Mini ray tracer - comp.graphics.rendering.raytracing

Message from discussion Mini ray tracer

tbp

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More options 9 May 2005, 23:51

Newsgroups: comp.graphics.rendering.raytracing

From: "tbp" <tbp...@gmail.com>

Date: 9 May 2005 15:51:11 -0700

Local: Mon 9 May 2005 23:51

Subject: Re: Mini ray tracer

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Matt Pharr wrote:
> > [demonstration that "inline" vector math makes C++ programs faster
> > elided]

You've missed the point.
a) he's telling the OCaml compiler to inline everything it can while
not giving its c++ counterpart opportunities to do so; fairness?
b) more importantly he's passing large structures by _value_ and i've
turned them into _references_.

In fact if you do the same for other hotpath functions as in:
19c21
< virtual void intersect(double &, Vec &, Ray) = 0;
---

> virtual void intersect(double &, Vec &, const Ray &) = 0;

26c28
< double ray_sphere(Ray ray) { // Intersection of a ray with a sphere
---

> double ray_sphere(const Ray &ray) { // Intersection of a ray with a

sphere
35c37
< void intersect(double &lambda, Vec &normal, Ray ray) {
---

> void intersect(double &lambda, Vec &normal, const Ray &ray) {

50c52
< void intersect(double &lambda, Vec &normal, Ray ray) {
---

> void intersect(double &lambda, Vec &normal, const Ray &ray) {

then the c++ version becomes 50% faster than originally (and in fact,
unconditionally faster than the OCaml version), without adding a single
line.

You'll notice i haven't even fixed the gratitious use of virtual
functions, and other details that force standard compliant c++
compilers to pessimize a lot when facing such... hmm.. source.

I'm sure OCaml is a wonderful & expressive language, but crafting such
a fishy c++ equivalent to make it shine (because you have an agenda) is
a despicable practice.

> > If your point was to show how to write unbelievably inneficient
code in
> > C++, you've succeeded.

> I think the point was to have some fun and to make a little demo that
shows
> how a functional language like OCaml can give rise to nice short
expressive
> programs while still delivering competitive performance. And for
those
> goals, the OP succeeded!

> Note also that he mentions on his web page that he's doing this for
"the
> computer language shootout benchmarks",

http://shootout.alioth.debian.org/.

> That page clearly points out all the caveats around benchmarks like
these
> (to the point that they can be effectively meaningless in the real

world.)
I have nothing against such benchmarks when they are not clearly
rigged.

But i guess the main point of the whole operation wasn't fair
benchmarking, education, or fun but selling books: "This program has
demonstrated some of the ways that OCaml improves upon C++. For a
thorough introduction to OCaml, read our book "Objective CAML for
Scientists".

Or put another way, that's a sad PR stunt.

Have a nice day.

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