render: add wlr_renderer_init_wl_shm

This allows compositors to initialize wl_shm without initializing
other globals like linux-dmabuf.

include/wlr/render/wlr_renderer.h

@@ -99,13 +99,19 @@ bool wlr_renderer_read_pixels(struct wlr_renderer *r, uint32_t fmt,
 	uint32_t src_x, uint32_t src_y, uint32_t dst_x, uint32_t dst_y, void *data);
 
 /**
- * Creates necessary shm and invokes the initialization of the implementation.
+ * Initializes wl_shm, linux-dmabuf and other buffer factory protocols.
  *
  * Returns false on failure.
  */
 bool wlr_renderer_init_wl_display(struct wlr_renderer *r,
 	struct wl_display *wl_display);
 
+/**
+ * Initializes wl_shm on the provided wl_display.
+ */
+bool wlr_renderer_init_wl_shm(struct wlr_renderer *r,
+	struct wl_display *wl_display);
+
 /**
  * Obtains the FD of the DRM device used for rendering, or -1 if unavailable.
  *

render/wlr_renderer.c

@@ -202,17 +202,18 @@ bool wlr_renderer_read_pixels(struct wlr_renderer *r, uint32_t fmt,
 		src_x, src_y, dst_x, dst_y, data);
 }
 
-bool wlr_renderer_init_wl_display(struct wlr_renderer *r,
+bool wlr_renderer_init_wl_shm(struct wlr_renderer *r,
 		struct wl_display *wl_display) {
-	if (wl_display_init_shm(wl_display)) {
-		wlr_log(WLR_ERROR, "Failed to initialize shm");
+	if (wl_display_init_shm(wl_display) != 0) {
+		wlr_log(WLR_ERROR, "Failed to initialize wl_shm");
 		return false;
 	}
 
 	size_t len;
 	const uint32_t *formats = wlr_renderer_get_shm_texture_formats(r, &len);
 	if (formats == NULL) {
-		wlr_log(WLR_ERROR, "Failed to initialize shm: cannot get formats");
+		wlr_log(WLR_ERROR, "Failed to initialize wl_shm: "
+			"cannot get renderer formats");
 		return false;
 	}
 
@@ -229,11 +230,24 @@ bool wlr_renderer_init_wl_display(struct wlr_renderer *r,
 			xrgb8888 = true;
 			break;
 		default:
-			wl_display_add_shm_format(wl_display, fmt);
+			if (wl_display_add_shm_format(wl_display, fmt) == NULL) {
+				wlr_log(WLR_ERROR, "Failed to initialize wl_shm: "
+					"failed to add format");
+				return false;
+			}
 		}
 	}
 	assert(argb8888 && xrgb8888);
 
+	return true;
+}
+
+bool wlr_renderer_init_wl_display(struct wlr_renderer *r,
+		struct wl_display *wl_display) {
+	if (!wlr_renderer_init_wl_shm(r, wl_display)) {
+		return false;
+	}
+
 	if (wlr_renderer_get_dmabuf_texture_formats(r) != NULL) {
 		if (wlr_renderer_get_drm_fd(r) >= 0) {
 			if (wlr_drm_create(wl_display, r) == NULL) {