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Tom Melly wrote:
> "scott" <sco### [at] spam com> wrote in message
> news:416cf59c@news.povray.org...
>
>>> Now, if you could increase your understanding of
>>> http://tag.povray.org/povQandT/miscQandT.html#3dcard , I think I
>>> would be happier :-)
>>
>> I think I would be happier if you could increase your understanding
>> of how pixel shaders work on the latest 3D cards :-)
>>
>
> ... but this misses the point. Irrespective of whether modern 3d card
> acceleration options are compatible with raytracing or not, povray is
> unlikely to support them if it requires custom code.
>
> On the other hand, if the 3d card automatically took over the
> calculation from the main CPU when appropriate....
The way you write code for a pixel/vertex shader is so different from that
of a normal CPU, I think that would be almost impossible.
> That said, given what I understand of POV and 3d cards, unless 3d
> cards were suitable for involvement in *any* intensive CPU activity,
> then I fail to see why they would be of use.
Well, if you write a ray-object intersection algorithm that runs on the GPU,
that would certainly help a lot. Of course POV-ray would need to be
modified (and this will not likely happen, but it could be a patch, or
another raytracer entirely). GPUs are *very* fast at doing the same code in
parallel. So POV could give the GPU a batch of rays to calculate
intersections with, the GPU can go away and do this and return the result
when it's done. During this time the CPU can also be doing the same (and
working out the pixels from the last GPU result). It would certainly speed
things up, look at that link where they guy was getting 30fps from his
simple raytracer and then was getting 1200fps when it was running with the
GPU helping.
Don't forget that GPUs can run pixel shaders at stupid speeds, of the order
of millions of texels/second, that's *far* faster than any code could run on
a normal CPU.
> Povray, after all, is about creating a file from a series of
> calculations - the display of the image is not part of povray's job.
True, and the job of a pixel shader in a GPU is to run code and output a
chunk of data. Normally that chunk of data is then displayed on the screen,
but it doesn't have to be!
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