// Element of Ray Diagram
// David Eppstein, UC Irvine, 18 May 1997

import java.lang.*;

public class RayDiagObj extends DistancedObject {
	public double x, y, dx, dy, t;
	public RayDiagObj(double ix, double iy, double idx, double idy) {
		x = ix; y = iy; dx = idx; dy = idy;
		t = Double.POSITIVE_INFINITY;
	}
	
	// For what value of t is this(t) on line of ray r?
	// Returns infinity if no crossing exists
	public double crosstime(RayDiagObj r) {
		double det = dx*r.dy - r.dx*dy;
		if (det == 0) return Double.POSITIVE_INFINITY;
		double ct = (r.dy*(r.x-x) - r.dx*(r.y-y))/det;
		if (ct < 0.0 || ct >= t) return Double.POSITIVE_INFINITY;
		return ct;
	}

	// Distance function is latest of two crossing times
	public double distanceTo(DistancedObject d) {
		if (!(d instanceof RayDiagObj)) return Double.POSITIVE_INFINITY;
		RayDiagObj r = (RayDiagObj) d;
		double dr = crosstime(r);
		double rd = r.crosstime(this);
		if (dr < rd) return rd; else return dr;
	}
}