From 4ca5a97ea80a1ea5b9f8c8f32de70e503c2049bb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marco=20Trevisan=20=28Trevi=C3=B1o=29?= <mail@3v1n0.net>
Date: Thu, 29 Nov 2018 23:51:55 -0500
Subject: [PATCH] monitor-manager: Only derive global scales supported by all
 monitors

When deriving the global scale from current monitor, we were just checking the
supported value by the primary monitor, without considering weather the current
scale was supported by other monitors.

Resolve this by checking if the picked global scale is valid for all active
monitors, and if it's not the case, use a fallback strategy by just picking the
maximum scale level supported by every head.

Fixes https://gitlab.gnome.org/GNOME/mutter/issues/407

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/336>
---
 src/backends/meta-monitor-manager.c | 65 ++++++++++++++++++++++-------
 1 file changed, 51 insertions(+), 14 deletions(-)

diff --git a/src/backends/meta-monitor-manager.c b/src/backends/meta-monitor-manager.c
index 1d42cad21..9ab846c67 100644
--- a/src/backends/meta-monitor-manager.c
+++ b/src/backends/meta-monitor-manager.c
@@ -119,9 +119,6 @@ static gboolean
 meta_monitor_manager_is_config_complete (MetaMonitorManager *manager,
                                          MetaMonitorsConfig *config);
 
-static MetaMonitor *
-meta_monitor_manager_get_active_monitor (MetaMonitorManager *manager);
-
 static void
 meta_monitor_manager_real_read_current_state (MetaMonitorManager *manager);
 
@@ -245,20 +242,66 @@ calculate_monitor_scale (MetaMonitorManager *manager,
                                                             monitor_mode);
 }
 
+static gboolean
+meta_monitor_manager_is_scale_supported_by_other_monitors (MetaMonitorManager *manager,
+                                                           MetaMonitor        *not_this_one,
+                                                           float               scale)
+{
+  GList *l;
+
+  for (l = manager->monitors; l; l = l->next)
+    {
+      MetaMonitor *monitor = l->data;
+      MetaMonitorMode *mode;
+
+      if (monitor == not_this_one || !meta_monitor_is_active (monitor))
+        continue;
+
+      mode = meta_monitor_get_current_mode (monitor);
+      if (!meta_monitor_manager_is_scale_supported (manager,
+                                                    manager->layout_mode,
+                                                    monitor, mode, scale))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
 static float
 derive_calculated_global_scale (MetaMonitorManager *manager)
 {
   MetaMonitor *monitor = NULL;
+  float scale;
+  GList *l;
 
+  scale = 1.0;
   monitor = meta_monitor_manager_get_primary_monitor (manager);
 
-  if (!monitor || !meta_monitor_is_active (monitor))
-    monitor = meta_monitor_manager_get_active_monitor (manager);
+  if (monitor && meta_monitor_is_active (monitor))
+    {
+      scale = calculate_monitor_scale (manager, monitor);
+      if (meta_monitor_manager_is_scale_supported_by_other_monitors (manager,
+                                                                     monitor,
+                                                                     scale))
+        return scale;
+    }
 
-  if (!monitor)
-    return 1.0;
+  for (l = manager->monitors; l; l = l->next)
+    {
+      MetaMonitor *other_monitor = l->data;
+      float monitor_scale;
 
-  return calculate_monitor_scale (manager, monitor);
+      if (other_monitor == monitor || !meta_monitor_is_active (other_monitor))
+        continue;
+
+      monitor_scale = calculate_monitor_scale (manager, other_monitor);
+      if (meta_monitor_manager_is_scale_supported_by_other_monitors (manager,
+                                                                     other_monitor,
+                                                                     monitor_scale))
+        scale = MAX (scale, monitor_scale);
+    }
+
+  return scale;
 }
 
 static float
@@ -2800,12 +2843,6 @@ meta_monitor_manager_get_laptop_panel (MetaMonitorManager *manager)
   return find_monitor (manager, meta_monitor_is_laptop_panel);
 }
 
-static MetaMonitor *
-meta_monitor_manager_get_active_monitor (MetaMonitorManager *manager)
-{
-  return find_monitor (manager, meta_monitor_is_active);
-}
-
 MetaMonitor *
 meta_monitor_manager_get_monitor_from_connector (MetaMonitorManager *manager,
                                                  const char         *connector)