Optimise my ray tracer - comp.lang.java.programmer

Message from discussion Optimise my ray tracer

Lasse Reichstein Nielsen

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More options 11 Jun 2005, 18:54

Newsgroups: comp.lang.java.programmer

From: Lasse Reichstein Nielsen <l...@hotpop.com>

Date: Sat, 11 Jun 2005 19:54:58 +0200

Local: Sat 11 Jun 2005 18:54

Subject: Re: Optimise my ray tracer

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Jon Harrop <use...@jdh30.plus.com> writes:
> Lasse Reichstein Nielsen wrote:
>> Jon Harrop <use...@jdh30.plus.com> writes:
>>> I have taken startup time into consideration. Java is still consistently
>>> many times slower than most other languages.

>> Is this using the original code that was posted here? Because it can
>> be written significantly better.

> Great, tell me how (provided it doesn't get too much longer).

I posted a link to a slightly optimized version. I don't know if
I am changing the algorithm too much for comparison (e.g., moving
loop invariant code out of the loop) and doing all the I/O at the
end instead of during the computation.

<URL: http://www.infimum.dk/privat/RayTracing.java >
(I changed the class name too, to a more traditional Java format).

I admit to having performed "optimizations" without profiling first,
so there is no telling which change does what, but it does give
me an ~30% increase in speed for size=100.

> With the vector class declared static (what exactly does this do?)

It makes the class more independent of the surrounding class, so each
Vector doesn't have to carry around a reference to a "ray" object that
it never uses.

In a real program, I would put all the nested classes into their own
files.

> it takes 29s, which is not significantly faster.

My guess is that a lot of the time comes from I/O (ok, just O, it only
does output :).

> In contrast, Mlton-compiled SML is much shorter (79 vs 110 LOC) and runs
> about 5x as fast, taking only 6s to ray trace exactly the same image.

Brevity of code is not in itself a quality. Java is often more verbose
than other languages, but I also often find it more readable, because
differet programmers can't invent their own dialect.

> So we really need much better optimisations if Java is going to perform
> anything like as well as the other languages. Am I missing something
> simple, like JIT or optimisation flags?

Can't help you there. I rarely fiddle with flags :)

Btw, is the generated image correct? It looks odd.
/L
--
Lasse Reichstein Nielsen - l...@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleDOM.html>
'Faith without judgement merely degrades the spirit divine.'

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