monitor: Add mode spec helper checking resolution similarness

If two modes are roughly the same, they should probably use the same UI
scaling factor. I.e. for the same monitor, if a 4K mode was configured to
have a certain scaling factor, and we generate a new configuration with
a similar sized 4K mode, we should re-use the scale previously
configured; however if we e.g. go from a 4K mode to a FHD mode, we
shouldn't.

This allows implementing better hueristics when using the switch-config
feature, where we'd be less likely to loose the for a certain monitor
mode combination previously configured scaling factor.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2479>

src/tests/meson.build

@@ -195,6 +195,11 @@ test_cases += [
     'suite': 'backend',
     'sources': [ 'monitor-unit-tests.c', ],
   },
+  {
+    'name': 'monitor-utils',
+    'suite': 'unit',
+    'sources': [ 'monitor-util-tests.c', ],
+  },
   {
     'name': 'headless-start',
     'suite': 'backend',

src/tests/monitor-util-tests.c

@@ -0,0 +1,143 @@
+/*
+ * Copyright (C) 2022 Red Hat
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ *
+ */
+
+#include "config.h"
+
+#include "backends/meta-monitor.h"
+
+static void
+assert_matches_none (MetaMonitorModeSpec *mode_spec,
+                     MetaMonitorModeSpec *mode_specs,
+                     int                  n_mode_specs)
+{
+  int i;
+
+  for (i = 0; i < n_mode_specs; i++)
+    {
+      g_assert_false (meta_monitor_mode_spec_has_similar_size (mode_spec,
+                                                               &mode_specs[i]));
+    }
+}
+
+static void
+meta_test_monitor_mode_spec_similar_size (void)
+{
+  MetaMonitorModeSpec matching_4k_specs[] = {
+    { .width = 4096, .height = 2560 }, /* 16:10 */
+    { .width = 4096, .height = 2304 }, /* 16:9 */
+    { .width = 3840, .height = 2400 }, /* 16:10 */
+    { .width = 3840, .height = 2160 }, /* 16:9 */
+  };
+  MetaMonitorModeSpec matching_uhd_specs[] = {
+    { .width = 1920, .height = 1200 }, /* 16:10 */
+    { .width = 1920, .height = 1080 }, /* 16:9 */
+    { .width = 2048, .height = 1152 }, /* 16:9 */
+  };
+  MetaMonitorModeSpec matching_hd_specs[] = {
+    { .width = 1366, .height = 768 }, /* ~16:9 */
+    { .width = 1280, .height = 720 }, /* 16:9 */
+  };
+  MetaMonitorModeSpec nonmatching_specs[] = {
+    { .width = 1024, .height = 768 },
+    { .width = 800, .height = 600 },
+    { .width = 640, .height = 480 },
+  };
+  int i;
+
+  /* Test that 4K modes only matches other 4K modes */
+
+  for (i = 0; i < G_N_ELEMENTS (matching_4k_specs); i++)
+    {
+      MetaMonitorModeSpec *mode_spec = &matching_4k_specs[i];
+      MetaMonitorModeSpec *prev_mode_spec = &matching_4k_specs[i - 1];
+
+      if (i != 0)
+        {
+          g_assert_true (meta_monitor_mode_spec_has_similar_size (mode_spec,
+                                                                  prev_mode_spec));
+        }
+
+      assert_matches_none (mode_spec,
+                           matching_uhd_specs, G_N_ELEMENTS (matching_uhd_specs));
+      assert_matches_none (mode_spec,
+                           matching_hd_specs, G_N_ELEMENTS (matching_hd_specs));
+      assert_matches_none (mode_spec,
+                           nonmatching_specs, G_N_ELEMENTS (nonmatching_specs));
+    }
+
+  /* Test that FHD modes only matches other FHD modes */
+
+  for (i = 0; i < G_N_ELEMENTS (matching_uhd_specs); i++)
+    {
+      MetaMonitorModeSpec *mode_spec = &matching_uhd_specs[i];
+      MetaMonitorModeSpec *prev_mode_spec = &matching_uhd_specs[i - 1];
+
+      if (i != 0)
+        {
+          g_assert_true (meta_monitor_mode_spec_has_similar_size (mode_spec,
+                                                                  prev_mode_spec));
+        }
+
+      assert_matches_none (mode_spec,
+                           matching_hd_specs, G_N_ELEMENTS (matching_hd_specs));
+      assert_matches_none (mode_spec,
+                           nonmatching_specs, G_N_ELEMENTS (nonmatching_specs));
+    }
+
+  /* Test that HD modes only matches other HD modes */
+
+  for (i = 0; i < G_N_ELEMENTS (matching_hd_specs); i++)
+    {
+      MetaMonitorModeSpec *mode_spec = &matching_hd_specs[i];
+      MetaMonitorModeSpec *prev_mode_spec = &matching_hd_specs[i - 1];
+
+      if (i != 0)
+        {
+          g_assert_true (meta_monitor_mode_spec_has_similar_size (mode_spec,
+                                                                  prev_mode_spec));
+        }
+
+      assert_matches_none (mode_spec,
+                           nonmatching_specs, G_N_ELEMENTS (nonmatching_specs));
+    }
+
+  /* Test that the other modes doesn't match each other. */
+
+  for (i = 0; i < G_N_ELEMENTS (nonmatching_specs) - 1; i++)
+    {
+      MetaMonitorModeSpec *mode_spec = &nonmatching_specs[i];
+      MetaMonitorModeSpec *next_mode_spec = &nonmatching_specs[i + 1];
+
+      g_assert_false (meta_monitor_mode_spec_has_similar_size (mode_spec,
+                                                               next_mode_spec));
+    }
+}
+
+int
+main (int    argc,
+      char **argv)
+{
+  g_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/backends/monitor/spec/similar-size",
+                   meta_test_monitor_mode_spec_similar_size);
+
+  return g_test_run ();
+}