Merge branch 'sunli1/wlroots-output_layers_v3' into 'master'

wlr_scene: Implement Output Layers

See merge request wlroots/wlroots!4348

include/util/array.h

@@ -15,4 +15,15 @@ void array_remove_at(struct wl_array *arr, size_t offset, size_t size);
  */
 bool array_realloc(struct wl_array *arr, size_t size);
 
+/**
+ * Returns a pointer to the first valid element in a reversed array.
+ */
+void *array_reversed_start(struct wl_array *arr);
+
+/**
+ * Adds a new element to the array inserting them starting from a higher
+ * memory address effectively inserting them in reverse order.
+ */
+void *array_reversed_add(struct wl_array *arr, size_t size);
+
 #endif

include/wlr/types/wlr_damage_ring.h

@@ -13,11 +13,20 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <pixman.h>
-
+#include <wayland-server-core.h>
-/* For triple buffering, a history of two frames is required. */
-#define WLR_DAMAGE_RING_PREVIOUS_LEN 2
 
 struct wlr_box;
+struct wlr_buffer;
+
+struct wlr_damage_ring_entry {
+	pixman_region32_t damage;
+	struct wlr_buffer *buffer;
+
+	struct wl_listener buffer_destroy;
+
+	struct wlr_damage_ring *ring;
+	struct wl_list link; // struct wlr_damage_ring.previous
+};
 
 struct wlr_damage_ring {
 	int32_t width, height;
@@ -27,8 +36,7 @@ struct wlr_damage_ring {
 
 	// private state
 
-	pixman_region32_t previous[WLR_DAMAGE_RING_PREVIOUS_LEN];
+	struct wl_list previous; // struct wlr_damage_ring_entry.link
-	size_t previous_idx;
 };
 
 void wlr_damage_ring_init(struct wlr_damage_ring *ring);
@@ -81,4 +89,14 @@ void wlr_damage_ring_rotate(struct wlr_damage_ring *ring);
 void wlr_damage_ring_get_buffer_damage(struct wlr_damage_ring *ring,
 	int buffer_age, pixman_region32_t *damage);
 
+/**
+ * Get the since accumulated damage for this buffer. These buffers should
+ * typically come from a wlr_swapchain. In the context of rendering, the
+ * damage is the region that needs to be redrawn.
+ *
+ * The damage ring is automatically rotated during invocation.
+ */
+void wlr_damage_ring_damage_for_buffer(struct wlr_damage_ring *ring,
+	struct wlr_buffer *buffer, pixman_region32_t *damage);
+
 #endif

include/wlr/types/wlr_scene.h

@@ -110,6 +110,8 @@ struct wlr_scene {
 	enum wlr_scene_debug_damage_option debug_damage_option;
 	bool direct_scanout;
 	bool calculate_visibility;
+
+	struct wl_array render_list;
 };
 
 /** A scene-graph node displaying a single surface. */
@@ -204,6 +206,8 @@ struct wlr_scene_output {
 
 	// private state
 
+	pixman_region32_t pending_commit_damage;
+
 	uint8_t index;
 	bool prev_scanout;
 
@@ -213,7 +217,7 @@ struct wlr_scene_output {
 
 	struct wl_list damage_highlight_regions;
 
-	struct wl_array render_list;
+	struct wl_array output_layers;
 };
 
 struct wlr_scene_timer {

types/scene/wlr_scene.c

@@ -9,6 +9,7 @@
 #include <wlr/types/wlr_damage_ring.h>
 #include <wlr/types/wlr_matrix.h>
 #include <wlr/types/wlr_linux_dmabuf_v1.h>
+#include <wlr/types/wlr_output_layer.h>
 #include <wlr/types/wlr_presentation_time.h>
 #include <wlr/types/wlr_scene.h>
 #include <wlr/util/log.h>
@@ -125,6 +126,8 @@ void wlr_scene_node_destroy(struct wlr_scene_node *node) {
 
 			wl_list_remove(&scene->presentation_destroy.link);
 			wl_list_remove(&scene->linux_dmabuf_v1_destroy.link);
+
+			wl_array_release(&scene->render_list);
 		} else {
 			assert(node->parent);
 		}
@@ -1104,8 +1107,10 @@ struct wlr_scene_node *wlr_scene_node_at(struct wlr_scene_node *node,
 
 struct render_list_entry {
 	struct wlr_scene_node *node;
+	struct wlr_output_layer_state *state;
 	bool sent_dmabuf_feedback;
 	int x, y;
+	bool visible;
 };
 
 static void scene_entry_render(struct render_list_entry *entry, const struct render_data *data) {
@@ -1273,6 +1278,14 @@ static void scene_output_handle_commit(struct wl_listener *listener, void *data)
 			WLR_OUTPUT_STATE_ENABLED)) {
 		scene_output_update_geometry(scene_output);
 	}
+
+	// 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) {
+		pixman_region32_subtract(&scene_output->pending_commit_damage,
+			&scene_output->pending_commit_damage, &state->damage);
+	}
 }
 
 static void scene_output_handle_damage(struct wl_listener *listener, void *data) {
@@ -1302,6 +1315,7 @@ 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;
@@ -1360,12 +1374,14 @@ 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);
 	wl_list_remove(&scene_output->output_needs_frame.link);
 
-	wl_array_release(&scene_output->render_list);
+	wl_array_release(&scene_output->output_layers);
+
 	free(scene_output);
 }
 
@@ -1415,57 +1431,84 @@ struct render_list_constructor_data {
 	bool calculate_visibility;
 };
 
-static bool construct_render_list_iterator(struct wlr_scene_node *node,
+static bool scene_construct_render_list(struct wlr_scene_node *node,
-		int lx, int ly, void *_data) {
+		struct wl_array *render_list, struct wlr_box *box, bool calculate_visibility,
-	struct render_list_constructor_data *data = _data;
+		bool enabled, int lx, int ly) {
 
-	if (scene_node_invisible(node)) {
+	enabled = enabled && node->enabled;
+
+	if (node->type == WLR_SCENE_NODE_TREE) {
+		struct wlr_scene_tree *scene_tree = wlr_scene_tree_from_node(node);
+		struct wlr_scene_node *child;
+		wl_list_for_each_reverse(child, &scene_tree->children, link) {
+			if (!scene_construct_render_list(child, render_list, box, calculate_visibility, enabled,
+					lx + child->x, ly + child->y)) {
 				return false;
 			}
+		}
+
+		return true;
+	}
+
+	struct render_list_entry *entry = wl_array_add(render_list, sizeof(*entry));
+	if (!entry) {
+		return false;
+	}
+
+	memset(entry, 0, sizeof(*entry));
+	entry->node = node;
+	entry->x = lx;
+	entry->y = ly;
+
+	if (!enabled) {
+		return true;
+	}
+
+	struct wlr_box node_box = { .x = lx, .y = ly };
+	scene_node_get_size(node, &node_box.width, &node_box.height);
+
+	if (!wlr_box_intersection(&node_box, &node_box, box) || scene_node_invisible(node)) {
+		return true;
+	}
 
 	// while rendering, the background should always be black.
 	// If we see a black rect, we can ignore rendering everything under the rect
 	// and even the rect itself.
-	if (node->type == WLR_SCENE_NODE_RECT && data->calculate_visibility) {
+	if (node->type == WLR_SCENE_NODE_RECT && calculate_visibility) {
 		struct wlr_scene_rect *rect = wlr_scene_rect_from_node(node);
 		float *black = (float[4]){ 0.f, 0.f, 0.f, 1.f };
 
 		if (memcmp(rect->color, black, sizeof(float) * 4) == 0) {
-			return false;
+			return true;
 		}
 	}
 
 	pixman_region32_t intersection;
 	pixman_region32_init(&intersection);
 	pixman_region32_intersect_rect(&intersection, &node->visible,
-			data->box.x, data->box.y,
+		box->x, box->y, box->width, box->height);
-			data->box.width, data->box.height);
 	if (!pixman_region32_not_empty(&intersection)) {
 		pixman_region32_fini(&intersection);
-		return false;
+		return true;
 	}
 
 	pixman_region32_fini(&intersection);
 
-	struct render_list_entry *entry = wl_array_add(data->render_list, sizeof(*entry));
+	entry->visible = true;
-	if (!entry) {
+	return true;
-		return false;
-	}
-
-	*entry = (struct render_list_entry){
-		.node = node,
-		.x = lx,
-		.y = ly,
-	};
-
-	return false;
 }
 
 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);
@@ -1595,10 +1638,263 @@ static bool scene_entry_try_direct_scanout(struct render_list_entry *entry,
 	return true;
 }
 
+static bool scene_buffer_can_be_output_layer(struct wlr_scene_buffer *buffer,
+		struct wlr_scene_output *scene_output) {
+	struct wlr_fbox default_box = {0};
+	if (buffer->transform & WL_OUTPUT_TRANSFORM_90) {
+		default_box.width = buffer->buffer->height;
+		default_box.height = buffer->buffer->width;
+	} else {
+		default_box.width = buffer->buffer->width;
+		default_box.height = buffer->buffer->height;
+	}
+
+	if (!wlr_fbox_empty(&buffer->src_box) &&
+			!wlr_fbox_equal(&buffer->src_box, &default_box)) {
+		return false;
+	}
+
+	if (buffer->transform != scene_output->output->transform) {
+		return false;
+	}
+
+	return true;
+}
+
+struct wlr_scene_node_output_layer {
+	struct wlr_addon addon;
+	struct wlr_output_layer *layer;
+	struct wlr_scene_buffer *buffer;
+	struct wlr_scene_output *output;
+	struct render_list_entry *current_render_entry;
+
+	struct wl_listener layer_feedback;
+	struct wl_listener output_destroy;
+};
+
+static void node_output_layer_destroy(struct wlr_scene_node_output_layer *layer) {
+	wlr_output_layer_destroy(layer->layer);
+	wlr_addon_finish(&layer->addon);
+	wl_list_remove(&layer->output_destroy.link);
+	free(layer);
+}
+
+static void handle_output_layer_addon_finish(struct wlr_addon *addon) {
+	struct wlr_scene_node_output_layer *layer = wl_container_of(addon, layer, addon);
+	node_output_layer_destroy(layer);
+}
+
+static void handle_output_layer_output_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_scene_node_output_layer *layer = wl_container_of(listener, layer, output_destroy);
+	wl_list_remove(&layer->layer_feedback.link);
+	node_output_layer_destroy(layer);
+}
+
+static const struct wlr_addon_interface node_addon_output_layer = {
+	.name = "wlr_scene_output_layer",
+	.destroy = handle_output_layer_addon_finish,
+};
+
+static struct wlr_scene_node_output_layer *scene_node_get_output_layer(
+		struct wlr_scene_node *node, struct wlr_scene_output *output) {
+	struct wlr_addon *addon = wlr_addon_find(
+		&node->addons, output, &node_addon_output_layer);
+	if (!addon) {
+		return NULL;
+	}
+
+	struct wlr_scene_node_output_layer *layer = wl_container_of(addon, layer, addon);
+	return layer;
+}
+
+static void output_handle_layer_feedback(struct wl_listener *listener, void *data) {
+	struct wlr_scene_node_output_layer *layer =
+		wl_container_of(listener, layer, layer_feedback);
+	struct wlr_output_layer_feedback_event *event = data;
+	struct wlr_linux_dmabuf_feedback_v1_init_options options = {
+		.main_renderer = layer->buffer->primary_output->output->renderer,
+		.output_layer_feedback_event = event,
+	};
+
+	if (layer->buffer->primary_output == layer->output) {
+		scene_buffer_send_dmabuf_feedback(scene_node_get_root(&layer->buffer->node),
+			layer->buffer, &options);
+		layer->current_render_entry->sent_dmabuf_feedback = true;
+	}
+}
+
+static struct wlr_scene_node_output_layer *scene_buffer_create_output_layer(
+		struct wlr_scene_buffer *buffer, struct wlr_scene_output *output) {
+	struct wlr_scene_node_output_layer *layer = calloc(1, sizeof(*layer));
+	if (!layer) {
+		return NULL;
+	}
+
+	layer->layer = wlr_output_layer_create(output->output);
+	if (!layer->layer) {
+		free(layer);
+		return NULL;
+	}
+
+	layer->layer_feedback.notify = output_handle_layer_feedback;
+	wl_signal_add(&layer->layer->events.feedback, &layer->layer_feedback);
+
+	layer->output_destroy.notify = handle_output_layer_output_destroy;
+	wl_signal_add(&output->output->events.destroy, &layer->output_destroy);
+
+	layer->buffer = buffer;
+	layer->output = output;
+
+	wlr_addon_init(&layer->addon, &buffer->node.addons, output, &node_addon_output_layer);
+	return layer;
+}
+
+static bool scene_submit_output_layers(struct wlr_scene_output *scene_output,
+		struct wlr_output_state *state, struct wl_array *render_list) {
+	// if we render software cursors, that means they will be a part of the
+	// primary plane. If we render output layers, it means we could render
+	// over the cursor. A lock will also be registered if there is screen share.
+	// Screen share cannot use output layers.
+	if (scene_output->output->software_cursor_locks) {
+		return false;
+	}
+
+	if (scene_output->scene->debug_damage_option ==
+			WLR_SCENE_DEBUG_DAMAGE_HIGHLIGHT) {
+		return false;
+	}
+
+	struct render_list_entry *list_data = render_list->data;
+	int list_len = render_list->size / sizeof(*list_data);
+
+	scene_output->output_layers.size = 0;
+	if (!array_realloc(&scene_output->output_layers,
+			list_len * sizeof(struct wlr_output_layer_state))) {
+		return false;
+	}
+
+	// area of that the base layer must render (such as rects)
+	pixman_region32_t base_layer_area;
+	pixman_region32_init(&base_layer_area);
+
+	for (int i = 0; i < list_len; i++) {
+		struct render_list_entry *entry = &list_data[i];
+		struct wlr_scene_node *node = entry->node;
+
+		if (node->type != WLR_SCENE_NODE_BUFFER) {
+			continue;
+		}
+
+		struct wlr_box box = { .x = entry->x, .y = entry->y };
+		scene_node_get_size(node, &box.width, &box.height);
+
+		box.x = floor(box.x * scene_output->output->scale) - scene_output->x;
+		box.y = floor(box.y * scene_output->output->scale) - scene_output->y;
+		box.width = ceil(box.width * scene_output->output->scale);
+		box.height = ceil(box.height * scene_output->output->scale);
+
+		struct wlr_scene_node_output_layer *layer =
+			scene_node_get_output_layer(node, scene_output);
+
+		struct wlr_scene_buffer *buffer = wlr_scene_buffer_from_node(node);
+
+		if (entry->visible && !scene_buffer_can_be_output_layer(buffer, scene_output)) {
+			pixman_region32_union_rect(&base_layer_area, &base_layer_area,
+				box.x, box.y, box.width, box.height);
+
+			if (layer) {
+				node_output_layer_destroy(layer);
+			}
+
+			continue;
+		}
+
+		if (entry->visible && !layer) {
+			layer = scene_buffer_create_output_layer(buffer, scene_output);
+			if (!layer) {
+				pixman_region32_union_rect(&base_layer_area, &base_layer_area,
+					box.x, box.y, box.width, box.height);
+				continue;
+			}
+		}
+
+		if (layer) {
+			// we preallocted the array length, this should never return NULL.
+			entry->state = array_reversed_add(&scene_output->output_layers, sizeof(*entry->state));
+
+			layer->current_render_entry = entry;
+			*entry->state = (struct wlr_output_layer_state){
+				.layer = layer->layer,
+				.buffer = NULL,
+				.dst_box = box,
+			};
+		}
+
+		if (!entry->visible) {
+			continue;
+		}
+
+		pixman_region32_t intersection;
+		pixman_region32_init(&intersection);
+		pixman_region32_intersect_rect(&intersection, &base_layer_area,
+			box.x, box.y, box.width, box.height);
+		if (pixman_region32_not_empty(&intersection)) {
+			pixman_region32_union_rect(&base_layer_area, &base_layer_area,
+				box.x, box.y, box.width, box.height);
+			pixman_region32_fini(&intersection);
+			continue;
+		}
+		pixman_region32_fini(&intersection);
+
+		// only consider nodes that are in the damage
+		pixman_region32_init(&intersection);
+		pixman_region32_intersect_rect(&intersection, &scene_output->damage_ring.current,
+			box.x, box.y, box.width, box.height);
+		if (!pixman_region32_not_empty(&intersection)) {
+			pixman_region32_union_rect(&base_layer_area, &base_layer_area,
+				box.x, box.y, box.width, box.height);
+			pixman_region32_fini(&intersection);
+			continue;
+		}
+
+		if (!buffer_is_opaque(buffer->buffer)) {
+			// With transparent nodes, we can't get away with just having the
+			// node partially in the damage or else the user can see through
+			// the node to find an older version of the node software composited
+			// in the base layer.
+			pixman_region32_t node_box;
+			pixman_region32_init_rect(&node_box, box.x, box.y, box.width, box.height);
+			pixman_region32_subtract(&intersection, &node_box, &intersection);
+			pixman_region32_fini(&node_box);
+			if (pixman_region32_not_empty(&intersection)) {
+				pixman_region32_union_rect(&base_layer_area, &base_layer_area,
+					box.x, box.y, box.width, box.height);
+				pixman_region32_fini(&intersection);
+				continue;
+			}
+		}
+		pixman_region32_fini(&intersection);
+
+		entry->state->buffer = buffer->buffer;
+	}
+
+	pixman_region32_fini(&base_layer_area);
+
+	wlr_output_state_set_layers(state, array_reversed_start(&scene_output->output_layers),
+		scene_output->output_layers.size / sizeof(struct wlr_output_layer_state));
+
+	if (!wlr_output_test_state(scene_output->output, state)) {
+		return false;
+	}
+
+	return true;
+}
+
 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;
 	}
 
@@ -1614,8 +1910,6 @@ bool wlr_scene_output_commit(struct wlr_scene_output *scene_output,
 		goto out;
 	}
 
-	wlr_damage_ring_rotate(&scene_output->damage_ring);
-
 out:
 	wlr_output_state_finish(&state);
 	return ok;
@@ -1679,22 +1973,64 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 	render_data.logical.width = render_data.trans_width / render_data.scale;
 	render_data.logical.height = render_data.trans_height / render_data.scale;
 
-	struct render_list_constructor_data list_con = {
+	bool calculate_visibility = scene_output->scene->calculate_visibility;
-		.box = render_data.logical,
+	struct wlr_scene_node *tree_node = &scene_output->scene->tree.node;
-		.render_list = &scene_output->render_list,
+	struct wl_array *render_list = &scene_output->scene->render_list;
-		.calculate_visibility = scene_output->scene->calculate_visibility,
+	int x, y;
+
+	render_list->size = 0;
+	wlr_scene_node_coords(tree_node, &x, &y);
+
+	// There is at least one render list entry for the scene tree itself, therefore
+	// construct_render_list should always return true.
+	if (!scene_construct_render_list(tree_node, render_list, &render_data.logical,
+			calculate_visibility, true, x, y)) {
+		return false;
+	}
+	array_realloc(render_list, render_list->size);
+
+	scene_submit_output_layers(scene_output, state, render_list);
+
+	// Find number of visible render entries. If only one, try direct scanout.
+	struct render_list_entry *list_data = render_list->data;
+	struct render_list_entry *scanout_entry = NULL;
+	int list_len = render_list->size / sizeof(*list_data);
+	int render_count = 0;
+	pixman_region32_t forward_damage;
+	pixman_region32_init(&forward_damage);
+
+	for (int i = list_len - 1; i >= 0; i--) {
+		struct render_list_entry *entry = &list_data[i];
+		if (!entry->visible) {
+			continue;
+		}
+
+		if (entry->state && entry->state->accepted && entry->state->buffer) {
+			// we need to damage the output here for the next frame because since
+			// the we're using output layers here. The contents won't be part
+			// of the primary plane and will therefore have stale contents.
+			pixman_region32_union(&forward_damage, &forward_damage, &entry->node->visible);
+
+			struct wlr_scene_buffer *buffer = wlr_scene_buffer_from_node(entry->node);
+			struct wlr_scene_output_sample_event sample_event = {
+				.output = scene_output,
+				.direct_scanout = true,
 			};
+			wl_signal_emit_mutable(&buffer->events.output_sample, &sample_event);
 
-	list_con.render_list->size = 0;
+			continue;
-	scene_nodes_in_box(&scene_output->scene->tree.node, &list_con.box,
+		}
-		construct_render_list_iterator, &list_con);
-	array_realloc(list_con.render_list, list_con.render_list->size);
 
-	struct render_list_entry *list_data = list_con.render_list->data;
+		scanout_entry = entry;
-	int list_len = list_con.render_list->size / sizeof(*list_data);
+		render_count++;
+	}
 
-	bool scanout = list_len == 1 &&
+	pixman_region32_translate(&forward_damage, -scene_output->x, -scene_output->y);
-		scene_entry_try_direct_scanout(&list_data[0], state, &render_data);
+	scale_output_damage(&forward_damage, scene_output->output->scale);
+	pixman_region32_intersect(&forward_damage, &forward_damage, &scene_output->damage_ring.current);
+
+	bool scanout = render_count == 1 &&
+		scene_entry_try_direct_scanout(scanout_entry, state, &render_data);
 
 	if (scene_output->prev_scanout != scanout) {
 		scene_output->prev_scanout = scanout;
@@ -1713,6 +2049,10 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 			timespec_sub(&duration, &end_time, &start_time);
 			timer->pre_render_duration = timespec_to_nsec(&duration);
 		}
+
+		wlr_damage_ring_add(&scene_output->damage_ring, &forward_damage);
+		pixman_region32_fini(&forward_damage);
+
 		return true;
 	}
 
@@ -1765,9 +2105,9 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 		return false;
 	}
 
-	int buffer_age;
+	struct wlr_buffer *buffer = wlr_swapchain_acquire(output->swapchain, NULL);
-	struct wlr_buffer *buffer = wlr_swapchain_acquire(output->swapchain, &buffer_age);
 	if (buffer == NULL) {
+		pixman_region32_fini(&forward_damage);
 		return false;
 	}
 
@@ -1786,13 +2126,16 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 	});
 	if (render_pass == NULL) {
 		wlr_buffer_unlock(buffer);
+		pixman_region32_fini(&forward_damage);
 		return false;
 	}
 
 	render_data.render_pass = render_pass;
+
+	output_state_apply_damage(&render_data, state);
 	pixman_region32_init(&render_data.damage);
-	wlr_damage_ring_get_buffer_damage(&scene_output->damage_ring,
+	wlr_damage_ring_damage_for_buffer(&scene_output->damage_ring, buffer,
-		buffer_age, &render_data.damage);
+		&render_data.damage);
 
 	pixman_region32_t background;
 	pixman_region32_init(&background);
@@ -1805,6 +2148,10 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 		for (int i = list_len - 1; i >= 0; i--) {
 			struct render_list_entry *entry = &list_data[i];
 
+			if (!entry->visible) {
+				continue;
+			}
+
 			// We must only cull opaque regions that are visible by the node.
 			// The node's visibility will have the knowledge of a black rect
 			// that may have been omitted from the render list via the black
@@ -1840,6 +2187,15 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 
 	for (int i = list_len - 1; i >= 0; i--) {
 		struct render_list_entry *entry = &list_data[i];
+
+		if (!entry->visible) {
+			continue;
+		}
+
+		if (entry->state && entry->state->accepted && entry->state->buffer) {
+			continue;
+		}
+
 		scene_entry_render(entry, &render_data);
 
 		if (entry->node->type == WLR_SCENE_NODE_BUFFER) {
@@ -1877,19 +2233,26 @@ bool wlr_scene_output_build_state(struct wlr_scene_output *scene_output,
 	pixman_region32_fini(&render_data.damage);
 
 	if (!wlr_render_pass_submit(render_pass)) {
+		pixman_region32_fini(&forward_damage);
 		wlr_buffer_unlock(buffer);
+
+		// if we failed to render the buffer, it will have undefined contents
+		// Trash the damage ring
+		wlr_damage_ring_add_whole(&scene_output->damage_ring);
 		return false;
 	}
 
 	wlr_output_state_set_buffer(state, buffer);
 	wlr_buffer_unlock(buffer);
-	output_state_apply_damage(&render_data, state);
 
 	if (debug_damage == WLR_SCENE_DEBUG_DAMAGE_HIGHLIGHT &&
 			!wl_list_empty(&scene_output->damage_highlight_regions)) {
 		wlr_output_schedule_frame(scene_output->output);
 	}
 
+	wlr_damage_ring_add(&scene_output->damage_ring, &forward_damage);
+	pixman_region32_fini(&forward_damage);
+
 	return true;
 }
 

types/wlr_damage_ring.c

@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <pixman.h>
+#include <wlr/types/wlr_buffer.h>
 #include <wlr/types/wlr_damage_ring.h>
 #include <wlr/util/box.h>
 
@@ -14,15 +15,25 @@ void wlr_damage_ring_init(struct wlr_damage_ring *ring) {
 	};
 
 	pixman_region32_init(&ring->current);
-	for (size_t i = 0; i < WLR_DAMAGE_RING_PREVIOUS_LEN; ++i) {
+	wl_list_init(&ring->previous);
-		pixman_region32_init(&ring->previous[i]);
 }
+
+static void entry_destroy(struct wlr_damage_ring_entry *entry) {
+	if (entry->buffer) {
+		wl_list_remove(&entry->buffer_destroy.link);
+	}
+
+	wl_list_remove(&entry->link);
+	pixman_region32_fini(&entry->damage);
+	free(entry);
 }
 
 void wlr_damage_ring_finish(struct wlr_damage_ring *ring) {
 	pixman_region32_fini(&ring->current);
-	for (size_t i = 0; i < WLR_DAMAGE_RING_PREVIOUS_LEN; ++i) {
+
-		pixman_region32_fini(&ring->previous[i]);
+	struct wlr_damage_ring_entry *entry, *tmp_entry;
+	wl_list_for_each_safe(entry, tmp_entry, &ring->previous, link) {
+		entry_destroy(entry);
 	}
 }
 
@@ -79,28 +90,41 @@ void wlr_damage_ring_add_whole(struct wlr_damage_ring *ring) {
 }
 
 void wlr_damage_ring_rotate(struct wlr_damage_ring *ring) {
-	// modular decrement
+	struct wlr_damage_ring_entry *last =
-	ring->previous_idx = ring->previous_idx +
+		wl_container_of(ring->previous.prev, last, link);
-		WLR_DAMAGE_RING_PREVIOUS_LEN - 1;
+	wl_list_remove(&last->link);
-	ring->previous_idx %= WLR_DAMAGE_RING_PREVIOUS_LEN;
+	wl_list_insert(&ring->previous, &last->link);
 
-	pixman_region32_copy(&ring->previous[ring->previous_idx], &ring->current);
+	pixman_region32_copy(&last->damage, &ring->current);
 	pixman_region32_clear(&ring->current);
 }
 
 void wlr_damage_ring_get_buffer_damage(struct wlr_damage_ring *ring,
 		int buffer_age, pixman_region32_t *damage) {
-	if (buffer_age <= 0 || buffer_age - 1 > WLR_DAMAGE_RING_PREVIOUS_LEN) {
-		pixman_region32_clear(damage);
-		pixman_region32_union_rect(damage, damage,
-			0, 0, ring->width, ring->height);
-	} else {
 	pixman_region32_copy(damage, &ring->current);
 
 	// Accumulate damage from old buffers
-		for (int i = 0; i < buffer_age - 1; ++i) {
+	struct wlr_damage_ring_entry *entry;
-			int j = (ring->previous_idx + i) % WLR_DAMAGE_RING_PREVIOUS_LEN;
+	wl_list_for_each(entry, &ring->previous, link) {
-			pixman_region32_union(damage, damage, &ring->previous[j]);
+		if (--buffer_age <= 0) {
+			break;
+		}
+
+		pixman_region32_union(damage, damage, &entry->damage);
+	}
+
+	// if our buffer age is older than anything we are keeping track of, increase
+	// the size
+	if (buffer_age > 0) {
+		pixman_region32_clear(damage);
+		pixman_region32_union_rect(damage, damage,
+			0, 0, ring->width, ring->height);
+
+		struct wlr_damage_ring_entry *entry = calloc(1, sizeof(*entry));
+		if (entry) {
+			pixman_region32_init(&entry->damage);
+			wl_list_insert(ring->previous.prev, &entry->link);
+		}
 	}
 
 	// Check the number of rectangles
@@ -113,4 +137,76 @@ void wlr_damage_ring_get_buffer_damage(struct wlr_damage_ring *ring,
 			extents->y2 - extents->y1);
 	}
 }
+
+static void entry_squash_damage(struct wlr_damage_ring_entry *entry) {
+	pixman_region32_t *prev;
+	if (entry->link.prev == &entry->ring->previous) {
+		// this entry is the first in the list
+		prev = &entry->ring->current;
+	} else {
+		struct wlr_damage_ring_entry *last =
+			wl_container_of(entry->link.prev, last, link);
+		prev = &last->damage;
+	}
+
+	pixman_region32_union(prev, prev, &entry->damage);
+}
+
+static void handle_buffer_destroy(struct wl_listener *listener, void *data) {
+	struct wlr_damage_ring_entry *entry =
+		wl_container_of(listener, entry, buffer_destroy);
+	entry_squash_damage(entry);
+	entry_destroy(entry);
+}
+
+void wlr_damage_ring_damage_for_buffer(struct wlr_damage_ring *ring,
+		struct wlr_buffer *buffer, pixman_region32_t *damage) {
+	pixman_region32_copy(damage, &ring->current);
+
+	struct wlr_damage_ring_entry *entry;
+	wl_list_for_each(entry, &ring->previous, link) {
+		if (entry->buffer != buffer) {
+			pixman_region32_union(damage, damage, &entry->damage);
+			continue;
+		}
+
+		// Check the number of rectangles
+		int n_rects = pixman_region32_n_rects(damage);
+		if (n_rects > WLR_DAMAGE_RING_MAX_RECTS) {
+			pixman_box32_t *extents = pixman_region32_extents(damage);
+			pixman_region32_union_rect(damage, damage,
+				extents->x1, extents->y1,
+				extents->x2 - extents->x1,
+				extents->y2 - extents->y1);
+		}
+
+		// rotate
+		entry_squash_damage(entry);
+		pixman_region32_copy(&entry->damage, &ring->current);
+		pixman_region32_clear(&ring->current);
+
+		wl_list_remove(&entry->link);
+		wl_list_insert(&ring->previous, &entry->link);
+		return;
+	}
+
+	pixman_region32_clear(damage);
+	pixman_region32_union_rect(damage, damage,
+		0, 0, ring->width, ring->height);
+
+	entry = calloc(1, sizeof(*entry));
+	if (!entry) {
+		return;
+	}
+
+	pixman_region32_init(&entry->damage);
+	pixman_region32_copy(&entry->damage, &ring->current);
+	pixman_region32_clear(&ring->current);
+
+	wl_list_insert(&ring->previous, &entry->link);
+	entry->buffer = buffer;
+	entry->ring = ring;
+
+	entry->buffer_destroy.notify = handle_buffer_destroy;
+	wl_signal_add(&buffer->events.destroy, &entry->buffer_destroy);
 }

util/array.c

@@ -38,3 +38,26 @@ bool array_realloc(struct wl_array *arr, size_t size) {
 	arr->alloc = alloc;
 	return true;
 }
+
+void *array_reversed_start(struct wl_array *arr) {
+	char *data = arr->data;
+	return data + arr->alloc - arr->size;
+}
+
+void *array_reversed_add(struct wl_array *arr, size_t size) {
+	if (arr->size + size > arr->alloc) {
+		size_t new_alloc = arr->alloc * 2;
+		char *new = malloc(new_alloc);
+		if (!new) {
+			return NULL;
+		}
+
+		memcpy(new + (new_alloc - arr->size), array_reversed_start(arr), arr->size);
+		free(arr->data);
+		arr->data = new;
+		arr->alloc = new_alloc;
+	}
+
+	arr->size += size;
+	return array_reversed_start(arr);
+}