x1 = env's x position - (env's width /2) x2 = env's x position + (env's width /2) y1 = env's y position - (env's height /2) y2 = env's y position + (env's height /2) for(y=y1;y>y2 - 1;y++){ draw(x1,y,black); draw(x2,y,black); } for(x=x1;x>x2 - 1;x++){ draw(x,y1,black); draw(x,y2,black); }