Fix dynamic output based scaling for menu and SSD

wlr_scene_buffers need an additional wlr_scene_buffer_set_source_box()
to be scaled correctly by wlroots based on the output scale.

With this commit the buffers are now scaled correctly but, especially
on higher scale factors, may be a bit blurry.

In the future we likely want a dynamic font label generator based
on the maximal scale of all the outputs the specific buffer is currently on.

Some inspiration for that could be
https://github.com/Nefsen402/sway/blob/scene-graph/sway/sway_text_buffer.c

Fixes #348

src/menu/menu.c

@@ -75,6 +75,17 @@ menu_get_by_id(const char *id)
 	return NULL;
 }
 
+static struct wlr_scene_node *
+create_scaling_buffer(struct wlr_scene_node *parent, struct wlr_buffer *buffer)
+{
+	struct wlr_scene_buffer *scene_buffer =
+		wlr_scene_buffer_create(parent, buffer);
+	/* Make sure output scaling works correctly */
+	struct wlr_fbox source_box = { 0, 0, buffer->width, buffer->height };
+	wlr_scene_buffer_set_source_box(scene_buffer, &source_box);
+	return &scene_buffer->node;
+}
+
 static struct menuitem *
 item_create(struct menu *menu, const char *text)
 {
@@ -126,10 +137,10 @@ item_create(struct menu *menu, const char *text)
 		theme->menu_items_active_bg_color)->node;
 
 	/* Font nodes */
-	menuitem->normal.text = &wlr_scene_buffer_create(
+	menuitem->normal.text = create_scaling_buffer(
-		menuitem->normal.background, &menuitem->normal.buffer->base)->node;
+		menuitem->normal.background, &menuitem->normal.buffer->base);
-	menuitem->selected.text = &wlr_scene_buffer_create(
+	menuitem->selected.text = create_scaling_buffer(
-		menuitem->selected.background, &menuitem->selected.buffer->base)->node;
+		menuitem->selected.background, &menuitem->selected.buffer->base);
 
 	/* Node descriptors for top scene nodes of menuitem */
 	node_descriptor_create(menuitem->normal.background,

src/ssd/ssd_part.c

@@ -40,7 +40,11 @@ add_scene_buffer(struct wl_list *list, enum ssd_part_type type,
 	int x, int y)
 {
 	struct ssd_part *part = add_scene_part(list, type);
-	part->node = &wlr_scene_buffer_create(parent, buffer)->node;
+	struct wlr_scene_buffer *scene_buffer =
+		wlr_scene_buffer_create(parent, buffer);
+	part->node = &scene_buffer->node;
+	struct wlr_fbox source_box = { 0, 0, buffer->width, buffer->height };
+	wlr_scene_buffer_set_source_box(scene_buffer, &source_box);
 	wlr_scene_node_set_position(part->node, x, y);
 	return part;
 }

src/ssd/ssd_titlebar.c

@@ -221,6 +221,7 @@ ssd_update_title(struct view *view)
 	struct ssd_part *parent_part;
 	struct ssd_sub_tree *subtree;
 	struct ssd_state_title_width *dstate;
+	struct wlr_scene_buffer *scene_buffer;
 	FOR_EACH_STATE(view, subtree) {
 		parent_part = ssd_get_part(&subtree->parts, LAB_SSD_PART_TITLEBAR);
 		assert(parent_part);
@@ -259,11 +260,19 @@ ssd_update_title(struct view *view)
 			wlr_log(WLR_ERROR, "Failed to create title buffer");
 		}
 
+		scene_buffer = wlr_scene_buffer_from_node(part->node);
+
 		/* (Re)set the buffer */
-		wlr_scene_buffer_set_buffer(
+		wlr_scene_buffer_set_buffer(scene_buffer,
-			wlr_scene_buffer_from_node(part->node),
 			part->buffer ? &part->buffer->base : NULL);
 
+		/* Make sure output scaling works correctly */
+		if (part->buffer) {
+			struct wlr_fbox source_box = {0, 0,
+				part->buffer->base.width, part->buffer->base.height };
+			wlr_scene_buffer_set_source_box(scene_buffer, &source_box);
+		}
+
 		/* And finally update the cache */
 		dstate->width = part->buffer ? part->buffer->base.width : 0;
 		dstate->truncated = rect->width <= dstate->width;