Saul Luizaga schrieb:
>> 1) Recursion.  As clipka (Christian?) wrote, it is absolutely 
>> essential for POV.
> 
> I suppose this is unsolvable without an C++ ported OpenCL.

???
Recursion is not a feature of C++, it is also a part of standard C99.

>> 2) Data parallelization versus code parallelization (this is related 
>> to the first, but is not strictly the same).
> 
> they say "an API for coordinating data and task-based parallel 
> computation...", this doesn't help? If it could do both maybe would be 
> of use for POV-Ray.

Did you actually /read/ the spec - or just the enthusiastic introduction?

Sure, it does support task-based parallel computation - why? Probably 
because it also targets classic multi-core CPUs, which are ideally 
suited to task-based parallel computing.

GPUs perform very poorly with task-based parallel computations, due to 
their hardware architecture. A software abstraction layer won't change 
that fundamental limitation.

> I see... maybe if GPGPUs are not use as co-processors but as an 
> auxiliary co-processor that is called on demand, if GPU compliant 
> procedure needs to be processed. Are absolutely sure there isn't a case 
> where a GPU can help? maybe in the middle of a rendering/parsing?

No.

POV-Ray's internal workflow does not support asynchronous computations 
(other than having multiple threads independently render parts of the 
image), so only blocking "calls" to the GPU would be of any use, putting 
the CPU task in waiting state in the meantime. Therefore, only portions 
of the code that can be computed /significantly/ faster by the GPU, or 
have any /significant/ size, would warrant "outsourcing" of 
computations, otherwise parameter passing and task switching overhead 
would bog down performance instead of increasing it.

But the only sections of POV-Ray code that do ask for parallelization 
are RGB color and 3D vector computations, or similarly-sized problems; 
these can be parallelized quite well on modern CPUs as well using SSE2 
(i.e. the GPU will not be much faster), and are heavily intermixed with 
conditional branching (i.e. the size of outsourceable work packages is 
very small)

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