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2 Mar 2024 01:50:11 EST (-0500)
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From: clipka
Subject: Re: GPU usage
Date: 4 Mar 2009 16:10:00
Message: <web.49aeed4adc9638ab26f6761f0@news.povray.org>
Saul Luizaga <sau### [at] netscapenet> wrote:
> I have to desagree, Ihave seen examples on some web pages how the GPU
> beat the crap out of a CPU (FPU included) on certain calculations, I was
> reading about "GPUs as a powerful co-processor" or something like that.
> Those calculations were prety complex for 3D geometry solving and other
> stuff I don't recall well, was like a year or so ago.

Unfortunately, the keywords here are "CERTAIN calculations", and "CO-processor"

Or, to put it another way: There is *some* reason why we're not yet running
computers with GPUs *instead* of CPUs.

GPUs excel in specialized bulk data processing (they can be reprogrammed to
change their specialization nowadays, but that still doesn't invalidate this
statement), while CPUs provide for more flexibility.

I could imagine an approach to write a raytracing engine that could quite easily
"outsource" bulk data to a GPU; however, POV does *not* use this approach, and
can't be made to without a virtually complete rewrite.

I think I'm repeating myself, but anyway: Your proposal seems a nice idea, yet
probably has a too low benefit/effort ratio for the average POV user to place
it anywhere high on the development agenda.


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From: scott
Subject: Re: GPU usage
Date: 5 Mar 2009 06:11:43
Message: <49afb36f$1@news.povray.org>
>  The GPU can only be used to your advantage if you can give it a big
> bunch of calculations to perform, let it crunch the numbers for several
> seconds (or minutes) and then retrieve the results.

The main problem for raytracing is that GPUs don't handle recursion very 
well, GPUs work by running set code on a group of data points, you cannot 
arbitrarily create new data points or even write to several different data 
points in your code.

All GPU code must essentially be structured like this:

For every element I of an array A:
- Read some elements a,b,c,... from other arrays (not array A)
- Do some processing based on a,b,c,...
- Write a single result to element I

As you can see it is totally geared for calculating pixel colours for your 
screen from texture arrays and bump maps etc.

Of course you can chain together blocks like that to do more complicated 
things in clever ways, but a complete raytracer does not fit in to that 
scheme at all really.


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From: Saul Luizaga
Subject: Re: GPU usage
Date: 8 Mar 2009 03:23:22
Message: <49b3726a$1@news.povray.org>
Thank you to all that replied me, I have read all the posts and yes, I 
think my idea has little to no use, and would take some sort of 
translation from POV-Ray parsing and some minimum raytracing to put a 3D 
"preview" in an universal OpenGL format (previous GPU caps diag) to send 
it to the GPU and display it, or some sort of .pov analyzer to create 
such image or something like that. Interesting challenge, I wish I could 
start it.

Thank you all again, you have enlighten me.
Cheers.


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From: Nicolas Alvarez
Subject: Re: GPU usage
Date: 9 Mar 2009 18:58:04
Message: <49b59efb@news.povray.org>
Saul Luizaga wrote:
>  this leads me to ask the experienced programmers here if how huge
> would be to make a rough "previewer", real-time if possibile, for
> POV-Ray? 

http://www.daylongraphics.com/other/povray/patches/

http://www.kfunigraz.ac.at/imawww/thaller/wolfgang/vop-intro.html

and there might be others


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From: oleg
Subject: Re: GPU usage
Date: 14 Dec 2010 02:55:00
Message: <web.4d07226ddc9638ab50f14cc60@news.povray.org>
Hi,
Iam a newbee. A colleague asked me to do some research in using pov-ray and GPU.
After reading your comments it seems not a good idea to render pictures with GPU
power because of single precision. But what about the Nvidia Tesla and its high
DP processing power? Are there any project in progress or does it make sense to
think about using the Nvidia Tesla GPUs for rendering?

greetings
SEb


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From: clipka
Subject: Re: GPU usage
Date: 14 Dec 2010 06:21:18
Message: <4d07532e$1@news.povray.org>
Am 14.12.2010 08:53, schrieb oleg:
> Hi,
> Iam a newbee. A colleague asked me to do some research in using pov-ray and GPU.
> After reading your comments it seems not a good idea to render pictures with GPU
> power because of single precision. But what about the Nvidia Tesla and its high
> DP processing power? Are there any project in progress or does it make sense to
> think about using the Nvidia Tesla GPUs for rendering?

Those comments are outdated, as double precision does not seem a problem 
anymore on modern GPUs (at least the high-end ones, and GP-GPUs such as 
Tesla).

Fusing POV-Ray with GPU would be a challenging task, as POV-Ray's 
internal architecture relies on recursive function calls, which are 
still a problem with GPUs; also, POV-Ray does not provide any 
sophisticated mechanisms to "bundle" rays into batches to undergo 
simultaneous processing (which would be necessary to exploit the full 
power of a GPU); you would need some mechanism to identify "similar" 
rays ("coherence" would be a buzzword here, though not in the laser sense).


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From: nemesis
Subject: Re: GPU usage
Date: 14 Dec 2010 10:50:02
Message: <web.4d079188dc9638abf48316a30@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Fusing POV-Ray with GPU would be a challenging task, as POV-Ray's
> internal architecture relies on recursive function calls, which are
> still a problem with GPUs; also, POV-Ray does not provide any
> sophisticated mechanisms to "bundle" rays into batches to undergo
> simultaneous processing (which would be necessary to exploit the full
> power of a GPU); you would need some mechanism to identify "similar"
> rays ("coherence" would be a buzzword here, though not in the laser sense).

Luxrays is a GPL providing precisely such mechanism:

http://www.luxrender.net/wiki/index.php?title=LuxRays


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From: clipka
Subject: Re: GPU usage
Date: 14 Dec 2010 11:45:38
Message: <4d079f32$1@news.povray.org>
Am 14.12.2010 16:47, schrieb nemesis:

> Luxrays is a GPL providing precisely such mechanism:
>
> http://www.luxrender.net/wiki/index.php?title=LuxRays

Quote from the features list:

triangle mesh primitive support (support for other kind of primitive may 
be added in the future);

That currently makes it an absolute no-go for POV-Ray.


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From: nemesis
Subject: Re: GPU usage
Date: 14 Dec 2010 12:50:01
Message: <web.4d07ae33dc9638abf48316a30@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Am 14.12.2010 16:47, schrieb nemesis:
>
> > Luxrays is a GPL providing precisely such mechanism:
> >
> > http://www.luxrender.net/wiki/index.php?title=LuxRays
>
> Quote from the features list:
>
> triangle mesh primitive support (support for other kind of primitive may
> be added in the future);
>
> That currently makes it an absolute no-go for POV-Ray.

more like a 1-go.


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From: clipka
Subject: Re: GPU usage
Date: 14 Dec 2010 13:38:16
Message: <4d07b998$1@news.povray.org>
Am 14.12.2010 18:49, schrieb nemesis:

>> triangle mesh primitive support (support for other kind of primitive may
>> be added in the future);
>>
>> That currently makes it an absolute no-go for POV-Ray.
>
> more like a 1-go.

no, a 0-go. POV-Ray is too generic when it comes to objects. It doesn't 
really make much sense to make an exception specifically for meshes.


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