monitor-manager: check for underscan setting validity upfront

Instead of doing a roundtrip to the X server before setting it, rely on
the previous value fetched before the configuration was sent over DBus.
This matches the argument check we already do elsewhere, and will allow
us to more easily add an additional condition to determine if underscan
is supported.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/673


(cherry picked from commit 8665084df15190adc0d18cc77b7fcb738d3e4fa6)

1 files changed, 13 insertions, 1 deletions

diff --git a/src/backends/meta-monitor-manager.c b/src/backends/meta-monitor-manager.c
index 41036ca2a..0210aee33 100644
--- a/src/backends/meta-monitor-manager.c
+++ b/src/backends/meta-monitor-manager.c
@@ -1648,6 +1648,7 @@ create_monitor_config_from_variant (MetaMonitorManager *manager,
   MetaMonitorModeSpec *monitor_mode_spec;
   g_autoptr (GVariant) properties_variant = NULL;
   gboolean enable_underscanning = FALSE;
+  gboolean set_underscanning = FALSE;
 
   g_variant_get (monitor_config_variant, "(ss@a{sv})",
                  &connector,
@@ -1670,7 +1671,18 @@ create_monitor_config_from_variant (MetaMonitorManager *manager,
       return NULL;
     }
 
-  g_variant_lookup (properties_variant, "underscanning", "b", &enable_underscanning);
+  set_underscanning =
+    g_variant_lookup (properties_variant, "underscanning", "b",
+                      &enable_underscanning);
+  if (set_underscanning)
+    {
+      if (enable_underscanning && !meta_monitor_supports_underscanning (monitor))
+        {
+          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+                       "Underscanning requested but unsupported");
+          return NULL;
+        }
+    }
 
   monitor_spec = meta_monitor_spec_clone (meta_monitor_get_spec (monitor));