main: Add --virtual-monitor argument

Make it possible to create persintent virtual monitors using command
line argument. This will not be the only way to create virtual monitors,
the primary way will be using the screen cast API, but using command
line argumenst is convenient for debugging purposes.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1698>

src/core/main.c

@@ -76,6 +76,8 @@
 #endif
 
 #include "backends/meta-backend-private.h"
+#include "backends/meta-monitor-manager-private.h"
+#include "backends/meta-virtual-monitor.h"
 #include "backends/x11/cm/meta-backend-x11-cm.h"
 #include "backends/x11/meta-backend-x11.h"
 #include "clutter/clutter.h"
@@ -140,6 +142,10 @@ static GMainLoop *meta_main_loop = NULL;
 static void prefs_changed_callback (MetaPreference pref,
                                     gpointer       data);
 
+#ifdef HAVE_NATIVE_BACKEND
+static void release_virtual_monitors (void);
+#endif
+
 /**
  * meta_print_compilation_info:
  *
@@ -213,6 +219,13 @@ static gboolean  opt_headless;
 #endif
 static gboolean  opt_x11;
 
+#ifdef HAVE_NATIVE_BACKEND
+static gboolean opt_virtual_monitor_cb (const char  *option_name,
+                                        const char  *value,
+                                        gpointer     data,
+                                        GError     **error);
+#endif
+
 static GOptionEntry meta_options[] = {
   {
     "sm-disable", 0, 0, G_OPTION_ARG_NONE,
@@ -286,6 +299,11 @@ static GOptionEntry meta_options[] = {
     &opt_headless,
     N_("Run as a headless display server")
   },
+  {
+    "virtual-monitor", 0, 0, G_OPTION_ARG_CALLBACK,
+    &opt_virtual_monitor_cb,
+    N_("Add persistent virtual monitor (WxH or WxH@R)")
+  },
 #endif
   {
     "x11", 0, 0, G_OPTION_ARG_NONE,
@@ -358,6 +376,10 @@ meta_finalize (void)
     meta_wayland_finalize ();
 #endif
 
+#ifdef HAVE_NATIVE_BACKEND
+  release_virtual_monitors ();
+#endif
+
   meta_release_backend ();
 }
 
@@ -458,6 +480,92 @@ check_for_wayland_session_type (void)
 }
 #endif
 
+#ifdef HAVE_NATIVE_BACKEND
+static GList *opt_virtual_monitor_infos = NULL;
+
+static GList *persistent_virtual_monitors = NULL;
+
+static gboolean
+opt_virtual_monitor_cb (const char  *option_name,
+                        const char  *value,
+                        gpointer     data,
+                        GError     **error)
+{
+  int width, height;
+  float refresh_rate = 60.0;
+
+  if (sscanf (value, "%dx%d@%f",
+              &width, &height, &refresh_rate) == 3 ||
+      sscanf (value, "%dx%d",
+              &width, &height) == 2)
+    {
+      g_autofree char *serial = NULL;
+      MetaVirtualMonitorInfo *virtual_monitor;
+
+      serial = g_strdup_printf ("0x%.2x",
+                                g_list_length (opt_virtual_monitor_infos));
+      virtual_monitor = meta_virtual_monitor_info_new (width,
+                                                       height,
+                                                       refresh_rate,
+                                                       "MetaVendor",
+                                                       "MetaVirtualMonitor",
+                                                       serial);
+      opt_virtual_monitor_infos = g_list_append (opt_virtual_monitor_infos,
+                                                 virtual_monitor);
+      return TRUE;
+    }
+  else
+    {
+      return FALSE;
+    }
+}
+
+static void
+release_virtual_monitors (void)
+{
+  g_list_free_full (persistent_virtual_monitors, g_object_unref);
+  persistent_virtual_monitors = NULL;
+}
+
+static void
+add_persistent_virtual_monitors (void)
+{
+  MetaBackend *backend = meta_get_backend ();
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (backend);
+  GList *l;
+
+  for (l = opt_virtual_monitor_infos; l; l = l->next)
+    {
+      MetaVirtualMonitorInfo *info = l->data;
+      g_autoptr (GError) error = NULL;
+      MetaVirtualMonitor *virtual_monitor;
+
+      virtual_monitor =
+        meta_monitor_manager_create_virtual_monitor (monitor_manager,
+                                                     info,
+                                                     &error);
+      if (!virtual_monitor)
+        {
+          g_warning ("Failed to add virtual monitor: %s", error->message);
+          meta_exit (META_EXIT_ERROR);
+        }
+
+      persistent_virtual_monitors = g_list_append (persistent_virtual_monitors,
+                                                   virtual_monitor);
+    }
+
+  if (opt_virtual_monitor_infos)
+    {
+      g_list_free_full (opt_virtual_monitor_infos,
+                        (GDestroyNotify) meta_virtual_monitor_info_free);
+      opt_virtual_monitor_infos = NULL;
+
+      meta_monitor_manager_reload (monitor_manager);
+    }
+}
+#endif
+
 /*
  * Determine the compositor configuration, i.e. whether to run as a Wayland
  * compositor, as well as what backend to use.
@@ -751,6 +859,10 @@ meta_init (void)
       g_array_free (_backend_property_values, TRUE);
     }
 
+#ifdef HAVE_NATIVE_BACKEND
+  add_persistent_virtual_monitors ();
+#endif
+
   meta_set_syncing (opt_sync || (g_getenv ("MUTTER_SYNC") != NULL));
 
   if (opt_replace_wm)