x11 backend: add wlr_output_is_x11

backend/x11/backend.c

@@ -401,3 +401,7 @@ static struct wlr_output_impl output_impl = {
 	.make_current = output_make_current,
 	.swap_buffers = output_swap_buffers,
 };
+
+bool wlr_output_is_x11(struct wlr_output *wlr_output) {
+	return wlr_output->impl == &output_impl;
+}

include/backend/x11.h

@@ -6,7 +6,6 @@
 #include <X11/Xlib-xcb.h>
 #include <wayland-server.h>
 #include <wlr/render/egl.h>
-#include <wlr/types/wlr_output.h>
 #include <wlr/types/wlr_input_device.h>
 
 struct wlr_x11_backend;

include/wlr/backend/x11.h

@@ -4,10 +4,12 @@
 #include <stdbool.h>
 #include <wayland-server.h>
 #include <wlr/backend.h>
+#include <wlr/types/wlr_output.h>
 
 struct wlr_backend *wlr_x11_backend_create(struct wl_display *display,
 	const char *x11_display);
 
 bool wlr_backend_is_x11(struct wlr_backend *backend);
+bool wlr_output_is_x11(struct wlr_output *output);
 
 #endif