--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/demos/ray.d	Mon Nov 12 06:32:46 2007 +0100
@@ -0,0 +1,96 @@
+//import std.stdio, std.math, std.string;
+//import tools.base;
+
+double delta;
+static this() { delta=sqrt(real.epsilon); }
+
+struct Vec {
+  double x, y, z;
+  Vec opAdd(ref Vec other) { return Vec(x+other.x, y+other.y, z+other.z); }
+  Vec opSub(ref Vec other) { return Vec(x-other.x, y-other.y, z-other.z); }
+  Vec opMul(double a) { return Vec(x*a, y*a, z*a); }
+  double dot(ref Vec other) { return x*other.x+y*other.y+z*other.z; }
+  Vec unitise() { return opMul(1.0/sqrt(dot(*this))); }
+}
+
+struct Pair(T, U) { T first; U second; }
+typedef Pair!(double, Vec) Hit;
+
+struct Ray { Vec orig, dir; }
+
+class Scene {
+  abstract void intersect(ref Hit, ref Ray);
+}
+
+class Sphere : Scene {
+  Vec center;
+  double radius;
+  this(ref Vec c, double r)
+  {
+    center = c;
+    radius = r;
+  }
+  double ray_sphere(ref Ray ray) {
+    auto v = center - ray.orig, b = v.dot(ray.dir), disc=b*b - v.dot(v) + radius*radius;
+    if (disc < 0) return double.infinity;
+    auto d = sqrt(disc), t2 = b + d;
+    if (t2 < 0) return double.infinity;
+    auto t1 = b - d;
+    return (t1 > 0 ? t1 : t2);
+  }
+  void intersect(ref Hit hit, ref Ray ray) {
+    auto lambda = ray_sphere(ray);
+    if (lambda < hit.first)
+      hit = Hit(lambda, (ray.orig + lambda*ray.dir - center).unitise);
+  }
+}
+
+class Group : Scene {
+  Sphere bound;
+  Scene[] children;
+  mixin This!("bound, children");
+  void intersect(ref Hit hit, ref Ray ray) {
+    auto l = bound.ray_sphere(ray);
+    if (l < hit.first) foreach (child; children) child.intersect(hit, ray);
+  }
+}
+
+double ray_trace(ref Vec light, ref Ray ray, Scene s) {
+  auto hit=Hit(double.infinity, Vec(0, 0, 0));
+  s.intersect(hit, ray);
+  if (hit.first == double.infinity) return 0.0;
+  auto g = hit.second.dot(light);
+  if (g >= 0) return 0.0;
+  auto p = ray.orig + ray.dir*hit.first + hit.second*delta;
+  auto hit2=Hit(double.infinity, Vec(0, 0, 0));
+  s.intersect(hit2, Ray(p, light*-1.0));
+  return (hit2.first < double.infinity ? 0 : -g);
+}
+
+Scene create(int level, ref Vec c, double r) {
+  auto s = new Sphere(c, r);
+  if (level == 1) return s;
+  Scene[] children=[s];
+  double rn = 3*r/sqrt(12.0);
+  for (int dz=-1; dz<=1; dz+=2)
+    for (int dx=-1; dx<=1; dx+=2)
+      children~=create(level-1, c + Vec(dx, 1, dz)*rn, r/2);
+  return new Group(new Sphere(c, 3*r), children);
+}
+
+void main(string[] args) {
+  int level = (args.length==3 ? args[1].atoi() : 9),
+    n = (args.length==3 ? args[2].atoi() : 512), ss = 4;
+  auto light = Vec(-1, -3, 2).unitise();
+  auto s=create(level, Vec(0, -1, 0), 1);
+  writefln("P5\n", n, " ", n, "\n255");
+  for (int y=n-1; y>=0; --y)
+    for (int x=0; x<n; ++x) {
+      double g=0;
+      for (int d=0; d<ss*ss; ++d) {
+        auto dir=Vec(x+(d%ss)*1.0/ss-n/2.0, y+(d/ss)*1.0/ss-n/2.0, n).unitise();
+    g += ray_trace(light, Ray(Vec(0, 0, -4), dir), s);
+      }
+      printf("%c", cast(ubyte)(0.5 + 255.0 * g / (ss*ss)));
+    }
+}