Fix blank tiles on large windows and tilt (#522)

vtm-gdx/src/org/oscim/gdx/GdxMap.java

@@ -1,6 +1,7 @@
 /*
  * Copyright 2013 Hannes Janetzek
  * Copyright 2016-2018 devemux86
+ * Copyright 2018 Gustl22
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -149,6 +150,16 @@ public abstract class GdxMap implements ApplicationListener {
             return Gdx.graphics.getHeight();
         }
 
+        @Override
+        public int getScreenWidth() {
+            return Gdx.graphics.getDisplayMode().width;
+        }
+
+        @Override
+        public int getScreenHeight() {
+            return Gdx.graphics.getDisplayMode().height;
+        }
+
         private final Runnable mRedrawCb = new Runnable() {
             @Override
             public void run() {