backend: use global output name counters

The output names must be globally unique per the Wayland spec, even
if the compositor creates multiple backends of the same kind.

backend/headless/output.c

@@ -10,6 +10,8 @@ static const uint32_t SUPPORTED_OUTPUT_STATE =
 	WLR_OUTPUT_STATE_BUFFER |
 	WLR_OUTPUT_STATE_MODE;
 
+static size_t last_output_num = 0;
+
 static struct wlr_headless_output *headless_output_from_output(
 		struct wlr_output *wlr_output) {
 	assert(wlr_output_is_headless(wlr_output));
@@ -116,13 +118,14 @@ struct wlr_output *wlr_headless_add_output(struct wlr_backend *wlr_backend,
 
 	output_set_custom_mode(output, width, height, 0);
 
+	size_t output_num = ++last_output_num;
+
 	char name[64];
-	snprintf(name, sizeof(name), "HEADLESS-%zu", ++backend->last_output_num);
+	snprintf(name, sizeof(name), "HEADLESS-%zu", output_num);
 	wlr_output_set_name(wlr_output, name);
 
 	char description[128];
-	snprintf(description, sizeof(description),
-		"Headless output %zu", backend->last_output_num);
+	snprintf(description, sizeof(description), "Headless output %zu", output_num);
 	wlr_output_set_description(wlr_output, description);
 
 	struct wl_event_loop *ev = wl_display_get_event_loop(backend->display);

backend/wayland/output.c

@@ -32,6 +32,8 @@ static const uint32_t SUPPORTED_OUTPUT_STATE =
 	WLR_OUTPUT_STATE_MODE |
 	WLR_OUTPUT_STATE_ADAPTIVE_SYNC_ENABLED;
 
+static size_t last_output_num = 0;
+
 static struct wlr_wl_output *get_wl_output_from_output(
 		struct wlr_output *wlr_output) {
 	assert(wlr_output_is_wl(wlr_output));
@@ -525,13 +527,14 @@ struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
 
 	wlr_output->adaptive_sync_status = WLR_OUTPUT_ADAPTIVE_SYNC_ENABLED;
 
+	size_t output_num = ++last_output_num;
+
 	char name[64];
-	snprintf(name, sizeof(name), "WL-%zu", ++backend->last_output_num);
+	snprintf(name, sizeof(name), "WL-%zu", output_num);
 	wlr_output_set_name(wlr_output, name);
 
 	char description[128];
-	snprintf(description, sizeof(description),
-		"Wayland output %zu", backend->last_output_num);
+	snprintf(description, sizeof(description), "Wayland output %zu", output_num);
 	wlr_output_set_description(wlr_output, description);
 
 	output->backend = backend;

backend/x11/output.c

@@ -29,6 +29,8 @@ static const uint32_t SUPPORTED_OUTPUT_STATE =
 	WLR_OUTPUT_STATE_MODE |
 	WLR_OUTPUT_STATE_ADAPTIVE_SYNC_ENABLED;
 
+static size_t last_output_num = 0;
+
 static void parse_xcb_setup(struct wlr_output *output,
 		xcb_connection_t *xcb) {
 	const xcb_setup_t *xcb_setup = xcb_get_setup(xcb);
@@ -518,15 +520,16 @@ struct wlr_output *wlr_x11_output_create(struct wlr_backend *backend) {
 
 	wlr_output_update_custom_mode(wlr_output, 1024, 768, 0);
 
+	size_t output_num = ++last_output_num;
+
 	char name[64];
-	snprintf(name, sizeof(name), "X11-%zu", ++x11->last_output_num);
+	snprintf(name, sizeof(name), "X11-%zu", output_num);
 	wlr_output_set_name(wlr_output, name);
 
 	parse_xcb_setup(wlr_output, x11->xcb);
 
 	char description[128];
-	snprintf(description, sizeof(description),
-		"X11 output %zu", x11->last_output_num);
+	snprintf(description, sizeof(description), "X11 output %zu", output_num);
 	wlr_output_set_description(wlr_output, description);
 
 	// The X11 protocol requires us to set a colormap and border pixel if the

include/backend/headless.h

@@ -10,7 +10,6 @@ struct wlr_headless_backend {
 	struct wlr_backend backend;
 	struct wl_display *display;
 	struct wl_list outputs;
-	size_t last_output_num;
 	struct wl_listener display_destroy;
 	bool started;
 };

include/backend/wayland.h

@@ -25,7 +25,6 @@ struct wlr_wl_backend {
 	int drm_fd;
 	struct wl_list buffers; // wlr_wl_buffer.link
 	size_t requested_outputs;
-	size_t last_output_num;
 	struct wl_listener local_display_destroy;
 	char *activation_token;
 

include/backend/x11.h

@@ -74,7 +74,6 @@ struct wlr_x11_backend {
 	uint32_t dri3_major_version, dri3_minor_version;
 
 	size_t requested_outputs;
-	size_t last_output_num;
 	struct wl_list outputs; // wlr_x11_output::link
 
 	struct wlr_keyboard keyboard;