tree-wide: use die_if_null() for wlr_scene alloc failures

wlr_scene_*_create() functions all allocate memory via calloc() and
return NULL if the allocation fails. Previously, the failures were
handled in any of 3 different ways:

 - sending a wayland protocol error
 - exiting labwc with an error
 - segfault (no NULL check at all)

Since labwc does not attempt to survive heap exhaustion in other
allocation paths (such as `znew`), it seems more consistent to use the
same die_if_null() check used in those paths to exit with an error.

For the three most common create() functions (tree, rect, buffer),
add small lab_wlr_ wrappers to common/scene-helpers.

src/cycle/cycle.c

@@ -231,7 +231,7 @@ preview_selected_view(struct view *view)
 	cycle->preview_node = &view->scene_tree->node;
 
 	/* Create a dummy node at the original place of the previewed window */
-	struct wlr_scene_rect *dummy_rect = wlr_scene_rect_create(
+	struct wlr_scene_rect *dummy_rect = lab_wlr_scene_rect_create(
 		cycle->preview_node->parent, 0, 0, (float [4]) {0});
 	wlr_scene_node_place_below(&dummy_rect->node, cycle->preview_node);
 	wlr_scene_node_set_enabled(&dummy_rect->node, false);

src/cycle/osd-classic.c

@@ -9,6 +9,7 @@
 #include "common/lab-scene-rect.h"
 #include "common/list.h"
 #include "common/mem.h"
+#include "common/scene-helpers.h"
 #include "common/string-helpers.h"
 #include "config/rcxml.h"
 #include "cycle.h"
@@ -108,7 +109,7 @@ cycle_osd_classic_init(struct cycle_osd_output *osd_output)
 	int h = workspace_name_h + nr_visible_views * switcher_theme->item_height
 		+ 2 * padding;
 
-	osd_output->tree = wlr_scene_tree_create(output->cycle_osd_tree);
+	osd_output->tree = lab_wlr_scene_tree_create(output->cycle_osd_tree);
 
 	float *text_color = theme->osd_label_text_color;
 	float *bg_color = theme->osd_bg_color;
@@ -161,7 +162,7 @@ cycle_osd_classic_init(struct cycle_osd_output *osd_output)
 
 	float *active_bg_color = switcher_theme->item_active_bg_color;
 	float *active_border_color = switcher_theme->item_active_border_color;
-	osd_output->items_tree = wlr_scene_tree_create(osd_output->tree);
+	osd_output->items_tree = lab_wlr_scene_tree_create(osd_output->tree);
 
 	/* Draw text for each node */
 	struct view *view;
@@ -169,7 +170,7 @@ cycle_osd_classic_init(struct cycle_osd_output *osd_output)
 		struct cycle_osd_classic_item *item = znew(*item);
 		wl_list_append(&osd_output->items, &item->base.link);
 		item->base.view = view;
-		item->base.tree = wlr_scene_tree_create(osd_output->items_tree);
+		item->base.tree = lab_wlr_scene_tree_create(osd_output->items_tree);
 		node_descriptor_create(&item->base.tree->node,
 			LAB_NODE_CYCLE_OSD_ITEM, NULL, item);
 		/*
@@ -191,8 +192,8 @@ cycle_osd_classic_init(struct cycle_osd_output *osd_output)
 		int x = padding
 			+ switcher_theme->item_active_border_width
 			+ switcher_theme->item_padding_x;
-		item->normal_tree = wlr_scene_tree_create(item->base.tree);
-		item->active_tree = wlr_scene_tree_create(item->base.tree);
+		item->normal_tree = lab_wlr_scene_tree_create(item->base.tree);
+		item->active_tree = lab_wlr_scene_tree_create(item->base.tree);
 		wlr_scene_node_set_enabled(&item->active_tree->node, false);
 
 		/* Highlight around selected window's item */
@@ -209,7 +210,7 @@ cycle_osd_classic_init(struct cycle_osd_output *osd_output)
 		wlr_scene_node_set_position(&highlight_rect->tree->node, padding, y);
 
 		/* hitbox for mouse clicks */
-		struct wlr_scene_rect *hitbox = wlr_scene_rect_create(item->base.tree,
+		struct wlr_scene_rect *hitbox = lab_wlr_scene_rect_create(item->base.tree,
 			w - 2 * padding, switcher_theme->item_height, (float[4]) {0});
 		wlr_scene_node_set_position(&hitbox->node, padding, y);
 

src/cycle/osd-scroll.c

@@ -2,6 +2,7 @@
 #include <assert.h>
 #include <wlr/types/wlr_scene.h>
 #include "common/lab-scene-rect.h"
+#include "common/scene-helpers.h"
 #include "labwc.h"
 #include "cycle.h"
 #include "output.h"
@@ -23,7 +24,7 @@ cycle_osd_scroll_init(struct cycle_osd_output *osd_output, struct wlr_box bar_ar
 	scroll->top_row_idx = 0;
 	scroll->bar_area = bar_area;
 	scroll->delta_y = delta_y;
-	scroll->bar_tree = wlr_scene_tree_create(osd_output->tree);
+	scroll->bar_tree = lab_wlr_scene_tree_create(osd_output->tree);
 	wlr_scene_node_set_position(&scroll->bar_tree->node,
 		bar_area.x, bar_area.y);
 

src/cycle/osd-thumbnail.c

@@ -10,6 +10,7 @@
 #include "common/lab-scene-rect.h"
 #include "common/list.h"
 #include "common/mem.h"
+#include "common/scene-helpers.h"
 #include "cycle.h"
 #include "labwc.h"
 #include "node.h"
@@ -138,7 +139,7 @@ create_item_scene(struct wlr_scene_tree *parent, struct view *view,
 
 	struct cycle_osd_thumbnail_item *item = znew(*item);
 	wl_list_append(&osd_output->items, &item->base.link);
-	struct wlr_scene_tree *tree = wlr_scene_tree_create(parent);
+	struct wlr_scene_tree *tree = lab_wlr_scene_tree_create(parent);
 	node_descriptor_create(&tree->node, LAB_NODE_CYCLE_OSD_ITEM, NULL, item);
 	item->base.tree = tree;
 	item->base.view = view;
@@ -155,14 +156,14 @@ create_item_scene(struct wlr_scene_tree *parent, struct view *view,
 	item->active_bg = lab_scene_rect_create(tree, &opts);
 
 	/* hitbox for mouse clicks */
-	wlr_scene_rect_create(tree, switcher_theme->item_width,
+	lab_wlr_scene_rect_create(tree, switcher_theme->item_width,
 		switcher_theme->item_height, (float[4]) {0});
 
 	/* thumbnail */
 	struct wlr_buffer *thumb_buffer = render_thumb(osd_output->output, view);
 	if (thumb_buffer) {
 		struct wlr_scene_buffer *thumb_scene_buffer =
-			wlr_scene_buffer_create(tree, thumb_buffer);
+			lab_wlr_scene_buffer_create(tree, thumb_buffer);
 		wlr_buffer_drop(thumb_buffer);
 		struct wlr_box thumb_box = box_fit_within(
 			thumb_buffer->width, thumb_buffer->height,
@@ -239,8 +240,8 @@ cycle_osd_thumbnail_init(struct cycle_osd_output *osd_output)
 		&theme->osd_window_switcher_thumbnail;
 	int padding = theme->osd_border_width + switcher_theme->padding;
 
-	osd_output->tree = wlr_scene_tree_create(output->cycle_osd_tree);
-	osd_output->items_tree = wlr_scene_tree_create(osd_output->tree);
+	osd_output->tree = lab_wlr_scene_tree_create(output->cycle_osd_tree);
+	osd_output->items_tree = lab_wlr_scene_tree_create(osd_output->tree);
 
 	int nr_views = wl_list_length(&server->cycle.views);
 	assert(nr_views > 0);