"Chambers" <ben### [at] pacificwebguycom> wrote:
> From what I understand, POV does a pre-trace to precompute a sample
> tree.  Then, during the actual, render, POV creates any additional
> samples needed.
>
> What if there were a way, during the pretrace, to predict where
> additional samples would be needed?  If so, then all the samples could
> be taken during the pretrace, with no additional sampling during the
> final render, with no loss in quality.

Yes, this would solve the multitasking issues (talking about 100%
reproducibility of shots) during main render.

Unfortunately, I know of only two approaches to collect all the samples needed
before the main render:

(1) Just plain stupidly cover all the surfaces in the whole scene with samples -
which will be a problem for scenes that stretch into infinity.

(2) Perform the full render twice.

The problem is that unless you really *do* the final render, you never know
which regions of the shot may ultimately be reached by some stray ray.

To give a trivial example: If you turn on focal blur, you will find that the
final render will take more radiosity samples - especially in the very first
and very last lines. That's because regions normally just outside the visible
region now need to be mixed in.

Another example are small or strongly-curved reflecting details that pretrace
may not have encountered.

So if we want to really do a complete pretrace, we end up taking the full-detail
shot twice - once with radiosity sampling on, and once without further sampling.
And what's worse: The first pass will be the more expensive one. And it seems we
want to do it in a single task to avoid the trouble already mentioned.

And what on earth are we doing the final render for then?

I don't really think this gets us anywhere :)

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