_clamp(cc->primary[i].x,
+							    "primary", 0.0, 1.0,
+							    output);
+			hdr_meta->primary[i].y = meta_clamp(cc->primary[i].y,
+							    "primary", 0.0, 1.0,
+							    output);
+		}
+		hdr_meta->group_mask |= WESTON_HDR_METADATA_TYPE1_GROUP_PRIMARIES;
+	}
+
+	/* Target content white point */
+	if (cc->group_mask & WESTON_COLOR_CHARACTERISTICS_GROUP_WHITE) {
+		hdr_meta->white.x = meta_clamp(cc->white.x, "white",
+					       0.0, 1.0, output);
+		hdr_meta->white.y = meta_clamp(cc->white.y, "white",
+					       0.0, 1.0, output);
+		hdr_meta->group_mask |= WESTON_HDR_METADATA_TYPE1_GROUP_WHITE;
+	}
+
+	/* Target content peak and max mastering luminance */
+	if (cc->group_mask & WESTON_COLOR_CHARACTERISTICS_GROUP_MAXL) {
+		hdr_meta->maxDML = meta_clamp(cc->max_luminance, "maxDML",
+					      1.0, 65535.0, output);
+		hdr_meta->maxCLL = meta_clamp(cc->max_luminance, "maxCLL",
+					      1.0, 65535.0, output);
+		hdr_meta->group_mask |= WESTON_HDR_METADATA_TYPE1_GROUP_MAXDML;
+		hdr_meta->group_mask |= WESTON_HDR_METADATA_TYPE1_GROUP_MAXCLL;
+	}
+
+	/* Target content min mastering luminance */
+	if (cc->group_mask & WESTON_COLOR_CHARACTERISTICS_GROUP_MINL) {
+		hdr_meta->minDML = meta_clamp(cc->min_luminance, "minDML",
+					      0.0001, 6.5535, output);
+		hdr_meta->group_mask |= WESTON_HDR_METADATA_TYPE1_GROUP_MINDML;
+	}
+
+	/* Target content max frame-average luminance */
+	if (cc->group_mask & WESTON_COLOR_CHARACTERISTICS_GROUP_MAXFALL) {
+		hdr_meta->maxFALL = meta_clamp(cc->maxFALL, "maxFALL",
+					       1.0, 65535.0, output);
+		hdr_meta->group_mask |= WESTON_HDR_METADATA_TYPE1_GROUP_MAXFALL;
+	}
+
+	return true;
+}
+
 static struct weston_output_color_outcome *
 cmlcms_create_output_color_outcome(struct weston_color_manager *cm_base,
 				   struct weston_output *output)
@@ -196,6 +293,19 @@ cmlcms_create_output_color_outcome(struct weston_color_manager *cm_base,
 	if (!co)
 		return NULL;
 
+	if (!cmlcms_get_hdr_meta(output, &co->hdr_meta))
+		goto out_fail;
+
+	/*
+	 * TODO: if output->color_profile is NULL, maybe manufacture a
+	 * profile from weston_color_characteristics if it has enough
+	 * information?
+	 * Or let the frontend decide to call a "create a profile from
+	 * characteristics" API?
+	 */
+
+	/* TODO: take container color space into account */
+
 	if (!cmlcms_get_blend_to_output_color_transform(cm, output,
 							&co->from_blend_to_output))
 		goto out_fail;
@@ -208,8 +318,6 @@ cmlcms_create_output_color_outcome(struct weston_color_manager *cm_base,
 						       &co->from_sRGB_to_output))
 		goto out_fail;
 
-	co->hdr_meta.group_mask = 0;
-
 	return co;
 
 out_fail: