scene_output_layout: make output adding explicit

Closes: https://gitlab.freedesktop.org/wlroots/wlroots/-/issues/3709

include/wlr/types/wlr_scene.h

@@ -30,6 +30,7 @@
 
 struct wlr_output;
 struct wlr_output_layout;
+struct wlr_output_layout_output;
 struct wlr_xdg_surface;
 struct wlr_layer_surface_v1;
 struct wlr_drag_icon;
@@ -37,6 +38,7 @@ struct wlr_surface;
 
 struct wlr_scene_node;
 struct wlr_scene_buffer;
+struct wlr_scene_output_layout;
 
 struct wlr_presentation;
 struct wlr_linux_dmabuf_v1;
@@ -515,14 +517,22 @@ struct wlr_scene_output *wlr_scene_get_scene_output(struct wlr_scene *scene,
 /**
  * Attach an output layout to a scene.
  *
- * Adding, removing, or repositioning an output in the output layout
- * will respectively add, remove or reposition a corresponding
- * scene-graph output. When the output layout is destroyed, scene-graph
- * outputs which were created by this helper will be destroyed.
+ * With an attached `wlr_scene_output_layout`, removing or repositioning an output in the output
+ * layout will respectively remove or reposition a corresponding scene-graph output. When the output
+ * layout is destroyed, scene-graph outputs which were attached to this helper will be destroyed.
+ *
+ * When adding an output to the output_layout, users must also create a `wlr_scene_output` and pass
+ * it to wlr_scene_output_layout_add_output().
  */
-bool wlr_scene_attach_output_layout(struct wlr_scene *scene,
+struct wlr_scene_output_layout *wlr_scene_attach_output_layout(struct wlr_scene *scene,
 	struct wlr_output_layout *output_layout);
 
+/**
+ * Add an output to the scene, with its positioning defined by the output layout.
+ */
+void wlr_scene_output_layout_add_output(struct wlr_scene_output_layout *sol,
+	struct wlr_output_layout_output *lo, struct wlr_scene_output *so);
+
 /**
  * Add a node displaying a surface and all of its sub-surfaces to the
  * scene-graph.

tinywl/tinywl.c

@@ -39,6 +39,7 @@ struct tinywl_server {
 	struct wlr_renderer *renderer;
 	struct wlr_allocator *allocator;
 	struct wlr_scene *scene;
+	struct wlr_scene_output_layout *scene_layout;
 
 	struct wlr_xdg_shell *xdg_shell;
 	struct wl_listener new_xdg_surface;
@@ -646,7 +647,10 @@ static void server_new_output(struct wl_listener *listener, void *data) {
 	 * display, which Wayland clients can see to find out information about the
 	 * output (such as DPI, scale factor, manufacturer, etc).
 	 */
-	wlr_output_layout_add_auto(server->output_layout, wlr_output);
+	struct wlr_output_layout_output *l_output = wlr_output_layout_add_auto(server->output_layout,
+		wlr_output);
+	struct wlr_scene_output *scene_output = wlr_scene_output_create(server->scene, wlr_output);
+	wlr_scene_output_layout_add_output(server->scene_layout, l_output, scene_output);
 }
 
 static void xdg_toplevel_map(struct wl_listener *listener, void *data) {
@@ -906,7 +910,7 @@ int main(int argc, char *argv[]) {
 	 * necessary.
 	 */
 	server.scene = wlr_scene_create();
-	wlr_scene_attach_output_layout(server.scene, server.output_layout);
+	server.scene_layout = wlr_scene_attach_output_layout(server.scene, server.output_layout);
 
 	/* Set up xdg-shell version 3. The xdg-shell is a Wayland protocol which is
 	 * used for application windows. For more detail on shells, refer to my

types/scene/output_layout.c

@@ -8,7 +8,6 @@ struct wlr_scene_output_layout {
 
 	struct wl_list outputs; // wlr_scene_output_layout_output.link
 
-	struct wl_listener layout_add;
 	struct wl_listener layout_change;
 	struct wl_listener layout_destroy;
 	struct wl_listener scene_destroy;
@@ -53,7 +52,6 @@ static void scene_output_layout_destroy(struct wlr_scene_output_layout *sol) {
 	wl_list_for_each_safe(solo, tmp, &sol->outputs, link) {
 		scene_output_layout_output_destroy(solo);
 	}
-	wl_list_remove(&sol->layout_add.link);
 	wl_list_remove(&sol->layout_change.link);
 	wl_list_remove(&sol->layout_destroy.link);
 	wl_list_remove(&sol->scene_destroy.link);
@@ -72,19 +70,14 @@ static void scene_output_layout_handle_layout_change(
 	}
 }
 
-static void scene_output_layout_add(struct wlr_scene_output_layout *sol,
-		struct wlr_output_layout_output *lo) {
+void wlr_scene_output_layout_add_output(struct wlr_scene_output_layout *sol,
+		struct wlr_output_layout_output *lo, struct wlr_scene_output *so) {
 	struct wlr_scene_output_layout_output *solo = calloc(1, sizeof(*solo));
 	if (solo == NULL) {
 		return;
 	}
 
-	solo->scene_output = wlr_scene_output_create(sol->scene, lo->output);
-	if (solo->scene_output == NULL) {
-		free(solo);
-		return;
-	}
-
+	solo->scene_output = so;
 	solo->layout_output = lo;
 
 	solo->layout_output_destroy.notify =
@@ -101,15 +94,6 @@ static void scene_output_layout_add(struct wlr_scene_output_layout *sol,
 	wlr_scene_output_set_position(solo->scene_output, lo->x, lo->y);
 }
 
-static void scene_output_layout_handle_layout_add(
-		struct wl_listener *listener, void *data) {
-	struct wlr_scene_output_layout *sol =
-		wl_container_of(listener, sol, layout_add);
-	struct wlr_output_layout_output *lo = data;
-
-	scene_output_layout_add(sol, lo);
-}
-
 static void scene_output_layout_handle_layout_destroy(
 		struct wl_listener *listener, void *data) {
 	struct wlr_scene_output_layout *sol =
@@ -124,11 +108,11 @@ static void scene_output_layout_handle_scene_destroy(
 	scene_output_layout_destroy(sol);
 }
 
-bool wlr_scene_attach_output_layout(struct wlr_scene *scene,
+struct wlr_scene_output_layout *wlr_scene_attach_output_layout(struct wlr_scene *scene,
 		struct wlr_output_layout *output_layout) {
 	struct wlr_scene_output_layout *sol = calloc(1, sizeof(*sol));
 	if (sol == NULL) {
-		return false;
+		return NULL;
 	}
 
 	sol->scene = scene;
@@ -142,16 +126,8 @@ bool wlr_scene_attach_output_layout(struct wlr_scene *scene,
 	sol->layout_change.notify = scene_output_layout_handle_layout_change;
 	wl_signal_add(&output_layout->events.change, &sol->layout_change);
 
-	sol->layout_add.notify = scene_output_layout_handle_layout_add;
-	wl_signal_add(&output_layout->events.add, &sol->layout_add);
-
 	sol->scene_destroy.notify = scene_output_layout_handle_scene_destroy;
 	wl_signal_add(&scene->tree.node.events.destroy, &sol->scene_destroy);
 
-	struct wlr_output_layout_output *lo;
-	wl_list_for_each(lo, &output_layout->outputs, link) {
-		scene_output_layout_add(sol, lo);
-	}
-
-	return true;
+	return sol;
 }