output: Make implementations inherit MetaOutput

Instead of the home baked "inheritance" system, using a gpointer and a
GDestroyNotify function to keep the what effectively is sub type
details, make MetaOutput an abstract derivable type, and make the
implementations inherit it.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1287

src/tests/headless-start-test.c

@@ -163,7 +163,7 @@ meta_test_headless_monitor_connect (void)
   output_info->possible_crtcs = possible_crtcs;
   output_info->connector_type = META_CONNECTOR_TYPE_DisplayPort;
 
-  output = g_object_new (META_TYPE_OUTPUT,
+  output = g_object_new (META_TYPE_OUTPUT_TEST,
                          "id", 1,
                          "gpu", gpu,
                          "info", output_info,

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

@@ -28,6 +28,8 @@
 #include "backends/meta-output.h"
 #include "tests/meta-backend-test.h"
 
+G_DEFINE_TYPE (MetaOutputTest, meta_output_test, META_TYPE_OUTPUT)
+
 struct _MetaMonitorManagerTest
 {
   MetaMonitorManager parent;
@@ -296,7 +298,7 @@ meta_monitor_manager_test_calculate_monitor_mode_scale (MetaMonitorManager *mana
   MetaOutputTest *output_test;
 
   output = meta_monitor_get_main_output (monitor);
-  output_test = output->driver_private;
+  output_test = META_OUTPUT_TEST (output);
 
   if (output_test)
     return output_test->scale;
@@ -423,3 +425,14 @@ meta_monitor_manager_test_class_init (MetaMonitorManagerTestClass *klass)
   manager_class->get_max_screen_size = meta_monitor_manager_test_get_max_screen_size;
   manager_class->get_default_layout_mode = meta_monitor_manager_test_get_default_layout_mode;
 }
+
+static void
+meta_output_test_init (MetaOutputTest *output_test)
+{
+  output_test->scale = 1;
+}
+
+static void
+meta_output_test_class_init (MetaOutputTestClass *klass)
+{
+}

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

@@ -21,6 +21,7 @@
 #define META_MONITOR_MANAGER_TEST_H
 
 #include "backends/meta-monitor-manager-private.h"
+#include "backends/meta-output.h"
 
 typedef struct _MetaMonitorTestSetup
 {
@@ -29,13 +30,20 @@ typedef struct _MetaMonitorTestSetup
   GList *crtcs;
 } MetaMonitorTestSetup;
 
-typedef struct _MetaOutputTest
+struct _MetaOutputTest
 {
+  MetaOutput parent;
+
   float scale;
-} MetaOutputTest;
+};
 
 typedef MetaMonitorTestSetup * (* CreateTestSetupFunc) (void);
 
+#define META_TYPE_OUTPUT_TEST (meta_output_test_get_type ())
+G_DECLARE_FINAL_TYPE (MetaOutputTest, meta_output_test,
+                      META, OUTPUT_TEST,
+                      MetaOutput)
+
 #define META_TYPE_MONITOR_MANAGER_TEST (meta_monitor_manager_test_get_type ())
 G_DECLARE_FINAL_TYPE (MetaMonitorManagerTest, meta_monitor_manager_test,
                       META, MONITOR_MANAGER_TEST, MetaMonitorManager)

src/tests/monitor-test-utils.c

@@ -529,12 +529,6 @@ check_monitor_configuration (MonitorTestCaseExpect *expect)
     }
 }
 
-static void
-meta_output_test_destroy_notify (MetaOutput *output)
-{
-  g_clear_pointer (&output->driver_private, g_free);
-}
-
 MetaMonitorTestSetup *
 create_monitor_test_setup (MonitorTestCaseSetup *setup,
                            MonitorTestFlag       flags)
@@ -627,16 +621,10 @@ create_monitor_test_setup (MonitorTestCaseSetup *setup,
                                                possible_crtc_index);
         }
 
-      output_test = g_new0 (MetaOutputTest, 1);
-
       scale = setup->outputs[i].scale;
       if (scale < 1)
         scale = 1;
 
-      *output_test = (MetaOutputTest) {
-        .scale = scale
-      };
-
       is_laptop_panel = setup->outputs[i].is_laptop_panel;
 
       serial = setup->outputs[i].serial;
@@ -679,12 +667,15 @@ create_monitor_test_setup (MonitorTestCaseSetup *setup,
       output_info->panel_orientation_transform =
         setup->outputs[i].panel_orientation_transform;
 
-      output = g_object_new (META_TYPE_OUTPUT,
+      output = g_object_new (META_TYPE_OUTPUT_TEST,
                              "id", i,
                              "gpu", test_get_gpu (),
                              "info", output_info,
                              NULL);
 
+      output_test = META_OUTPUT_TEST (output);
+      output_test->scale = scale;
+
       if (crtc)
         {
           MetaOutputAssignment output_assignment;
@@ -695,9 +686,6 @@ create_monitor_test_setup (MonitorTestCaseSetup *setup,
           meta_output_assign_crtc (output, crtc, &output_assignment);
         }
 
-      output->driver_private = output_test;
-      output->driver_notify = (GDestroyNotify) meta_output_test_destroy_notify;
-
       test_setup->outputs = g_list_append (test_setup->outputs, output);
     }