buffer: add wlr_client_buffer.source

This stores a weak reference to the source buffer.

include/wlr/types/wlr_buffer.h

@@ -136,10 +136,15 @@ struct wlr_client_buffer {
 	 * client destroys the buffer before it has been released.
 	 */
 	struct wlr_texture *texture;
+	/**
+	 * The buffer this client buffer was created from. NULL if destroyed.
+	 */
+	struct wlr_buffer *source;
 
 	// private state
 
 	struct wl_listener resource_destroy;
+	struct wl_listener source_destroy;
 
 	// If the client buffer has been created from a wl_shm buffer
 	uint32_t shm_source_format;

types/wlr_buffer.c

@@ -124,6 +124,7 @@ static struct wlr_client_buffer *client_buffer_from_buffer(
 static void client_buffer_destroy(struct wlr_buffer *buffer) {
 	struct wlr_client_buffer *client_buffer = client_buffer_from_buffer(buffer);
 	wl_list_remove(&client_buffer->resource_destroy.link);
+	wl_list_remove(&client_buffer->source_destroy.link);
 	wlr_texture_destroy(client_buffer->texture);
 	free(client_buffer);
 }
@@ -169,6 +170,15 @@ static void client_buffer_resource_handle_destroy(struct wl_listener *listener,
 	// which case we'll read garbage. We decide to accept this risk.
 }
 
+static void client_buffer_handle_source_destroy(struct wl_listener *listener,
+		void *data) {
+	struct wlr_client_buffer *client_buffer =
+		wl_container_of(listener, client_buffer, source_destroy);
+	wl_list_remove(&client_buffer->source_destroy.link);
+	wl_list_init(&client_buffer->source_destroy.link);
+	client_buffer->source = NULL;
+}
+
 static bool buffer_is_shm_client_buffer(struct wlr_buffer *buffer);
 static struct wlr_shm_client_buffer *shm_client_buffer_from_buffer(
 	struct wlr_buffer *buffer);
@@ -224,11 +234,15 @@ struct wlr_client_buffer *wlr_client_buffer_create(struct wlr_buffer *buffer,
 	wlr_buffer_init(&client_buffer->base, &client_buffer_impl,
 		texture->width, texture->height);
 	client_buffer->resource = resource;
+	client_buffer->source = buffer;
 	client_buffer->texture = texture;
 
 	wl_resource_add_destroy_listener(resource, &client_buffer->resource_destroy);
 	client_buffer->resource_destroy.notify = client_buffer_resource_handle_destroy;
 
+	wl_signal_add(&buffer->events.destroy, &client_buffer->source_destroy);
+	client_buffer->source_destroy.notify = client_buffer_handle_source_destroy;
+
 	if (buffer_is_shm_client_buffer(buffer)) {
 		struct wlr_shm_client_buffer *shm_client_buffer =
 			shm_client_buffer_from_buffer(buffer);