It’s
essentially turning the linear 0 ->
1 output of the sampler info’s
facing ratio into a 0 -> 2 exponential
value.
The
solution I settled on was a fairly
simple one, using masks to define
where the mud would lie on the car,
and then mixing through to a mud shader
in those areas. The mud shader was
mapped separately and could be tiled
and varied without affecting the paintwork.
I
use curves instead of ramps to do
this as I’m used 3D Studio Max’s
way of doing things, but really it
makes no difference how it’s
done.
Integrating
Shaders
Because
all my muddy areas were defined by
masks I could tweak the actual look
of the mud over the whole car without
having to keep going back to Photoshop.
I mapped the two types of mud over
the entire car as a Tri-planar projection,
and then experimented with adding
gradients to have the mud at the bottom
of the car darker (wetter) than at
the top.
Many
of the settings on my shaders were
connected to a control object in the
scene, by changing those settings
I could alter the look of the paint
and mud instantly. These global controls
really sped up the process at the
end, even if they made duplicating
shading networks a pain.
An
early experiment using a different
type of mud. This looked like someone
had chucked a bucket of wet concrete
on the bonnet.
Rendering
As
you’d expect rendering took a
long long time. My frames were averaging
one hour on a 3Ghz machine, and I
ended up rendering an animated sequence
of about 1000 frames !. I was lucky
to get the use of the machines in
work.
Mental
ray had some serious flickering and
crawling issues. Setting the final
gathering min and max radius correctly
really helped prevent this. According
to the mental ray information I found
the max radius should be set to 10%
of the scene width, and the min radius
should be 10% of that. I ended up
with 20max and 2min
I
also played with the BSP settings
to speed up render time, I’ve
no idea why but I had most luck with
BSP size set to 16, BSP depth set
to 60 and BSP max memory set to 0.
Some
renders still had a little flickering
so I had to render out small fix up
patches to place over those areas.
So
there you have it, a little bit of
behind the scenes info on the shading
and rendering of my Mini Cooper.
