compositor-headless: Support starting with zero outputs

This patch adds a new command line option which can be
used to tell headless backend not to create any
virtual outputs.

This will be used for output hotplug emulation, where
weston will start with no outputs available, and the
virtual output will be created at runtime.

v2:

- Use bool instead of int for the indicator flag
- Move final newspace to a separate line in command
  line options

Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Signed-off-by: Armin Krezović <krezovic.armin@gmail.com>

compositor/main.c

@@ -526,7 +526,9 @@ usage(int error_code)
 		"  --height=HEIGHT\tHeight of memory surface\n"
 		"  --transform=TR\tThe output transformation, TR is one of:\n"
 		"\tnormal 90 180 270 flipped flipped-90 flipped-180 flipped-270\n"
-		"  --use-pixman\t\tUse the pixman (CPU) renderer (default: no rendering)\n\n");
+		"  --use-pixman\t\tUse the pixman (CPU) renderer (default: no rendering)\n"
+		"  --no-outputs\t\tDo not create any virtual outputs\n"
+		"\n");
 #endif
 
 #if defined(BUILD_RDP_COMPOSITOR)
@@ -1037,6 +1039,7 @@ load_headless_backend(struct weston_compositor *c,
 		{ WESTON_OPTION_INTEGER, "height", 0, &config.height },
 		{ WESTON_OPTION_BOOLEAN, "use-pixman", 0, &config.use_pixman },
 		{ WESTON_OPTION_STRING, "transform", 0, &transform },
+		{ WESTON_OPTION_BOOLEAN, "no-outputs", 0, &config.no_outputs },
 	};
 
 	parse_options(options, ARRAY_LENGTH(options), argc, argv);

libweston/compositor-headless.c

@@ -212,8 +212,11 @@ headless_backend_create(struct weston_compositor *compositor,
 	if (b->use_pixman) {
 		pixman_renderer_init(compositor);
 	}
-	if (headless_backend_create_output(b, config) < 0)
-		goto err_input;
+
+	if (!config->no_outputs) {
+		if (headless_backend_create_output(b, config) < 0)
+			goto err_input;
+	}
 
 	if (!b->use_pixman && noop_renderer_init(compositor) < 0)
 		goto err_input;

libweston/compositor-headless.h

@@ -44,6 +44,7 @@ struct weston_headless_backend_config {
 	int use_pixman;
 
 	uint32_t transform;
+	bool no_outputs;
 };
 
 #ifdef  __cplusplus