wlr_scene: Track output damage separately

The damage ring is only supposed to keep track of damage within
the swapchain

include/wlr/types/wlr_scene.h

@@ -206,6 +206,8 @@ struct wlr_scene_output {
 
 	// private state
 
+	pixman_region32_t pending_commit_damage;
+
 	uint8_t index;
 	bool prev_scanout;
 

types/scene/wlr_scene.c

@@ -1277,6 +1277,19 @@ static void scene_output_handle_commit(struct wl_listener *listener, void *data)
 			WLR_OUTPUT_STATE_ENABLED)) {
 		scene_output_update_geometry(scene_output, force_update);
 	}
+
+	// if the output has been committed with a certain damage, we know that region
+	// will be acknowledged by the backend so we don't need to keep track of it
+	// anymore
+	if (state->committed & WLR_OUTPUT_STATE_DAMAGE) {
+		if (wlr_swapchain_has_buffer(scene_output->output->swapchain, state->buffer)) {
+			pixman_region32_subtract(&scene_output->pending_commit_damage,
+				&scene_output->pending_commit_damage, &state->damage);
+		} else {
+			pixman_region32_union(&scene_output->pending_commit_damage,
+				&scene_output->pending_commit_damage, &state->damage);
+		}
+	}
 }
 
 static void scene_output_handle_damage(struct wl_listener *listener, void *data) {
@@ -1306,6 +1319,7 @@ struct wlr_scene_output *wlr_scene_output_create(struct wlr_scene *scene,
 	wlr_addon_init(&scene_output->addon, &output->addons, scene, &output_addon_impl);
 
 	wlr_damage_ring_init(&scene_output->damage_ring);
+	pixman_region32_init(&scene_output->pending_commit_damage);
 	wl_list_init(&scene_output->damage_highlight_regions);
 
 	int prev_output_index = -1;
@@ -1364,6 +1378,7 @@ void wlr_scene_output_destroy(struct wlr_scene_output *scene_output) {
 
 	wlr_addon_finish(&scene_output->addon);
 	wlr_damage_ring_finish(&scene_output->damage_ring);
+	pixman_region32_fini(&scene_output->pending_commit_damage);
 	wl_list_remove(&scene_output->link);
 	wl_list_remove(&scene_output->output_commit.link);
 	wl_list_remove(&scene_output->output_damage.link);
@@ -1467,9 +1482,15 @@ static bool construct_render_list_iterator(struct wlr_scene_node *node,
 
 static void output_state_apply_damage(const struct render_data *data,
 		struct wlr_output_state *state) {
+	struct wlr_scene_output *output = data->output;
+	pixman_region32_union(&output->pending_commit_damage,
+		&output->pending_commit_damage, &output->damage_ring.current);
+	pixman_region32_intersect_rect(&output->pending_commit_damage,
+		&output->pending_commit_damage, 0, 0, data->trans_width, data->trans_height);
+
 	pixman_region32_t frame_damage;
 	pixman_region32_init(&frame_damage);
-	pixman_region32_copy(&frame_damage, &data->output->damage_ring.current);
+	pixman_region32_copy(&frame_damage, &output->pending_commit_damage);
 	transform_output_damage(&frame_damage, data);
 	wlr_output_state_set_damage(state, &frame_damage);
 	pixman_region32_fini(&frame_damage);
@@ -1601,7 +1622,7 @@ static bool scene_entry_try_direct_scanout(struct render_list_entry *entry,
 bool wlr_scene_output_commit(struct wlr_scene_output *scene_output,
 		const struct wlr_scene_output_state_options *options) {
 	if (!scene_output->output->needs_frame && !pixman_region32_not_empty(
-			&scene_output->damage_ring.current)) {
+			&scene_output->pending_commit_damage)) {
 		return true;
 	}