monitor-unit-tests: Add tests to verify the computed scaling values

Scaling values computation code served us well in the past years but
it's quite delicate and it has some issues in edge cases, so add a test
that verifies that the computed scaling values for all the most common
resolutions (and some that may be common in future) are what we expect
to be.

This may also serve us in future when we'd define a better algorithm to
compute the preferred scale, but this not the day.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1878>

src/tests/monitor-test-utils.c

@@ -21,6 +21,8 @@
 
 #include "tests/monitor-test-utils.h"
 
+#include <float.h>
+
 #include "backends/meta-backend-private.h"
 #include "backends/meta-crtc.h"
 #include "backends/meta-logical-monitor.h"
@@ -778,3 +780,83 @@ create_monitor_test_setup (MonitorTestCaseSetup *setup,
 
   return test_setup;
 }
+
+static void
+check_expected_scales (MetaMonitor                 *monitor,
+                       MetaMonitorMode             *monitor_mode,
+                       MetaMonitorScalesConstraint  constraints,
+                       int                          n_expected_scales,
+                       float                       *expected_scales)
+{
+  g_autofree float *scales = NULL;
+  int n_supported_scales;
+  int width, height;
+  int i;
+
+  scales = meta_monitor_calculate_supported_scales (monitor, monitor_mode,
+                                                    constraints,
+                                                    &n_supported_scales);
+  g_assert_cmpint (n_expected_scales, ==, n_supported_scales);
+
+  meta_monitor_mode_get_resolution (monitor_mode, &width, &height);
+
+  for (i = 0; i < n_supported_scales; i++)
+    {
+      g_assert_cmpfloat (scales[i], >, 0.0);
+      g_assert_cmpfloat_with_epsilon (scales[i], expected_scales[i], 0.000001);
+
+      if (!(constraints & META_MONITOR_SCALES_CONSTRAINT_NO_FRAC))
+        {
+          /* Also ensure that the scale will generate an integral resolution */
+          g_assert_cmpfloat (fmodf (width / scales[i], 1.0), ==, 0.0);
+          g_assert_cmpfloat (fmodf (height / scales[i], 1.0), ==, 0.0);
+        }
+    }
+}
+
+void check_monitor_scales (MonitorTestCaseExpect       *expect,
+                           MetaMonitorScalesConstraint  scales_constraints)
+{
+  MetaBackend *backend = meta_get_backend ();
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (backend);
+
+  GList *monitors;
+  GList *l;
+  int i;
+
+  monitors = meta_monitor_manager_get_monitors (monitor_manager);
+  g_assert_cmpuint (g_list_length (monitors), ==, expect->n_monitors);
+
+  for (l = monitors, i = 0; l; l = l->next, i++)
+    {
+      MetaMonitor *monitor = l->data;
+      MonitorTestCaseMonitor *expected_monitor = &expect->monitors[i];
+      GList *modes = meta_monitor_get_modes (monitor);
+      GList *k;
+      int j;
+
+      g_debug ("Checking monitor %d", i);
+      g_assert_cmpuint (g_list_length (modes), ==, expected_monitor->n_modes);
+
+      for (j = 0, k = modes; k; k = k->next, j++)
+        {
+          MetaMonitorMode *monitor_mode = k->data;
+          MetaMonitorTestCaseMonitorMode *expected_mode =
+            &expected_monitor->modes[j];
+          int width, height;
+
+          meta_monitor_mode_get_resolution (monitor_mode, &width, &height);
+          g_debug ("Checking %s scaling values for mode %dx%d",
+            (scales_constraints & META_MONITOR_SCALES_CONSTRAINT_NO_FRAC) ?
+            "integer" : "fractional", width, height);
+
+          g_assert_cmpint (width, ==, expected_mode->width);
+          g_assert_cmpint (height, ==, expected_mode->height);
+
+          check_expected_scales (monitor, monitor_mode, scales_constraints,
+                                 expected_mode->n_scales,
+                                 expected_mode->scales);
+        }
+    }
+}

src/tests/monitor-test-utils.h

@@ -24,13 +24,15 @@
 
 #include "tests/meta-monitor-manager-test.h"
 #include "backends/meta-crtc.h"
+#include "backends/meta-monitor.h"
 #include "backends/meta-output.h"
 
-#define MAX_N_MODES 10
+#define MAX_N_MODES 25
 #define MAX_N_OUTPUTS 10
 #define MAX_N_CRTCS 10
 #define MAX_N_MONITORS 10
 #define MAX_N_LOGICAL_MONITORS 10
+#define MAX_N_SCALES 20
 
 /*
  * The following structures are used to define test cases.
@@ -138,6 +140,8 @@ typedef struct _MonitorTestCaseMonitorMode
   int width;
   int height;
   float refresh_rate;
+  int n_scales;
+  float scales[MAX_N_SCALES];
   MetaCrtcModeFlag flags;
   MetaTestCaseMonitorCrtcMode crtc_modes[MAX_N_CRTCS];
 } MetaMonitorTestCaseMonitorMode;
@@ -199,6 +203,8 @@ void set_custom_monitor_config (const char *filename);
 char * read_file (const char *file_path);
 
 void check_monitor_configuration (MonitorTestCaseExpect *expect);
+void check_monitor_scales (MonitorTestCaseExpect       *expect,
+                           MetaMonitorScalesConstraint  scales_constraints);
 
 MetaMonitorTestSetup * create_monitor_test_setup (MonitorTestCaseSetup *setup,
                                                   MonitorTestFlag       flags);

src/tests/monitor-unit-tests.c

@@ -5727,6 +5727,316 @@ meta_test_monitor_migrated_wiggle (void)
     g_error ("Failed to remove test data output file: %s", error->message);
 }
 
+static void
+meta_test_monitor_supported_fractional_scales (void)
+{
+  MonitorTestCase test_case = {
+    .setup = {
+      .n_modes = 21,
+      .modes = {
+        {
+          .width = 800,
+          .height = 600,
+          .refresh_rate = 60.0
+        },
+        {
+          .width = 1024,
+          .height = 768,
+          .refresh_rate = 60.0
+        },
+        {
+          .width = 1280,
+          .height = 720,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1280,
+          .height = 800,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1280,
+          .height = 1024,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1366,
+          .height = 768,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1440,
+          .height = 900,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1400,
+          .height = 1050,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1600,
+          .height = 900,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1920,
+          .height = 1080,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 1920,
+          .height = 1200,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 2650,
+          .height = 1440,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 2880,
+          .height = 1800,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 3200,
+          .height = 1800,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 3200,
+          .height = 2048,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 3840,
+          .height = 2160,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 3840,
+          .height = 2400,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 4096,
+          .height = 2160,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 4096,
+          .height = 3072,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 5120,
+          .height = 2880,
+          .refresh_rate = 60.0,
+        },
+        {
+          .width = 7680,
+          .height = 4320,
+          .refresh_rate = 60.0,
+        },
+      },
+      .outputs = {
+        {
+          .crtc = -1,
+          .modes = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
+                     17, 18, 19, 20 },
+          .n_modes = 21,
+          .preferred_mode = 5,
+          .possible_crtcs = { 0 },
+          .n_possible_crtcs = 1,
+          .width_mm = 222,
+          .height_mm = 125
+        }
+      },
+      .n_outputs = 1,
+      .crtcs = {
+        {
+          .current_mode = 0
+        }
+      },
+      .n_crtcs = 1
+    },
+
+    .expect = {
+      .n_monitors = 1,
+      .monitors = {
+        {
+          .n_modes = 21,
+          .modes = {
+            {
+              .width = 800,
+              .height = 600,
+              .n_scales = 1,
+              .scales = { 1.000000 },
+            },
+            {
+              .width = 1024,
+              .height = 768,
+              .n_scales = 2,
+              .scales = { 1.000000, 1.24878049 },
+            },
+            {
+              .width = 1280,
+              .height = 720,
+              .n_scales = 3,
+              .scales = { 1.000000, 1.250000, 1.509434 },
+            },
+            {
+              .width = 1280,
+              .height = 800,
+              .n_scales = 3,
+              .scales = { 1.000000, 1.250000, 1.495327 },
+            },
+            {
+              .width = 1280,
+              .height = 1024,
+              .n_scales = 4,
+              .scales = { 1.000000, 1.248780, 1.497076, 1.753425 },
+            },
+            {
+              .width = 1366,
+              .height = 768,
+              .n_scales = 1,
+              .scales = { 1.000000 },
+            },
+            {
+              .width = 1440,
+              .height = 900,
+              .n_scales = 4,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.747573 },
+            },
+            {
+              .width = 1400,
+              .height = 1050,
+              .n_scales = 4,
+              .scales = { 1.000000, 1.250000, 1.502146, 1.750000 },
+            },
+            {
+              .width = 1600,
+              .height = 900,
+              .n_scales = 4,
+              .scales = { 1.000000, 1.250000, 1.492537, 1.754386 },
+            },
+            {
+              .width = 1920,
+              .height = 1080,
+              .n_scales = 6,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.739130, 2.000000,
+                          2.307692 },
+            },
+            {
+              .width = 1920,
+              .height = 1200,
+              .n_scales = 6,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.751825, 2.000000,
+                          2.242991 },
+            },
+            {
+              .width = 2650,
+              .height = 1440,
+              .n_scales = 6,
+              .scales = { 1.000000, 1.250000, 1.428571, 1.666667, 2.000000,
+                          2.500000
+              },
+            },
+            {
+              .width = 2880,
+              .height = 1800,
+              .n_scales = 11,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.747573, 2.000000,
+                          2.250000, 2.500000, 2.748092, 3.000000, 3.243243,
+                          3.495146
+              },
+            },
+            {
+              .width = 3200,
+              .height = 1800,
+              .n_scales = 12,
+              .scales = { 1.000000, 1.250000, 1.503759, 1.754386, 2.000000,
+                          2.247191, 2.500000, 2.739726, 2.985075, 3.225806,
+                          3.508772, 3.773585
+              },
+            },
+            {
+              .width = 3200,
+              .height = 2048,
+              .n_scales = 13,
+              .scales = { 1.000000, 1.254902, 1.505882, 1.753425, 2.000000,
+                          2.245614, 2.509804, 2.723404, 2.976744, 3.282051,
+                          3.459460, 3.764706, 4.000000,
+              },
+            },
+            {
+              .width = 3840,
+              .height = 2160,
+              .n_scales = 13,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.751825, 2.000000,
+                          2.201835, 2.500000, 2.758621, 3.000000, 3.243243,
+                          3.478261, 3.750000, 4.000000
+              },
+            },
+            {
+              .width = 3840,
+              .height = 2400,
+              .n_scales = 13,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.751825, 2.000000,
+                          2.253521, 2.500000, 2.742857, 3.000000, 3.243243,
+                          3.503650, 3.750000, 4.000000
+              },
+            },
+            {
+              .width = 4096,
+              .height = 2160,
+              .n_scales = 10,
+              .scales = { 1.000000, 1.333333, 1.454545, 1.777778, 2.000000,
+                          2.666667, 2.666667, 3.200000, 3.200000, 4.000000
+              }
+            },
+            {
+              .width = 4096,
+              .height = 3072,
+              .n_scales = 13,
+              .scales = { 1.000000, 1.250305, 1.499268, 1.750427, 2.000000,
+                          2.245614, 2.497561, 2.752688, 3.002933, 3.250794,
+                          3.494880, 3.750916, 4.000000
+              },
+            },
+            {
+              .width = 5120,
+              .height = 2880,
+              .n_scales = 13,
+              .scales = { 1.000000, 1.250000, 1.495327, 1.748634, 2.000000,
+                          2.253521, 2.500000, 2.758621, 2.990654, 3.265306,
+                          3.516484, 3.764706, 4.000000
+              },
+            },
+            {
+              .width = 7680,
+              .height = 4320,
+              .n_scales = 13,
+              .scales = { 1.000000, 1.250000, 1.500000, 1.751825, 2.000000,
+                          2.211982, 2.500000, 2.742857, 3.000000, 3.243243,
+                          3.503650, 3.750000, 4.000000
+              },
+            },
+          },
+        },
+      },
+    },
+  };
+
+  MetaMonitorTestSetup *test_setup;
+  test_setup = create_monitor_test_setup (&test_case.setup,
+                                          MONITOR_TEST_FLAG_NO_STORED);
+  emulate_hotplug (test_setup);
+  check_monitor_scales (&test_case.expect, META_MONITOR_SCALES_CONSTRAINT_NONE);
+}
+
 static void
 test_case_setup (void       **fixture,
                  const void   *data)
@@ -5853,6 +6163,9 @@ init_monitor_tests (void)
 
   add_monitor_test ("/backends/monitor/wm/tiling",
                     meta_test_monitor_wm_tiling);
+
+  add_monitor_test ("/backends/monitor/suppported_scales/fractional",
+                    meta_test_monitor_supported_fractional_scales);
 }
 
 void