I've written a mini ray tracer for the computer language shootout. The
original version was a 66-line OCaml program which I ported to C++:
http://www.ffconsultancy.com/free/ray_tracer/comparison.html
I have since ported the program to C (icc and gcc), SML (sml-nj and mlton)
and Java (j2se and gcj) and Simon Geard kindly ported it to Fortran 90.
I'd like to see it ported to other languages as well, particularly Haskell
and I'm keen to hear any constructive criticisms of my existing
implementations.
It is interesting to note that the SML is 50% longer than the OCaml. When
compiled with Mlton it is also significantly faster. Here are my timings
(1.2GHz Athlon t-bird) for 128x128 resolution, 4x4 oversampling and 6
levels of spheres:
Mlton 1.316s mlton ray.sml
IFC 1.361s ifort -O3 -u -static-libcxa -o raytracer raytracer.f90
C++ 1.605s g++-3.4 -O3 -funroll-all-loops -ffast-math ray.cpp -o ray
ocamlopt 1.932s ocamlopt -inline 100 ray.ml -o ray
SML-NJ 2.245s sml ray.sml
G95 3.351s g95 -O3 -ffast-math ray.f90 -o ray
C 5.971s gcc-3.4 -lm -std=c99 -O3 -ffast-math ray.c -o ray
Java 6.492s javac ray.java
GCJ 20.316s gcj-3.4 --main=ray -Wall -O3 -ffast-math ray.java -o ray
ocamlc 41.047s ocamlc ray.ml -o ray
Note: the OCaml and C++ implementations timed here are not those on the site
- they are more optimised and longer (keeping within 100 LOC).
The compile times are also interesting:
ocamlc 0.099s
IFC 0.333s
SML-NJ 0.625s
C 0.655s
ocamlopt 0.714s
GCJ 0.723s
G95 0.941s
Java 1.362s
Mlton 8.267s
C++ 8.676s
Here is the SML (for Mlton):
(* The Great Computer Language Shootout
http://shootout.alioth.debian.org/
contributed by Jon Harrop, 2005
Compile: mlton ray.sml *)
fun real n = Real.fromInt n
(* Mlton does not provide a "for loop" construct. *)
fun for (s, e, f) = if s=e then () else (f (real s); for (s+1, e, f))
val delta = 0.00000001 (* FIXME: Where is mach eps in the std libs? *)
val infinity = 1.0 / 0.0 (* FIXME: Where is infinity? *)
val pi = 4.0 * Real.Math.atan 1.0 (* FIXME: Where is pi? *)
(* 3D vector
SML typically uses tuples rather than records (as in the OCaml
implementation). *)
type vec = real * real * real
(* SML allows operator precedences to be declared when defining infix
operators. *)
infix 2 *| fun s *| (x, y, z) = (s*x+0.0, s*y, s*z)
infix 1 +| fun (x1, y1, z1) +| (x2, y2, z2) =
(x1+x2+0.0, y1+y2+0.0, z1+z2+0.0)
infix 1 -| fun (x1, y1, z1) -| (x2, y2, z2) =
(x1-x2+0.0, y1-y2+0.0, z1-z2+0.0)
fun dot (x1, y1, z1) (x2, y2, z2) = x1*x2 + y1*y2 + z1*z2+0.0
fun unitise r = (1.0 / Real.Math.sqrt (dot r r)) *| r
(* Node in the scene tree *)
datatype scene =
Sphere of vec * real
| Group of vec * real * scene list
(* Find the first intersection of the given ray with this sphere *)
fun ray_sphere (orig, dir) center radius =
let
val v = center -| orig
val b = dot v dir
val disc = b * b - dot v v + radius * radius
in
if disc < 0.0 then infinity else
let val disc = Real.Math.sqrt disc in
let val t2 = b + disc in
if t2 < 0.0 then infinity else
(fn t1 => if t1 > 0.0 then t1 else t2) (b - disc)
end end end
(* Accumulate the first intersection of the given ray with this sphere *)
(* This function is used both for primary and shadow rays. *)
fun intersect (orig, dir) scene =
let fun of_scene (scene, (l, n)) =
case scene of
Sphere (center, radius) =>
let val l' = ray_sphere (orig, dir) center radius in
if l' >= l then (l, n) else
(l', unitise (orig +| l' *| dir -| center))
end
| Group (center, radius, scenes) =>
let val l' = ray_sphere (orig, dir) center radius in
if l' >= l then (l, n) else
foldl of_scene (l, n) scenes
end in
of_scene (scene, (infinity, (0.0, 0.0, 0.0)))
end
(* Trace a single ray into the scene *)
fun ray_trace light (orig, dir) scene =
let val (lambda, n) = intersect (orig, dir) scene in
if lambda >= infinity then 0.0 else
let val g = 0.0 - dot n light in
(* If we are on the shadowed side of a sphere then don't
bother casting a shadow ray as we know it will intersect
the same sphere. *)
if g <= 0.0 then 0.0 else
let
val orig = orig +| lambda *| dir +| delta *| n
val dir = (0.0, 0.0, 0.0) -| light
in
let val (l, _) = intersect (orig, dir) scene in
if l >= infinity then g else 0.0
end end end end
(* Recursively build the scene tree *)
fun create level r (x, y, z) =
let val obj = Sphere ((x, y, z), r) in
if level = 1 then obj else
let val r' = 3.0 * r / Real.Math.sqrt 12.0 in
let fun aux x' z' =
create (level-1) (0.5 * r) (x-x', y+r', z+z') in
let val objs = [aux (~r') (~r'), aux r' (~r'),
aux (~r') r', aux r' r', obj] in
Group ((x, y, z), 3.0 * r, objs)
end end end end
(* Build a scene and trace many rays into it, outputting a PGM image *)
val () =
let
val level = 6 (* Number of levels of spheres *)
val ss = 4 (* Oversampling *)
(* Resolution *)
val n = case CommandLine.arguments () of
[s] => (case Int.fromString s of
SOME n => n | _ => 256)
| _ => 256
val scene = create level 1.0 (0.0, ~1.0, 0.0) (* Scene tree *)
in
(fn s => print ("P5\n"^s^" "^s^"\n255\n")) (Int.toString n);
for (0, n, fn y => for (0, n, fn x =>
let val g = ref 0.0 in
for (0, ss, fn dx => for (0, ss, fn dy =>
let val n = real n
val x = x + dx / real ss - n / 2.0
val y = n - 1.0 - y + dy / real ss - n / 2.0 in
let val eye = unitise (~1.0, ~3.0, 2.0)
val ray = ((0.0, 0.0, ~4.0),
unitise (x, y, n)) in
g := !g + ray_trace eye ray scene
end
end));
let val g = 0.5 + 255.0 * !g / real (ss*ss) in
print (String.str(Char.chr(Real.trunc g)))
end
end))
end
--
Dr Jon D Harrop, Flying Frog Consultancy
http://www.ffconsultancy.com
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