diff --git a/v5/desktop.py b/v5/desktop.py
index 394269a..efd21bb 100644
--- a/v5/desktop.py
+++ b/v5/desktop.py
@@ -48,3 +48,5 @@ def desktop_createSelectedTiles(p):
     tile.top = pos[1]
     # Invisible by default.
     tile.visible = False
+  #}
+#}
diff --git a/v5/desktop_Platform.py b/v5/desktop_Platform.py
index 62b76e9..e4f6143 100644
--- a/v5/desktop_Platform.py
+++ b/v5/desktop_Platform.py
@@ -3,7 +3,9 @@ import arcade
 class desktop_Platform:
   def __init__(self):
     self.c = None
+    self.ctrl = None
     self.deselectedTiles = []
+    self.mousePosition = []
     self.selectedTiles = []
     self.sprites = arcade.SpriteList()
     self.textures = []
diff --git a/v5/desktop_Window.py b/v5/desktop_Window.py
index 4bf4c77..7ca0ebd 100644
--- a/v5/desktop_Window.py
+++ b/v5/desktop_Window.py
@@ -1,4 +1,5 @@
 import arcade
+from desktop_aux import *
 
 class desktop_Window(arcade.Window):
   def __init__(self, p):
@@ -16,10 +17,11 @@ class desktop_Window(arcade.Window):
     self.p.sprites.draw()
 
   def on_mouse_press(self, x, y, button, key_modifiers):
-    print("click", x, y)
-    sprites = arcade.get_sprites_at_point([x, y], self.p.sprites)
-    id = sprites[0].guid
-    print("selected id: ", id)
+    id = desktop_aux_tileIdAt(self.p, x, y)
+    if (
+      id != None
+    ):
+      self.p.ctrl.set("selectedId", id)
 
   def on_update(self, delta):
     self.p.sprites.update_animation()
diff --git a/v5/desktop_aux.py b/v5/desktop_aux.py
new file mode 100644
index 0000000..17bbe97
--- /dev/null
+++ b/v5/desktop_aux.py
@@ -0,0 +1,12 @@
+import arcade
+
+# Find tile id at the specified location
+def desktop_aux_tileIdAt(p, x, y):
+  sprites = arcade.get_sprites_at_point([x, y], p.sprites)
+  if (
+    len(sprites) != 0
+  ):
+    return sprites[0].guid
+  #}
+  return None
+#}
diff --git a/v5/main-gui.py b/v5/main-gui.py
index 5fcd3ba..310776a 100644
--- a/v5/main-gui.py
+++ b/v5/main-gui.py
@@ -81,6 +81,8 @@ ctrl.registerCallback(printOutput)
 ctrl.registerFieldCallback("exit", lambda c: sys.exit(0))
 
 p = desktop_Platform()
+# Keep copy of ctrl in platform, too.
+p.ctrl = ctrl
 
 # Copy context to platform.
 def copyContext(c):