[mutter] monitor-config-manager: Fallback to closed laptop lid configuration

[Jonas Ådahl <jadahl src gnome org>]

commit e48516679c02bb265a80d6680a4ea34d188127e0
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Thu Apr 16 00:28:05 2020 +0200

    monitor-config-manager: Fallback to closed laptop lid configuration
    
    When closing the lid of a laptop, we reconfigure all the monitors in order
    to update the CRTCs and (if enabled) the global UI scaling factor.
    
    To do this, we try first to reuse the current configuration for the usable
    monitors, but if we have only monitor enabled and this one is on the laptop
    lid we just end up creating a new configuration where the primary monitor is
    the laptop one (as per find_primary_monitor() in MetaMonitorConfigManager),
    but ignoring the user parameters.
    
    In case the user selected a different resolution / scaling compared to the
    default one, while the laptop lid is closed we might change the monitors
    layout, causing applications to rescale or reposition.
    
    To avoid this, when creating the monitors configuration from the current
    current state, in case we have only one monitor available and that one is
    the laptop panel, let's just reuse this configuration.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1200

 src/backends/meta-monitor-config-manager.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)
---
diff --git a/src/backends/meta-monitor-config-manager.c b/src/backends/meta-monitor-config-manager.c
index cc9159683..6a7c807bf 100644
--- a/src/backends/meta-monitor-config-manager.c
+++ b/src/backends/meta-monitor-config-manager.c
@@ -446,23 +446,35 @@ MetaMonitorsConfigKey *
 meta_create_monitors_config_key_for_current_state (MetaMonitorManager *monitor_manager)
 {
   MetaMonitorsConfigKey *config_key;
+  MetaMonitorSpec *laptop_monitor_spec;
   GList *l;
   GList *monitor_specs;
 
+  laptop_monitor_spec = NULL;
   monitor_specs = NULL;
   for (l = monitor_manager->monitors; l; l = l->next)
     {
       MetaMonitor *monitor = l->data;
       MetaMonitorSpec *monitor_spec;
 
-      if (meta_monitor_is_laptop_panel (monitor) &&
-          is_lid_closed (monitor_manager))
-        continue;
+      if (meta_monitor_is_laptop_panel (monitor))
+        {
+          laptop_monitor_spec = meta_monitor_get_spec (monitor);
+
+          if (is_lid_closed (monitor_manager))
+            continue;
+        }
 
       monitor_spec = meta_monitor_spec_clone (meta_monitor_get_spec (monitor));
       monitor_specs = g_list_prepend (monitor_specs, monitor_spec);
     }
 
+  if (!monitor_specs && laptop_monitor_spec)
+    {
+      monitor_specs =
+        g_list_prepend (NULL, meta_monitor_spec_clone (laptop_monitor_spec));
+    }
+
   if (!monitor_specs)
     return NULL;