code: public int getCornerIndex( SquareNode node ) {
  		int index = nodes.indexOf(node);
  
  		int x = index%columns;
  		int y = index/columns;
  
  		if( x <= 0 && y <= 0 ) {
  			return 0;
  		} else if( x > 0 && y <= 0 ) {
  			return 1;
  		} else if( x > 0 && y > 0 ) {
  			return 2;
  		} else if( x <= 0 && y > 0 ) {
  			return 3;
  		} else {
  			throw new RuntimeException("Not corner!");
  		}
  	}
docs: Returns the index of the corner.  0 = (0,0), 1 = (0,w-1), 2 = (h-1,w-1), 3 = (h-1,0)