wl-drm: use resource interface

Instead of hardcoding builtin resource types in
wlr_buffer_from_resource(), use the modular resource interface.

types/buffer/resource.c

@@ -2,7 +2,6 @@
 #include <string.h>
 #include <wayland-server.h>
 #include <wlr/interfaces/wlr_buffer.h>
-#include <wlr/types/wlr_drm.h>
 #include <wlr/util/log.h>
 #include "types/wlr_buffer.h"
 
@@ -47,12 +46,6 @@ static const struct wlr_buffer_resource_interface *get_buffer_resource_iface(
 struct wlr_buffer *wlr_buffer_from_resource(struct wl_resource *resource) {
 	assert(resource && wlr_resource_is_buffer(resource));
 
-	struct wlr_buffer *buffer;
-	if (wlr_drm_buffer_is_resource(resource)) {
-		struct wlr_drm_buffer *drm_buffer =
-			wlr_drm_buffer_from_resource(resource);
-		buffer = wlr_buffer_lock(&drm_buffer->base);
-	} else {
 	const struct wlr_buffer_resource_interface *iface =
 			get_buffer_resource_iface(resource);
 	if (!iface) {
@@ -60,14 +53,11 @@ struct wlr_buffer *wlr_buffer_from_resource(struct wl_resource *resource) {
 		return NULL;
 	}
 
-		struct wlr_buffer *custom_buffer = iface->from_resource(resource);
-		if (!custom_buffer) {
+	struct wlr_buffer *buffer = iface->from_resource(resource);
+	if (!buffer) {
 		wlr_log(WLR_ERROR, "Failed to create %s buffer", iface->name);
 		return NULL;
 	}
 
-		buffer = wlr_buffer_lock(custom_buffer);
-	}
-
-	return buffer;
+	return wlr_buffer_lock(buffer);
 }

types/wlr_drm.c

@@ -170,6 +170,17 @@ static void drm_bind(struct wl_client *client, void *data,
 	}
 }
 
+static struct wlr_buffer *buffer_from_resource(struct wl_resource *resource) {
+	struct wlr_drm_buffer *buffer = wlr_drm_buffer_from_resource(resource);
+	return &buffer->base;
+}
+
+static const struct wlr_buffer_resource_interface buffer_resource_interface = {
+	.name = "wlr_drm_buffer",
+	.is_instance = wlr_drm_buffer_is_resource,
+	.from_resource = buffer_from_resource,
+};
+
 static void drm_destroy(struct wlr_drm *drm) {
 	wl_signal_emit_mutable(&drm->events.destroy, NULL);
 
@@ -243,5 +254,7 @@ struct wlr_drm *wlr_drm_create(struct wl_display *display,
 	drm->renderer_destroy.notify = handle_renderer_destroy;
 	wl_signal_add(&renderer->events.destroy, &drm->renderer_destroy);
 
+	wlr_buffer_register_resource_interface(&buffer_resource_interface);
+
 	return drm;
 }