void midpoint(int x0,int y0, int x1,int y1)

{
int dx, dy, incrE, incrNE, d, x, y;
	dx = x1-x0;
	dy = y1-y0;
	d = 2* dy - dx;
	incrE = 2*dy;
	incrNE = 2* (dy-dx);
	x = x0;
	y = y0;
	for(x=x0; x<x1; x++) 
	{
		if(d <=0) 
		{
			d = d + incrE;
		} else 
		{
			d = d + incrNE;
			y = y + 1;
		}
		drawDot(x,480-y);
	}
}