> The macro gets called 30000 times, and about 29965 of those times the
> calculated values get returned into the Cp array, but on 35 of those
> calls one of the calculated values doesn't get returned. The value in
> the control point array is whatever the array was preloaded with (in
> this case 0). So about 35 of the 30000 control points of the mesh are
> incorrectly positioned, producing ugly spikes in the surface.
>
> Changes to other parts of the scene (e.g. adding the debugging code that
> I used to determine what was going on) cause the errors to appear at
> different points of the surface.
>
> I've so far failed to reproduce the effect in a minimal scene.

Oh, wow. I've seen this exact same behavior recently in my POVCOMP WIP.
Passing variables by reference (and changing their values within the macro)
fails *very* occasionally for no apparent reason. Changing the code (even
just the number of tokens in code that's never actually executed) changes
the results. I was going to try to find the problem in the POV-Ray source,
but I'm not familiar enough with that part of the code to do it in a
reasonable amount of time. And as you said, it's incredibly difficult to
reproduce the effect on purpose, so I couldn't make a minimal scene to do a
bug report.

 - Slime
 [ http://www.slimeland.com/ ]

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