Am 18.05.2018 um 19:00 schrieb William F Pokorny:

> Chrisoph added this bit of code in blob.cpp to avoid visible seams:
> 
>   DBL depthTolerance = (ray.IsSubsurfaceRay()? 0 : DEPTH_TOLERANCE);
> 
> I've been running with DEPTH_TOLERANCE at 1e-4 for a long time in my
> personal version of POV-Ray which fixes all the blob accuracy issues
> except for the subsurface one.

For subsurface rays it's safer to keep it at exactly 0.

The `depthTolerance` mechanism, to all of my knowledge, is in there to
make sure that transmitted, reflected or shadow rays don't pick up the
original surface again.

This problem is absent in rays earmarked as subsurface rays (presuming
we have high enough precision) because such rays are never shot directly
from the original intersection point, but a point translated slightly
into the object. So subsurface rays already carry an implicit
depthTolerance with them.

> It could be adjusted so as to push more solve_quartic rays into sturm /
> polysolve, but it's aleady the case most difficult-coefficient rays are
> unnecessarily run in sturm / polysolve when solve_quartic would work
> just fine. The right thing to do is let users decide when to use 'sturm'
> and this set of commit dumps the difficult_coeffs() code.

Would it make sense to, rather than ditching the test entirely, instead
have it trigger a warning after the render (akin to the isosurfaces
max_gradient info messages) informing the user that /if/ they are seeing
artifacts with the object they may want to turn on sturm (provided of
course sturm is off)?

Post a reply to this message