Create sampler.ml. Defines a super-sampler signature, which implement…

…s super sampling: where color samples are taken at several instances inside the pixel and an average color is calculated. Implements a Stochastic (Random) sampler.

src/sampler.ml

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+open Base
+
+module type S = sig
+  type t
+  val sample : t -> Image.xy -> Color.t
+end
+
+module Stochastic (C: Camera.S) (T: Tracer.S) = struct
+  type t = { camera: C.t; tracer: T.t; n: int}
+  let make ~camera ~tracer ~n = { camera; tracer; n }
+
+  let sample { camera; tracer; n } (x, y) = 
+    let open Color in 
+    let f c = Float.of_int c +. Random.float 1. in
+      (List.range 1 n
+      |> List.map ~f:(fun _ -> C.ray_generate camera (f x, f y) |> T.trace tracer)
+      |> List.fold_left ~init:black ~f:( |+| ))
+      |/ (Float.of_int n)
+end
+
+(* TODO: Add more samplers *)

src/sampler.mli

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+module type S = sig
+  type t
+  val sample : t -> Image.xy -> Color.t
+end
+
+module Stochastic (C: Camera.S) (T: Tracer.S) : sig
+  include S
+  val make : camera:C.t -> tracer:T.t -> n:int -> t
+end
+