class linesegment {
public:
	float x0,y0,x1,y1;
	float currx;
	float incx;
	linesegment* next;
	linesegment* prev;

	linesegment()
		{x0=x1=y0=y1= -1; currx=-1; incx=0; next=prev=0;}
	linesegment(float xfirst, float yfirst, float xlast, float ylast);
	void updatex() {currx += incx;}
};

linesegment::linesegment(float xfirst, float yfirst,float xlast, float ylast) {

	// set endpoints in correct order
	if ((yfirst< ylast) || (yfirst==ylast && xfirst<=xlast)) {
		x0 = xfirst;
		y0 = yfirst;
		x1 = xlast;
		y1 = ylast;
	}
	else {
		x0 = xlast;
		y0 = ylast;
		x1 = xfirst;
		y1 = yfirst;
	}

	// set x-intercept
	currx= x0;

	// set x-increment = inverse slope
	if (y0==y1) 
		incx =  0;
	else 
		incx = (x1-x0)/(y1-y0);
}