Re: [Yafray-devel] Re: Fresnel effect too dominant for IOR=1.5

[lynx . abraxas]

On 14/01/08 21:59:02, GSR - FR wrote:
> Hi,
> address@hidden (2008-01-14 at 1235.46 +0100):
> > On 13/01/08 20:26:41, GSR - FR wrote:
> > > Hi,
> > > address@hidden (2008-01-13 at 1055.51 +0100):
> > > > IOR. Comparing it with the blender internal raytracer and physical
> > > > values (5 and 1.25,
> > > [...]
> > > > By the way: When disableing RayMirror in the Blender yafray settings
> > > > the fresnel effect does not disappear. It just seems to influence
> > > > the shading ad the sides of the glas.  I'm using yafray 0.9 and
> > > > blender 2.45.
> > >
> > > Blender internal as ref is not a good idea, bugs,
> > > inconsistencies... more artistict than real.
> > >
> > https://projects.blender.org/tracker/index.php?func=detail&aid=7910&group_id=9&atid=125
> > 
> > Thanks GSR for Your reply.
> 
> It was just a private note (quickest demo I could find of "blender no
> good ref"), but this one is public.
> 
> > I know about that bug but I don't think it does concern the fresnel effect.
> 
> The point I was trying to comunicate is that the internal render
> engine is not physically correct in general (bugs + on purpose on some
> parts) so you better focus the issue from other point of view, you
> will stop getting headaches wondering what is going on. ;] There are
> more demos of just doubtful correctness, like arealights vs point
> (smallest arealight should render something that approaches plain
> point light, but it does not, does it?) or artistic optimizations
> (hair shading trick that mixes surface shading with strand one).
> 
> No idea if yafray is physically correct or tries to, nor if params map
> perfectly, but your best bet is looking at its code (comments? docs?)
> and use allowed params until it looks OK to you or looks the same than
> a photo or than "this is physical correct" renderer's result.

After  looking  at  the  code to find  a possible bug I noticed yafray is very
sensitive on the sign of the normals. Checking my blender file I noticed
that  I  had  only turned the normals of the inner part of the bowl outside. 
This gave
the strange appearance of the outside that looked like an over strong  fresnel
effect. Recalulating the normals of the whole gals solved the problem.
It  seems  bender's internal renderer seems not to be dependent of the sign of
the normals and therefor gives a realistic result both times.
Perhaps it should be pointed out in glas/reflection tutorials in what  way  it
matters to yafray where the normals point.

Regards,
Lynx