monitor-manager: Add API to get scales supported by the backend

For the Xrandr backend, only scale 1 is supported, for the others, 1
and 2 are reported as supported.

https://bugzilla.gnome.org/show_bug.cgi?id=777732

src/backends/meta-monitor-manager-dummy.c

@@ -39,6 +39,11 @@
 #define MAX_CRTCS (MAX_MONITORS * 2)
 #define MAX_MODES (MAX_MONITORS * 4)
 
+static float supported_scales_dummy[] = {
+  1.0,
+  2.0
+};
+
 struct _MetaMonitorManagerDummy
 {
   MetaMonitorManager parent_instance;
@@ -585,6 +590,15 @@ meta_monitor_manager_dummy_calculate_monitor_mode_scale (MetaMonitorManager *man
   return output_dummy->scale;
 }
 
+static void
+meta_monitor_manager_dummy_get_supported_scales (MetaMonitorManager *manager,
+                                                 float             **scales,
+                                                 int                *n_scales)
+{
+  *scales = supported_scales_dummy;
+  *n_scales = G_N_ELEMENTS (supported_scales_dummy);
+}
+
 static void
 meta_monitor_manager_dummy_class_init (MetaMonitorManagerDummyClass *klass)
 {
@@ -596,6 +610,7 @@ meta_monitor_manager_dummy_class_init (MetaMonitorManagerDummyClass *klass)
   manager_class->apply_configuration = meta_monitor_manager_dummy_apply_config;
   manager_class->is_transform_handled = meta_monitor_manager_dummy_is_transform_handled;
   manager_class->calculate_monitor_mode_scale = meta_monitor_manager_dummy_calculate_monitor_mode_scale;
+  manager_class->get_supported_scales = meta_monitor_manager_dummy_get_supported_scales;
 }
 
 static void

src/backends/meta-monitor-manager-private.h

@@ -353,6 +353,10 @@ struct _MetaMonitorManagerClass
   int (*calculate_monitor_mode_scale) (MetaMonitorManager *,
                                        MetaMonitor        *,
                                        MetaMonitorMode    *);
+
+  void (*get_supported_scales) (MetaMonitorManager *,
+                                float             **,
+                                int                *);
 };
 
 void                meta_monitor_manager_rebuild (MetaMonitorManager *manager,

src/backends/native/meta-monitor-manager-kms.c

@@ -52,6 +52,11 @@
 #define ALL_TRANSFORMS_MASK ((1 << ALL_TRANSFORMS) - 1)
 #define SYNC_TOLERANCE 0.01    /* 1 percent */
 
+static float supported_scales_kms[] = {
+  1.0,
+  2.0
+};
+
 typedef struct
 {
   drmModeConnector *connector;
@@ -1904,6 +1909,15 @@ meta_monitor_manager_kms_calculate_monitor_mode_scale (MetaMonitorManager *manag
     return compute_scale (monitor, monitor_mode);
 }
 
+static void
+meta_monitor_manager_kms_get_supported_scales (MetaMonitorManager *manager,
+                                               float             **scales,
+                                               int                *n_scales)
+{
+  *scales = supported_scales_kms;
+  *n_scales = G_N_ELEMENTS (supported_scales_kms);
+}
+
 static void
 meta_monitor_manager_kms_dispose (GObject *object)
 {
@@ -1945,4 +1959,5 @@ meta_monitor_manager_kms_class_init (MetaMonitorManagerKmsClass *klass)
   manager_class->set_crtc_gamma = meta_monitor_manager_kms_set_crtc_gamma;
   manager_class->is_transform_handled = meta_monitor_manager_kms_is_transform_handled;
   manager_class->calculate_monitor_mode_scale = meta_monitor_manager_kms_calculate_monitor_mode_scale;
+  manager_class->get_supported_scales = meta_monitor_manager_kms_get_supported_scales;
 }

src/backends/x11/meta-monitor-manager-xrandr.c

@@ -52,6 +52,10 @@
  * for the reasoning */
 #define DPI_FALLBACK 96.0
 
+static float supported_scales_xrandr[] = {
+  1.0
+};
+
 struct _MetaMonitorManagerXrandr
 {
   MetaMonitorManager parent_instance;
@@ -1583,6 +1587,15 @@ meta_monitor_manager_xrandr_calculate_monitor_mode_scale (MetaMonitorManager *ma
   return 1;
 }
 
+static void
+meta_monitor_manager_xrandr_get_supported_scales (MetaMonitorManager *manager,
+                                                  float             **scales,
+                                                  int                *n_scales)
+{
+  *scales = supported_scales_xrandr;
+  *n_scales = G_N_ELEMENTS (supported_scales_xrandr);
+}
+
 static void
 meta_monitor_manager_xrandr_init (MetaMonitorManagerXrandr *manager_xrandr)
 {
@@ -1660,6 +1673,7 @@ meta_monitor_manager_xrandr_class_init (MetaMonitorManagerXrandrClass *klass)
 #endif
   manager_class->is_transform_handled = meta_monitor_manager_xrandr_is_transform_handled;
   manager_class->calculate_monitor_mode_scale = meta_monitor_manager_xrandr_calculate_monitor_mode_scale;
+  manager_class->get_supported_scales = meta_monitor_manager_xrandr_get_supported_scales;
 
   quark_meta_monitor_xrandr_data =
     g_quark_from_static_string ("-meta-monitor-xrandr-data");

src/tests/meta-monitor-manager-test.c

@@ -23,6 +23,11 @@
 
 #include "backends/meta-monitor-config-manager.h"
 
+static float supported_scales_test[] = {
+  1.0,
+  2.0
+};
+
 struct _MetaMonitorManagerTest
 {
   MetaMonitorManager parent;
@@ -360,6 +365,15 @@ meta_monitor_manager_test_calculate_monitor_mode_scale (MetaMonitorManager *mana
   return output_test->scale;
 }
 
+static void
+meta_monitor_manager_test_get_supported_scales (MetaMonitorManager *manager,
+                                                float             **scales,
+                                                int                *n_scales)
+{
+  *scales = supported_scales_test;
+  *n_scales = G_N_ELEMENTS (supported_scales_test);
+}
+
 static void
 meta_monitor_manager_test_dispose (GObject *object)
 {
@@ -393,4 +407,5 @@ meta_monitor_manager_test_class_init (MetaMonitorManagerTestClass *klass)
   manager_class->tiled_monitor_removed = meta_monitor_manager_test_tiled_monitor_removed;
   manager_class->is_transform_handled = meta_monitor_manager_test_is_transform_handled;
   manager_class->calculate_monitor_mode_scale = meta_monitor_manager_test_calculate_monitor_mode_scale;
+  manager_class->get_supported_scales = meta_monitor_manager_test_get_supported_scales;
 }