> I wonder why Slime's patch for the smooth triangle (and shadow-line
> artifact) problem never made it into MegaPov.  But I'm guessing it's the
> fact that "there is no solution that works in every case".

Well...

The smooth triangle bug *is* a bug and there are solutions which work in
every case. However, this bug is very difficult to fix given the way that
it's ingrained in the POV-Ray code. My bug fix was a hack and did not really
address the underlying issue. I hope (and basically expect) that the code
changes for POV-Ray 4.0 will address this issue and treat the smoothing of
triangles more like normal perturbation so that the bug does not occur.

I believe there are two reasons that my "fix" for this bug was not brought
into MegaPov: first, the best feature of SlimePOV (IMO and probably the
opinions of others as well) was the height field normal bugfix, and that and
other height field bug fixes were put into MegaPov and POV-Ray 3.6; these
were probably a distraction from the triangle normal bugfix. Second, the fix
was very messy and ugly, so there probably wasn't much of a desire for other
coders to put it in their patches.

The shadow line artifact is not a bug, however, and there is no real perfect
solution to it. My solution in SlimePOV is also kind of a hack, and it
doesn't really behave completely intuitively.

I was thinking recently, however, about a different possible solution to the
shadow line artifact: what if there were a keyword that prevented the
*inner* surface of an object from casting shadows? That is, an object with
this flag set would only intersect with shadow rays when the shadow rays hit
it on the outside. The shadow line artifact is caused by self-shadowing, but
that self shadowing is from the *inside* of a nearby part of the object. I
think that this would solve the problem for all objects which are completely
contained (no holes in the surface, either missing triangles in a mesh or
clipped_by). But that tends to be a property of 99% of objects in POV-Ray
anyway.

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

Post a reply to this message