drm-backend: removing the restriction of exclusively presenting in

plane-assignment

in `drm_output_propose_state`, we are removing the restriction of exclusively
present for view to be assigned on a plane, as in the case of cloning outputs,
no views would fit this condition. Now one view can be assigned to different
planes on different outputs.
Signed-off-by: xichen zhou <sichem.zh@gmail.com>

libweston/backend-drm/state-propose.c

@@ -843,7 +843,13 @@ drm_output_propose_state(struct weston_output *output_base,
 	pixman_region32_init(&planes_region);
 	pixman_region32_init(&occluded_region);
 
-	wl_list_for_each(ev, &output_base->compositor->view_list, link) {
+        /* using output->view_list we could avoid testing if the view touches
+         * the output. Also, since we enable independent overlapping damage
+         * tracking, for cloning outputs, we would need to allow view assign on
+         * different planes in different outputs.
+         */
+	wl_list_for_each(ev, &output_base->view_list,
+	                 output_damages[output_base->id].link) {
 		struct drm_plane_state *ps = NULL;
 		bool force_renderer = false;
 		pixman_region32_t clipped_view;
@@ -854,22 +860,6 @@ drm_output_propose_state(struct weston_output *output_base,
 		          ev, output->base.name,
 			  (unsigned long) output->base.id);
 
-		/* If this view doesn't touch our output at all, there's no
-		 * reason to do anything with it. */
-		if (!(ev->output_mask & (1u << output->base.id))) {
-			drm_debug(b, "\t\t\t\t[view] ignoring view %p "
-			             "(not on our output)\n", ev);
-			continue;
-		}
-
-		/* We only assign planes to views which are exclusively present
-		 * on our output. */
-		if (ev->output_mask != (1u << output->base.id)) {
-			drm_debug(b, "\t\t\t\t[view] not assigning view %p to plane "
-			             "(on multiple outputs)\n", ev);
-			force_renderer = true;
-		}
-
 		if (!weston_view_has_valid_buffer(ev)) {
 			drm_debug(b, "\t\t\t\t[view] not assigning view %p to plane "
 			             "(no buffer available)\n", ev);
@@ -1072,15 +1062,12 @@ drm_assign_planes(struct weston_output *output_base, void *repaint_data)
 	assert(state);
 	drm_debug(b, "\t[repaint] Using %s composition\n",
 		  drm_propose_state_mode_to_string(mode));
-
-	wl_list_for_each(ev, &output_base->compositor->view_list, link) {
+	/* using output->view_list we could avoid testing if the view touches
+	 * the output */
+        wl_list_for_each(ev, &output_base->view_list,
+	                 output_damages[output_base->id].link) {
 		struct drm_plane *target_plane = NULL;
 
-		/* If this view doesn't touch our output at all, there's no
-		 * reason to do anything with it. */
-		if (!(ev->output_mask & (1u << output->base.id)))
-			continue;
-
 		/* Test whether this buffer can ever go into a plane:
 		 * non-shm, or small enough to be a cursor.
 		 *