wlr_scene: Introduce wlr_scene_buffer_set_opacity

include/wlr/types/wlr_scene.h

@@ -166,6 +166,7 @@ struct wlr_scene_buffer {
 
 	// private state
 
+	float opacity;
 	uint64_t active_outputs;
 	struct wlr_texture *texture;
 	struct wlr_fbox src_box;
@@ -415,6 +416,12 @@ void wlr_scene_buffer_set_dest_size(struct wlr_scene_buffer *scene_buffer,
 void wlr_scene_buffer_set_transform(struct wlr_scene_buffer *scene_buffer,
 	enum wl_output_transform transform);
 
+/**
+* Sets the opacity of this buffer
+*/
+void wlr_scene_buffer_set_opacity(struct wlr_scene_buffer *scene_buffer,
+	float opacity);
+
 /**
  * Calls the buffer's frame_done signal.
  */

types/scene/wlr_scene.c

@@ -241,6 +241,10 @@ static void scene_node_opaque_region(struct wlr_scene_node *node, int x, int y,
 			return;
 		}
 
+		if (scene_buffer->opacity != 1) {
+			return;
+		}
+
 		if (!buffer_is_opaque(scene_buffer->buffer)) {
 			pixman_region32_copy(opaque, &scene_buffer->opaque_region);
 			pixman_region32_translate(opaque, x, y);
@@ -604,6 +608,7 @@ struct wlr_scene_buffer *wlr_scene_buffer_create(struct wlr_scene_tree *parent,
 	wl_signal_init(&scene_buffer->events.output_present);
 	wl_signal_init(&scene_buffer->events.frame_done);
 	pixman_region32_init(&scene_buffer->opaque_region);
+	scene_buffer->opacity = 1;
 
 	scene_node_update(&scene_buffer->node, NULL);
 
@@ -794,6 +799,16 @@ void wlr_scene_buffer_send_frame_done(struct wlr_scene_buffer *scene_buffer,
 	}
 }
 
+void wlr_scene_buffer_set_opacity(struct wlr_scene_buffer *scene_buffer,
+		float opacity) {
+	if (scene_buffer->opacity == opacity) {
+		return;
+	}
+
+	scene_buffer->opacity = opacity;
+	scene_node_update(&scene_buffer->node, NULL);
+}
+
 static struct wlr_texture *scene_buffer_get_texture(
 		struct wlr_scene_buffer *scene_buffer, struct wlr_renderer *renderer) {
 	struct wlr_client_buffer *client_buffer =
@@ -1127,6 +1142,7 @@ static void scene_node_render(struct wlr_scene_node *node,
 			.dst_box = dst_box,
 			.transform = transform,
 			.clip = &render_region,
+			.alpha = &scene_buffer->opacity,
 		});
 
 		wl_signal_emit_mutable(&scene_buffer->events.output_present, scene_output);