Added an attempt not prevent OpenGL from drawing triangle backfaces.

src/graphics.cpp

@@ -444,6 +444,7 @@ void initializeGL(void)
     glEnable(GL_BLEND);
     glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
     glEnable(GL_POINT_SMOOTH);
+    glEnable(GL_CULL_FACE);
 }
 
 void loopGL(void)