monitor-manager-xrandr: Use monitor to calculate scaling

In Xrandr we were caching the available scaling modes that were computed just
for the current mode, for each monitor, while we can actually reuse the
default implementation, by just passing the proper scaling constraint.

In monitor we need then to properly filter these values, by only accepting
integer scaling factors that would allow to have a minimal logical monitor
size.

Fixes https://gitlab.gnome.org/GNOME/mutter/issues/407

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/336>

src/backends/meta-monitor.c

@@ -1737,6 +1737,18 @@ is_logical_size_large_enough (int width,
   return width * height >= MINIMUM_LOGICAL_AREA;
 }
 
+static gboolean
+is_scale_valid_for_size (float width,
+                         float height,
+                         float scale)
+{
+  if (scale < MINIMUM_SCALE_FACTOR || scale > MAXIMUM_SCALE_FACTOR)
+    return FALSE;
+
+  return is_logical_size_large_enough (floorf (width / scale),
+                                       floorf (height / scale));
+}
+
 gboolean
 meta_monitor_mode_should_be_advertised (MetaMonitorMode *monitor_mode)
 {
@@ -1766,20 +1778,16 @@ get_closest_scale_factor_for_resolution (float width,
   gboolean found_one;
 
   best_scale = 0;
-  scaled_w = width / scale;
-  scaled_h = height / scale;
 
-  if (scale < MINIMUM_SCALE_FACTOR ||
+  if (!is_scale_valid_for_size (width, height, scale))
-      scale > MAXIMUM_SCALE_FACTOR ||
-      !is_logical_size_large_enough (floorf (scaled_w), floorf (scaled_h)))
     goto out;
 
-  if (floorf (scaled_w) == scaled_w && floorf (scaled_h) == scaled_h)
+  if (fmodf (width, scale) == 0.0 && fmodf (height, scale) == 0.0)
     return scale;
 
   i = 0;
   found_one = FALSE;
-  base_scaled_w = floorf (scaled_w);
+  base_scaled_w = floorf (width / scale);
 
   do
     {
@@ -1840,15 +1848,20 @@ meta_monitor_calculate_supported_scales (MetaMonitor                 *monitor,
           float scale;
           float scale_value = i + j * SCALE_FACTORS_STEPS;
 
-          if ((constraints & META_MONITOR_SCALES_CONSTRAINT_NO_FRAC) &&
+          if (constraints & META_MONITOR_SCALES_CONSTRAINT_NO_FRAC)
-              fmodf (scale_value, 1.0) != 0.0)
             {
+              if (fmodf (scale_value, 1.0) != 0.0 ||
+                  !is_scale_valid_for_size (width, height, scale_value))
                 continue;
-            }
 
+              scale = scale_value;
+            }
+          else
+            {
               scale = get_closest_scale_factor_for_resolution (width,
                                                                height,
                                                                scale_value);
+            }
 
           if (scale > 0.0f)
             g_array_append_val (supported_scales, scale);

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

@@ -77,9 +77,6 @@ struct _MetaMonitorManagerXrandr
   xcb_timestamp_t last_xrandr_set_timestamp;
 
   GHashTable *tiled_monitor_atoms;
-
-  float *supported_scales;
-  int n_supported_scales;
 };
 
 struct _MetaMonitorManagerXrandrClass
@@ -584,17 +581,6 @@ meta_monitor_manager_xrandr_ensure_initial_config (MetaMonitorManager *manager)
   meta_monitor_manager_update_logical_state_derived (manager, config);
 }
 
-static void
-meta_monitor_manager_xrandr_rebuild_derived (MetaMonitorManager *manager,
-                                             MetaMonitorsConfig *config)
-{
-  MetaMonitorManagerXrandr *manager_xrandr =
-    META_MONITOR_MANAGER_XRANDR (manager);
-
-  g_clear_pointer (&manager_xrandr->supported_scales, g_free);
-  meta_monitor_manager_rebuild_derived (manager, config);
-}
-
 static gboolean
 meta_monitor_manager_xrandr_apply_monitors_config (MetaMonitorManager      *manager,
                                                    MetaMonitorsConfig      *config,
@@ -609,7 +595,7 @@ meta_monitor_manager_xrandr_apply_monitors_config (MetaMonitorManager      *mana
       if (!manager->in_init)
         apply_crtc_assignments (manager, TRUE, NULL, 0, NULL, 0);
 
-      meta_monitor_manager_xrandr_rebuild_derived (manager, NULL);
+      meta_monitor_manager_rebuild_derived (manager, NULL);
       return TRUE;
     }
 
@@ -644,7 +630,7 @@ meta_monitor_manager_xrandr_apply_monitors_config (MetaMonitorManager      *mana
         }
       else
         {
-          meta_monitor_manager_xrandr_rebuild_derived (manager, config);
+          meta_monitor_manager_rebuild_derived (manager, config);
         }
     }
 
@@ -891,77 +877,6 @@ meta_monitor_manager_xrandr_calculate_monitor_mode_scale (MetaMonitorManager
   return meta_monitor_calculate_mode_scale (monitor, monitor_mode, constraints);
 }
 
-static void
-add_supported_scale (GArray *supported_scales,
-                     float   scale)
-{
-  unsigned int i;
-
-  for (i = 0; i < supported_scales->len; i++)
-    {
-      float supported_scale = g_array_index (supported_scales, float, i);
-
-      if (scale == supported_scale)
-        return;
-    }
-
-  g_array_append_val (supported_scales, scale);
-}
-
-static int
-compare_scales (gconstpointer a,
-                gconstpointer b)
-{
-  float f = *(float *) a - *(float *) b;
-
-  if (f < 0)
-    return -1;
-  if (f > 0)
-    return 1;
-  return 0;
-}
-
-static void
-ensure_supported_monitor_scales (MetaMonitorManager *manager)
-{
-  MetaMonitorManagerXrandr *manager_xrandr =
-    META_MONITOR_MANAGER_XRANDR (manager);
-  MetaMonitorScalesConstraint constraints;
-  GList *l;
-  GArray *supported_scales;
-
-  if (manager_xrandr->supported_scales)
-    return;
-
-  constraints = META_MONITOR_SCALES_CONSTRAINT_NO_FRAC;
-  supported_scales = g_array_new (FALSE, FALSE, sizeof (float));
-
-  for (l = manager->monitors; l; l = l->next)
-    {
-      MetaMonitor *monitor = l->data;
-      MetaMonitorMode *monitor_mode;
-      float *monitor_scales;
-      int n_monitor_scales;
-      int i;
-
-      monitor_mode = meta_monitor_get_preferred_mode (monitor);
-      monitor_scales =
-        meta_monitor_calculate_supported_scales (monitor,
-                                                 monitor_mode,
-                                                 constraints,
-                                                 &n_monitor_scales);
-
-      for (i = 0; i < n_monitor_scales; i++)
-        add_supported_scale (supported_scales, monitor_scales[i]);
-      g_array_sort (supported_scales, compare_scales);
-      g_free (monitor_scales);
-    }
-
-  manager_xrandr->supported_scales = (float *) supported_scales->data;
-  manager_xrandr->n_supported_scales = supported_scales->len;
-  g_array_free (supported_scales, FALSE);
-}
-
 static float *
 meta_monitor_manager_xrandr_calculate_supported_scales (MetaMonitorManager           *manager,
                                                         MetaLogicalMonitorLayoutMode  layout_mode,
@@ -969,14 +884,12 @@ meta_monitor_manager_xrandr_calculate_supported_scales (MetaMonitorManager
                                                         MetaMonitorMode              *monitor_mode,
                                                         int                          *n_supported_scales)
 {
-  MetaMonitorManagerXrandr *manager_xrandr =
+  MetaMonitorScalesConstraint constraints;
-    META_MONITOR_MANAGER_XRANDR (manager);
 
-  ensure_supported_monitor_scales (manager);
+  constraints = META_MONITOR_SCALES_CONSTRAINT_NO_FRAC;
-
+  return meta_monitor_calculate_supported_scales (monitor, monitor_mode,
-  *n_supported_scales = manager_xrandr->n_supported_scales;
+                                                  constraints,
-  return g_memdup2 (manager_xrandr->supported_scales,
+                                                  n_supported_scales);
-                    manager_xrandr->n_supported_scales * sizeof (float));
 }
 
 static MetaMonitorManagerCapability
@@ -1063,7 +976,6 @@ meta_monitor_manager_xrandr_finalize (GObject *object)
   MetaMonitorManagerXrandr *manager_xrandr = META_MONITOR_MANAGER_XRANDR (object);
 
   g_hash_table_destroy (manager_xrandr->tiled_monitor_atoms);
-  g_free (manager_xrandr->supported_scales);
 
   G_OBJECT_CLASS (meta_monitor_manager_xrandr_parent_class)->finalize (object);
 }
@@ -1148,7 +1060,7 @@ meta_monitor_manager_xrandr_handle_xevent (MetaMonitorManagerXrandr *manager_xra
           config = NULL;
         }
 
-      meta_monitor_manager_xrandr_rebuild_derived (manager, config);
+      meta_monitor_manager_rebuild_derived (manager, config);
     }
 
   return TRUE;