Linux: Use a hash table to map cursors (flutter#19561)

Refactors the process of looking up system mouse cursor value, so that instead of a linear search it uses a hash table.

shell/platform/linux/fl_mouse_cursor_plugin.cc

@@ -14,16 +14,47 @@ static constexpr char kBadArgumentsError[] = "Bad Arguments";
 static constexpr char kActivateSystemCursorMethod[] = "activateSystemCursor";
 static constexpr char kKindKey[] = "kind";
 
+static constexpr char kFallbackCursor[] = "default";
+
 struct _FlMouseCursorPlugin {
   GObject parent_instance;
 
   FlMethodChannel* channel;
 
   FlView* view;
+
+  GHashTable* system_cursor_table;
 };
 
 G_DEFINE_TYPE(FlMouseCursorPlugin, fl_mouse_cursor_plugin, G_TYPE_OBJECT)
 
+// Insert a new entry into a hashtable from strings to strings.
+//
+// Returns whether the newly added value was already in the hash table or not.
+static bool define_system_cursor(GHashTable* table,
+                                 const gchar* key,
+                                 const gchar* value) {
+  return g_hash_table_insert(
+      table, reinterpret_cast<gpointer>(const_cast<gchar*>(key)),
+      reinterpret_cast<gpointer>(const_cast<gchar*>(value)));
+}
+
+// Populate the hash table so that it maps from Flutter's cursor kinds to GTK's
+// cursor values.
+//
+// The table must have been created as a hashtable from strings to strings.
+static void populate_system_cursor_table(GHashTable* table) {
+  // The following mapping must be kept in sync with Flutter framework's
+  // mouse_cursor.dart.
+  define_system_cursor(table, "none", "none");
+  define_system_cursor(table, "click", "pointer");
+  define_system_cursor(table, "text", "text");
+  define_system_cursor(table, "forbidden", "not-allowed");
+  define_system_cursor(table, "grab", "grabbing");
+  define_system_cursor(table, "resizeLeftRight", "ew-resize");
+  define_system_cursor(table, "resizeUpDown", "ns-resize");
+}
+
 // Sets the mouse cursor.
 FlMethodResponse* activate_system_cursor(FlMouseCursorPlugin* self,
                                          FlValue* args) {
@@ -37,27 +68,15 @@ FlMethodResponse* activate_system_cursor(FlMouseCursorPlugin* self,
   if (fl_value_get_type(kind_value) == FL_VALUE_TYPE_STRING)
     kind = fl_value_get_string(kind_value);
 
-  const gchar* cursor_name = nullptr;
-  if (g_strcmp0(kind, "none") == 0)
-    cursor_name = "none";
-  else if (g_strcmp0(kind, "basic") == 0)
-    cursor_name = "default";
-  else if (g_strcmp0(kind, "click") == 0)
-    cursor_name = "pointer";
-  else if (g_strcmp0(kind, "text") == 0)
-    cursor_name = "text";
-  else if (g_strcmp0(kind, "forbidden") == 0)
-    cursor_name = "not-allowed";
-  else if (g_strcmp0(kind, "grab") == 0)
-    cursor_name = "grab";
-  else if (g_strcmp0(kind, "grabbing") == 0)
-    cursor_name = "grabbing";
-  else if (g_strcmp0(kind, "resizeLeftRight") == 0)
-    cursor_name = "ew-resize";
-  else if (g_strcmp0(kind, "resizeUpDown") == 0)
-    cursor_name = "ns-resize";
-  else
-    cursor_name = "default";
+  if (self->system_cursor_table == nullptr) {
+    self->system_cursor_table = g_hash_table_new(g_str_hash, g_str_equal);
+    populate_system_cursor_table(self->system_cursor_table);
+  }
+
+  const gchar* cursor_name = reinterpret_cast<const gchar*>(
+      g_hash_table_lookup(self->system_cursor_table, kind));
+  if (cursor_name == nullptr)
+    cursor_name = kFallbackCursor;
 
   GdkWindow* window =
       gtk_widget_get_window(gtk_widget_get_toplevel(GTK_WIDGET(self->view)));
@@ -102,6 +121,8 @@ static void fl_mouse_cursor_plugin_dispose(GObject* object) {
     self->view = nullptr;
   }
 
+  g_clear_pointer(&self->system_cursor_table, g_hash_table_unref);
+
   G_OBJECT_CLASS(fl_mouse_cursor_plugin_parent_class)->dispose(object);
 }