color: add from sRGB to blending color transformation

This is needed when the compositor produces any content internally:
- the lines in triangle fan debug
- the censoring color fill (unmet HDCP requirements)

Solid color surfaces do not need this special-casing because
weston_surface is supposed to carry color space information, which will
get used in gl_shader_config_init_for_view().

This makes sure the internally produced graphics fit in, e.g on a
monitor in HDR mode.

For now, just ensure there is an identity transformation. Actual
implementations in GL-renderer will follow later.

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

include/libweston/libweston.h

@@ -375,6 +375,7 @@ struct weston_output {
 
 	bool use_renderer_shadow_buffer;
 	struct weston_color_transform *from_sRGB_to_output;
+	struct weston_color_transform *from_sRGB_to_blend;
 	struct weston_color_transform *from_blend_to_output;
 	bool from_blend_to_output_by_backend;
 

libweston/color-noop.c

@@ -88,6 +88,19 @@ cmnoop_get_sRGB_to_output_color_transform(struct weston_color_manager *cm_base,
 	return true;
 }
 
+static bool
+cmnoop_get_sRGB_to_blend_color_transform(struct weston_color_manager *cm_base,
+					 struct weston_output *output,
+					 struct weston_color_transform **xform_out)
+{
+	/* TODO: Assert output has no colorspace set */
+
+	/* Identity transform */
+	*xform_out = NULL;
+
+	return true;
+}
+
 static bool
 cmnoop_init(struct weston_color_manager *cm_base)
 {
@@ -124,6 +137,8 @@ weston_color_manager_noop_create(struct weston_compositor *compositor)
 	cm->base.get_output_color_transform = cmnoop_get_output_color_transform;
 	cm->base.get_sRGB_to_output_color_transform =
 	      cmnoop_get_sRGB_to_output_color_transform;
+	cm->base.get_sRGB_to_blend_color_transform =
+	      cmnoop_get_sRGB_to_blend_color_transform;
 
 	return &cm->base;
 }

libweston/color.h

@@ -192,6 +192,22 @@ struct weston_color_manager {
 	(*get_sRGB_to_output_color_transform)(struct weston_color_manager *cm,
 					      struct weston_output *output,
 					      struct weston_color_transform **xform_out);
+
+	/** Get sRGB to output's blending space transformation
+	 *
+	 * \param cm The color manager.
+	 * \param output The output for the destination blending color space.
+	 * \param xform_out Pointer for storing the weston_color_transform.
+	 * \return True on success, false on failure.
+	 *
+	 * The callee is responsible for increasing the reference count on the
+	 * weston_color_transform it stores via xform_out. On failure, xform_out
+	 * is untouched.
+	 */
+	bool
+	(*get_sRGB_to_blend_color_transform)(struct weston_color_manager *cm,
+					     struct weston_output *output,
+					     struct weston_color_transform **xform_out);
 };
 
 struct weston_color_transform *

libweston/compositor.c

@@ -6274,6 +6274,8 @@ weston_output_reset_color_transforms(struct weston_output *output)
 {
 	weston_color_transform_unref(output->from_sRGB_to_output);
 	output->from_sRGB_to_output = NULL;
+	weston_color_transform_unref(output->from_sRGB_to_blend);
+	output->from_sRGB_to_blend = NULL;
 	weston_color_transform_unref(output->from_blend_to_output);
 	output->from_blend_to_output = NULL;
 }
@@ -6691,6 +6693,8 @@ weston_output_enable(struct weston_output *output)
 					    &output->from_blend_to_output);
 	ok = ok && cm->get_sRGB_to_output_color_transform(cm, output,
 							  &output->from_sRGB_to_output);
+	ok = ok && cm->get_sRGB_to_blend_color_transform(cm, output,
+							 &output->from_sRGB_to_blend);
 	if (!ok) {
 		weston_log("Creating color transformation for output \"%s\" failed.\n",
 			   output->name);

libweston/renderer-gl/gl-renderer.c

@@ -1034,6 +1034,9 @@ draw_paint_node(struct weston_paint_node *pnode,
 	else
 		filter = GL_NEAREST;
 
+	/* for triangle_fan_debug(), maybe_censor_override() */
+	assert(pnode->output->from_sRGB_to_blend == NULL);
+
 	if (!gl_shader_config_init_for_paint_node(&sconf, pnode, filter))
 		goto out;