From 1380a1a07f211964979128274ecc314465bc3ce1 Mon Sep 17 00:00:00 2001
From: Samrat Man Singh <samratmansingh@gmail.com>
Date: Fri, 11 Mar 2016 11:32:36 +0545
Subject: [PATCH] Add types hitable to support World of multiple objects

---
 src/raytracer.ml | 71 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 63 insertions(+), 8 deletions(-)

diff --git a/src/raytracer.ml b/src/raytracer.ml
index 8990ad01..ca4d2013 100644
--- a/src/raytracer.ml
+++ b/src/raytracer.ml
@@ -6,28 +6,83 @@ open Ray
 type sphere = { center: Vec3.vec3;
                 radius: float }
 
-let hit_sphere sphere ray =
+type hitable = Sphere of sphere
+             | World of hitable list
+
+type hit = { t : float;
+             p: Vec3.vec3;
+             normal: Vec3.vec3;
+             hit: bool }
+
+let hit_sphere sphere ray (tmin, tmax) =
   let oc = sub ray.origin sphere.center in
   let a = dot ray.dir ray.dir in
   let b = (dot oc ray.dir) in
   let c = (dot oc oc) -. (sphere.radius *. sphere.radius) in
   let discriminant = b*.b -. a*.c in
 
+  let no_hit = { t = -1.0;
+                 p = Vec3.of_floats (Float.infinity, Float.infinity, Float.infinity);
+                 normal = Vec3.of_floats (0., 0., 0.);
+                 hit = false } in
+
   if (discriminant > 0.0)
-  then (-.b +. (sqrt discriminant)) /. a
-  else -1.0
+  then
+    let t = (-.b +. (sqrt discriminant)) /. a in
+
+    if (t < tmax && t > tmin)
+    then 
+      let p = Ray.point_at_parameter ray t in
+      { t = t;
+        p = p;
+        normal = unit_vector (sub p sphere.center);
+        hit = true }
+    else
+      let t = (-.b -. (sqrt discriminant)) /. a in
+      if (t < tmax && t > tmin)
+      then 
+        let p = Ray.point_at_parameter ray t in
+        { t = t;
+          p = p;
+          normal = unit_vector (sub p sphere.center);
+          hit = true }
+      else no_hit
+  else no_hit
+
+let rec hit_world world ray (tmin, tmax) =
+  let init_rec = { t = tmax;
+                   p = Vec3.of_floats (-1., -1., -1.);
+                   normal = Vec3.of_floats (-1., -1., -1.);
+                   hit = false; } in
+  List.fold world
+    ~init: init_rec
+    ~f: (fun acc h -> 
+        let hit_rec = (hit h ray (tmin, acc.t)) in
+        if (hit_rec.hit) 
+        then hit_rec
+        else acc)
+and hit h ray (tmin, tmax) =
+  match h with
+    Sphere s -> hit_sphere s ray (tmin, tmax)
+  | World w -> hit_world w ray (tmin, tmax)
+
 
 let get_color ray =
-  let sphere = {center = Vec3.of_floats (0., 0., -1.);
-                radius = 0.5 } in
-  let t = (hit_sphere sphere ray) in
-  if (t > 0.0)
-  then let n = unit_vector (sub (Ray.point_at_parameter ray t) sphere.center) in
+  let sphere1 = Sphere {center = Vec3.of_floats (0., 0., -1.);
+                        radius = 0.5 } in
+  let sphere2 = Sphere {center = Vec3.of_floats (0., -100.5, -1.);
+                        radius = 100.0 } in
+  let world = World [sphere1; sphere2] in
+  let hit_result = (hit world ray (0., Float.infinity)) in
+  let t = hit_result.t in
+  if (hit_result.hit && (t > 0.0))
+  then let n = hit_result.normal in
     mul 0.5 (Vec3.of_floats (n.x +. 1., n.y +. 1., n.z +. 1.))
   else let unit_direction = unit_vector ray.dir in
     let t = 0.5 *. (unit_direction.y +. 1.0) in
     add (mul (1.0 -. t) {x= 1.0; y=1.0; z= 1.0}) (mul t {x= 0.5; y= 0.7; z= 1.0})
 
+
 let write_to_file filename =
   let nx = 200 in
   let ny = 100 in