import java.awt.*;

/** 
 * Uses Shirley's formulation of ray-triangle, w. barycentric coords.
 * This version has a black background and white text.
 * This ray traces a triangle using barycentric coordinates.
 * @author Bob Futrelle
 * @version 0.2, 20 October 2005 (was 3 April 2003)

*/

class TinyRayTrace {

	
	double eihf, gfdi, dheg, akjb, jcal, blkc;
	double a, b, c, d, e, f, g, h, ii, jj, k, l;
	double beta, gamma, t, t0, t1, M;
	int xdim, ydim;
	Color[][] colorArray;
		
	public TinyRayTrace(int xdim, int ydim){
		this.xdim = xdim;
		this.ydim = ydim;
	}
	
	public void doTrace(Tri tri, Color[][] colorArray){
	
		this.colorArray = colorArray;
		for(int i =0; i < 200; i++)
			for(int j=0; j < 200; j++)
				// First point is location, second is displacement
				// Result is orthographic projection
				traceOne(tri,new P3d(i,j,30.0),new P3d(0,0,-60.0),i,j);		
	}

	public void traceOne(Tri tri, P3d raye, P3d rayd,int i, int j) {
		
		setParams(tri,raye, rayd);
		double t = comp_t();
			if(t < 0.0 || t > 1.0)
			return;
		double gamma = comp_gamma();
		if(gamma < 0.0 || gamma > 1.0)
			return;
		double beta = comp_beta();
		if(beta < 0.0 || beta > (1.0 - gamma))  
			return;
		colorArray[i][j] = tri.clr;
	}
	
	// Given a triangle, and ray, we compute all needed coefficients.
	void setParams(Tri tri, P3d raye, P3d rayd) {
	
		a = tri.pa.x - tri.pb.x;
		b = tri.pa.y - tri.pb.y;
		c = tri.pa.z - tri.pb.z;
		d = tri.pa.x - tri.pc.x;
		e = tri.pa.y - tri.pc.y;
		f = tri.pa.z - tri.pc.z;
		g = rayd.x;
		h = rayd.y;
		ii = rayd.z;
		jj = tri.pa.x - raye.x;
		k = tri.pa.y - raye.y;
		l = tri.pa.z - raye.z;
		
		eihf = e*ii - h*f;
		gfdi = g*f - d*ii;
		dheg = d*h - e*g;
		akjb = a*k - jj*b;
		jcal = jj*c - a*l;
		blkc = b*l - k*c;
		M = a*eihf + b*gfdi + c*dheg;
	}
	
	double comp_t() {
	
		return -(f*akjb + e*jcal + d*blkc)/M;
	}
	
	double comp_beta() {
	
		return (jj*eihf + k*gfdi + l*dheg)/M;
	}

	double comp_gamma() {
	
		return (ii*akjb + h*jcal + g*blkc)/M;
	}
	
} // class TinyRayTrace