// The Great Computer Language Shootout
// http://shootout.alioth.debian.org/
// Fastest version under 100 LOC. Contributed by Jon Harrop, 2005
import java.util.*;
public final class raytracer {
// Use "double delta=Math.sqrt(Math.ulp(1.0))" with Java 1.5 or better
double delta=Math.sqrt(2.22044604925031e-16), infinity=Float.POSITIVE_INFINITY;
class Vec {
public double x, y, z;
public Vec(double x2, double y2, double z2) { x=x2; y=y2; z=z2; }
}
Vec add(Vec a, Vec b) { return new Vec(a.x+b.x, a.y+b.y, a.z+b.z); }
Vec sub(Vec a, Vec b) { return new Vec(a.x-b.x, a.y-b.y, a.z-b.z); }
Vec scale(double s, Vec a) { return new Vec(s*a.x, s*a.y, s*a.z); }
double dot(Vec a, Vec b) { return a.x*b.x + a.y*b.y + a.z*b.z; }
Vec unitise(Vec a) { return scale(1 / Math.sqrt(dot(a, a)), a); }
class Ray {
public Vec orig, dir;
public Ray(Vec o, Vec d) { orig=o; dir=d; }
}
class Hit {
public double lambda;
public Vec normal;
public Hit(double l, Vec n) { lambda=l; normal=n; }
}
abstract class Scene {
abstract public Hit intersect(Hit i, Ray ray);
}
class Sphere extends Scene {
public Vec center;
public double radius;
public Sphere(Vec c, double r) { center=c; radius=r; }
public double ray_sphere(Ray ray) {
Vec v = sub(center, ray.orig);
double b = dot(v, ray.dir),
disc = b*b - dot(v, v) + radius*radius;
if (disc < 0) return infinity;
double d = Math.sqrt(disc), t2 = b+d;
if (t2 < 0) return infinity;
double t1 = b-d;
return (t1 > 0 ? t1 : t2);
}
public Hit intersect(Hit i, Ray ray) {
double l = ray_sphere(ray);
if (l >= i.lambda) return i;
Vec n = add(ray.orig, sub(scale(l, ray.dir), center));
return new Hit(l, unitise(n));
}
}
class Group extends Scene {
public Sphere bound;
public LinkedList objs;
public Group(Sphere b) {
bound = b;
objs = new LinkedList();
}
public Hit intersect(Hit i, Ray ray) {
double l = bound.ray_sphere(ray);
if (l >= i.lambda) return i;
ListIterator it = objs.listIterator(0);
while (it.hasNext()) {
Scene scene = (Scene)it.next();
i = scene.intersect(i, ray);
}
return i;
}
}
double ray_trace(Vec light, Ray ray, Scene scene) {
Hit i = scene.intersect(new Hit(infinity, new Vec(0, 0, 0)), ray);
if (i.lambda == infinity) return 0;
Vec o = add(ray.orig, add(scale(i.lambda, ray.dir),
scale(delta, i.normal)));
double g = dot(i.normal, light);
if (g >= 0) return 0.;
Ray sray = new Ray(o, scale(-1, light));
Hit si = scene.intersect(new Hit(infinity, new Vec(0, 0, 0)), sray);
return (si.lambda == infinity ? -g : 0);
}
Scene create(int level, Vec c, double r) {
Sphere sphere = new Sphere(c, r);
if (level == 1) return sphere;
Group group = new Group(new Sphere(c, 3*r));
group.objs.addLast(sphere);
double rn = 3*r/Math.sqrt(12);
for (int dz=-1; dz<=1; dz+=2)
for (int dx=-1; dx<=1; dx+=2) {
Vec c2 = new Vec(c.x+dx*rn, c.y+rn, c.z+dz*rn);
group.objs.addLast(create(level-1, c2, r/2));
}
return group;
}
void run(int n, int level, int ss) {
Scene scene = create(level, new Vec(0, -1, 0), 1);
System.out.print("P5\n"+n+" "+n+"\n255\n");
for (int y=n-1; y>=0; --y)
for (int x=0; x<n; ++x) {
double g=0;
for (int dx=0; dx<ss; ++dx)
for (int dy=0; dy<ss; ++dy) {
Vec d = new Vec(x+dx*1./ss-n/2., y+dy*1./ss-n/2., n);
Ray ray = new Ray(new Vec(0, 0, -4), unitise(d));
g += ray_trace(unitise(new Vec(-1, -3, 2)),
ray, scene);
}
System.out.print((char)(.5+255*g/(ss*ss)));
}
}
public static void main(String[] args) {
(new raytracer()).run(Integer.parseInt(args[0]), 6, 4);
}
}