"Andy Cocker" <big### [at] mariner9fsnetcouk> wrote...
> Sorry... I'm just really enamoured with using radiosity on this particular
> scene.
>
> When I added the spheres, render time went up from around 5 mins, to over
8
> hours! I've no idea why the huge difference... any ideas? The spheres are
> just a simple union of nested #while..#end loops.

The primary reason is most likely that POV can't re-use as many radiosity
sample points.  It will have to take samples at more points because of the
curvature of the surfaces.  The "quality" of a sample point is determined by
how similar that point is to the current spot, looking at the position and
surface normal, among other factors.  If the point is not good enough for
the error_bound value, then more samples are taken, which slows things down.
When the surface normal changes a lot (like on a sphere), more samples have
to be taken.

More samples are also taken inside crevices, where diffuse lighting can
change drastically over a short distance.

This sample-reuse works best on flat surfaces, where the amount of diffuse
illumination doesn't change much from one point to the next.

-Nathan

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