POV-Ray : Newsgroups : povray.pov4.discussion.general : A serious question about massively parallel architectures (ie GPUs) : Re: A serious question about massively parallel architectures (ie GPUs) Server Time
2 Dec 2023 13:09:43 EST (-0500)
  Re: A serious question about massively parallel architectures (ie GPUs)  
From: Edouard
Date: 20 Jan 2010 03:55:00
Message: <web.4b56c3ca7e508fbb4692fdd50@news.povray.org>
Chambers <Ben### [at] gmailcom> wrote:
> Currently I'm waiting for a scene to render.  And you know what's
> killing render time?
>
> Spawning.
>
> With focal blur creating dozens (I had to turn it down from hundreds) of
> rays per pixel, textures which are averages of 8 (I turned it down from
> 16) glass textures which each have reflection *and* refraction, area
> lights, media, etc... almost every decent effect in POV is achieved via
> taking large numbers of samples or spawning large numbers of rays.
>
> So, I started thinking about how to speed things up.  Obviously, the
> single easiest way to do so is to reduce the number of rays that need to
> be shot.  Well, I've already turned down the settings, and simplified my
> textures...  there's not much else I can do in that category.

I've taken quite a different approach for this problem - there's probably a
large number of names for it, but I'm calling it "stochastic rendering":

I render the scene multiple times (often 200, 400 or more times), but each pass
has a very simplified, but at the same time completely randomised, set of
paramters. When all those renders are summed together into one image, the random
elements all combine to give a final scene that looks like one with a much more
complex set of parameters.

Critically, when there are multiple "features" that all usually interact to push
render times sky-high, I try to construct a scene that has the interaction as
low as possible, and can render a few hundred images very quickly (each pass
taking anything from 10 seconds to maybe a minute or two).

On multi-core machines I simply fire off as many POV processes as I have CPUs
(or is that ALUs?).

I really must post a set of examples of each kind of effect that created with
the technique, and then some examples of combining them all together.

A really really old example of multiple area lights, blurred floor reflection,
anti-aliasing, focal blur and blurred refraction all done with stochastic
rendering:

One pass: http://www.flickr.com/photos/26722540@N05/3094525065/
400 passes: http://www.flickr.com/photos/26722540@N05/3094524731/

Cheers,
Edouard.


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