backends/input-mapper: Implement score mechanism to assign the most relevant output

We used to pick the "best" output for each builtin/size/edid categories,
and then pick the "best" (in that order) of those for each input device.
This is most often enough, but is prone to wrong results in some corner
cases (eg. 2 outputs with the exact same dimensions).

Change this to a score mechanism that doesn't leave outputs out. The
weights are the same, but the score is accumulated if an output matches
multiple categories. All outputs are evaluated and sorted by score, and
input devices with the best matches are applied first (as they already
did).

This should break the tie if eg. there's 2 outputs with similar dimensions,
but one of them has some EDID match in addition. The output with multiple
matches will score higher up, while it might have been entirely discarded
with the previous implementation.

Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/1175

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1202

src/backends/meta-input-mapper.c

@@ -35,6 +35,7 @@ typedef struct _MetaMapperInputInfo MetaMapperInputInfo;
 typedef struct _MetaMapperOutputInfo MetaMapperOutputInfo;
 typedef struct _MappingHelper MappingHelper;
 typedef struct _DeviceCandidates DeviceCandidates;
+typedef struct _DeviceMatch DeviceMatch;
 
 struct _MetaInputMapper
 {
@@ -59,11 +60,11 @@ typedef enum
 
 typedef enum
 {
-  META_MATCH_IS_BUILTIN,   /* Output is builtin, applies mainly to system-integrated devices */
-  META_MATCH_SIZE,         /* Size from input device and output match */
-  META_MATCH_EDID_FULL,    /* Full EDID model match, eg. "Cintiq 12WX" */
-  META_MATCH_EDID_PARTIAL, /* Partial EDID model match, eg. "Cintiq" */
   META_MATCH_EDID_VENDOR,  /* EDID vendor match, eg. "WAC" for Wacom */
+  META_MATCH_EDID_PARTIAL, /* Partial EDID model match, eg. "Cintiq" */
+  META_MATCH_EDID_FULL,    /* Full EDID model match, eg. "Cintiq 12WX" */
+  META_MATCH_SIZE,         /* Size from input device and output match */
+  META_MATCH_IS_BUILTIN,   /* Output is builtin, applies mainly to system-integrated devices */
   N_OUTPUT_MATCHES
 } MetaOutputMatchType;
 
@@ -87,13 +88,19 @@ struct _MappingHelper
   GArray *device_maps;
 };
 
+struct _DeviceMatch
+{
+  MetaMonitor *monitor;
+  uint32_t score;
+};
+
 struct _DeviceCandidates
 {
   MetaMapperInputInfo *input;
 
-  MetaMonitor *candidates[N_OUTPUT_MATCHES];
+  GArray *matches; /* Array of DeviceMatch */
 
-  MetaOutputMatchType best;
+  int best;
 };
 
 enum
@@ -227,10 +234,18 @@ mapper_output_info_clear_inputs (MetaMapperOutputInfo *output)
   output->attached_caps = 0;
 }
 
+static void
+clear_candidates (DeviceCandidates *candidates)
+{
+  g_clear_pointer (&candidates->matches, g_array_unref);
+}
+
 static void
 mapping_helper_init (MappingHelper *helper)
 {
   helper->device_maps = g_array_new (FALSE, FALSE, sizeof (DeviceCandidates));
+  g_array_set_clear_func (helper->device_maps,
+                          (GDestroyNotify) clear_candidates);
 }
 
 static void
@@ -305,52 +320,37 @@ input_device_get_physical_size (MetaInputMapper    *mapper,
 }
 
 static gboolean
-find_size_match (MetaMapperInputInfo  *input,
+match_size (MetaMapperInputInfo  *input,
-                 GList                *monitors,
+            MetaMonitor          *monitor)
-                 MetaMonitor         **matched_monitor)
 {
-  double min_w_diff, min_h_diff;
+  double w_diff, h_diff;
+  int o_width, o_height;
   double i_width, i_height;
-  gboolean found = FALSE;
-  GList *l;
-
-  min_w_diff = min_h_diff = MAX_SIZE_MATCH_DIFF;
 
   if (!input_device_get_physical_size (input->mapper, input->device,
                                        &i_width, &i_height))
     return FALSE;
 
-  for (l = monitors; l; l = l->next)
-    {
-      MetaMonitor *monitor = l->data;
-      double w_diff, h_diff;
-      int o_width, o_height;
 
-      meta_monitor_get_physical_dimensions (monitor, &o_width, &o_height);
+  meta_monitor_get_physical_dimensions (monitor, &o_width, &o_height);
-      w_diff = ABS (1 - ((double) o_width / i_width));
+  w_diff = ABS (1 - ((double) o_width / i_width));
-      h_diff = ABS (1 - ((double) o_height / i_height));
+  h_diff = ABS (1 - ((double) o_height / i_height));
 
-      if (w_diff >= min_w_diff || h_diff >= min_h_diff)
+  return w_diff < MAX_SIZE_MATCH_DIFF && h_diff < MAX_SIZE_MATCH_DIFF;
-        continue;
-
-      *matched_monitor = monitor;
-      min_w_diff = w_diff;
-      min_h_diff = h_diff;
-      found = TRUE;
-    }
-
-  return found;
 }
 
 static gboolean
-find_builtin_output (MetaInputMapper  *mapper,
+match_builtin (MetaInputMapper *mapper,
-                     MetaMonitor     **matched_monitor)
+               MetaMonitor     *monitor)
 {
-  MetaMonitor *panel;
+  return monitor == meta_monitor_manager_get_laptop_panel (mapper->monitor_manager);
+}
 
-  panel = meta_monitor_manager_get_laptop_panel (mapper->monitor_manager);
+static int
-  *matched_monitor = panel;
+sort_by_score (DeviceMatch *match1,
-  return panel != NULL;
+               DeviceMatch *match2)
+{
+  return (int) match1->score - match2->score;
 }
 
 static void
@@ -358,36 +358,45 @@ guess_candidates (MetaInputMapper     *mapper,
                   MetaMapperInputInfo *input,
                   DeviceCandidates    *info)
 {
-  MetaOutputMatchType best = N_OUTPUT_MATCHES;
   GList *monitors, *l;
-  MetaMonitor *matched_monitor = NULL;
 
   monitors = meta_monitor_manager_get_monitors (mapper->monitor_manager);
 
   for (l = monitors; l; l = l->next)
     {
       MetaOutputMatchType edid_match;
+      DeviceMatch match = { l->data, 0 };
 
       if (match_edid (input, l->data, &edid_match))
-        {
+        match.score |= 1 << edid_match;
-          best = MIN (best, edid_match);
+
-          info->candidates[edid_match] = l->data;
+      if (match_size (input, l->data))
-        }
+        match.score |= 1 << META_MATCH_SIZE;
+
+      if (input->builtin && match_builtin (mapper, l->data))
+        match.score |= 1 << META_MATCH_IS_BUILTIN;
+
+      if (match.score > 0)
+        g_array_append_val (info->matches, match);
     }
 
-  if (find_size_match (input, monitors, &matched_monitor))
+  if (info->matches->len == 0)
     {
-      best = MIN (best, META_MATCH_SIZE);
+      DeviceMatch match = { 0 };
-      info->candidates[META_MATCH_SIZE] = matched_monitor;
-    }
 
-  if (input->builtin || best == N_OUTPUT_MATCHES)
+      match.monitor =
+        meta_monitor_manager_get_laptop_panel (mapper->monitor_manager);
+      g_array_append_val (info->matches, match);
+      info->best = 0;
+    }
+  else
     {
-      best = MIN (best, META_MATCH_IS_BUILTIN);
+      DeviceMatch *best;
-      find_builtin_output (mapper, &info->candidates[META_MATCH_IS_BUILTIN]);
-    }
 
-  info->best = best;
+      g_array_sort (info->matches, (GCompareFunc) sort_by_score);
+      best = &g_array_index (info->matches, DeviceMatch, 0);
+      info->best = best->score;
+    }
 }
 
 static void
@@ -399,6 +408,7 @@ mapping_helper_add (MappingHelper       *helper,
   guint i, pos = 0;
 
   info.input = input;
+  info.matches = g_array_new (FALSE, TRUE, sizeof (DeviceMatch));
 
   guess_candidates (mapper, input, &info);
 
@@ -408,7 +418,7 @@ mapping_helper_add (MappingHelper       *helper,
 
       elem = &g_array_index (helper->device_maps, DeviceCandidates, i);
 
-      if (elem->best < info.best)
+      if (elem->best > info.best)
         pos = i;
     }
 
@@ -422,26 +432,25 @@ static void
 mapping_helper_apply (MappingHelper   *helper,
                       MetaInputMapper *mapper)
 {
-  guint i;
+  guint i, j;
 
   /* Now, decide which input claims which output */
   for (i = 0; i < helper->device_maps->len; i++)
     {
-      MetaMapperOutputInfo *output;
       DeviceCandidates *info;
-      MetaOutputMatchType j;
 
       info = &g_array_index (helper->device_maps, DeviceCandidates, i);
 
-      for (j = 0; j < N_OUTPUT_MATCHES; j++)
+      for (j = 0; j < info->matches->len; j++)
         {
           MetaLogicalMonitor *logical_monitor;
+          MetaMapperOutputInfo *output;
+          MetaMonitor *monitor;
+          DeviceMatch *match;
 
-          if (!info->candidates[j])
+          match = &g_array_index (info->matches, DeviceMatch, j);
-            continue;
+          monitor = match->monitor;
-
+          logical_monitor = meta_monitor_get_logical_monitor (monitor);
-          logical_monitor =
-            meta_monitor_get_logical_monitor (info->candidates[j]);
           output = g_hash_table_lookup (mapper->output_devices,
                                         logical_monitor);
 
@@ -451,8 +460,7 @@ mapping_helper_apply (MappingHelper   *helper,
           if (output->attached_caps & mapper_input_info_get_caps (info->input))
             continue;
 
-          mapper_output_info_add_input (output, info->input,
+          mapper_output_info_add_input (output, info->input, monitor);
-                                        info->candidates[j]);
           break;
         }
     }