Displacement can be an excellent tool for creating surface detail, or
to model things that would take far too long using regular methods. But
in 3dsmax (and many other 3d apps), standard displacement has one big
disadvantage: All it can
do is take
a point on a surface and push it outwards from the face normal.
Displacement that doesn't follow the face normal is known as Non-Linear
Displacement (or if the displacement still pushes the point straight
out, but in a direction other than the face normal, this is called
Vector Displacement).
For example, here's a displaced surface like you've
probably seen before...
And here's something similar, except using non-linear displacement to
warp the results in an axis that isn't perpendicular to the face normal.
Specialty Software for achieving
Non Linear Displacement
Non-Linear Displacement has been around for quite some time, and
there's tons of research on it, however, most 3d
applications / renderers don't deal with it very well, if at all. This
is
partly because giving the user control over what direction the
displacement goes is complex from a user interface perspective. Another
reason is
there doesn't seem to be enough interest from the average user to
persuade the software companies to invest much money on the feature. If
it's tough to do and few people would buy it, why bother doing it,
right? So, non linear
displacement has remained the domain of research and a few programmers
willing to roll their own, but there are limited options for the
standard artist.
In mentalray for max, you can use Vector Displacement maps, however,
mentalray provides no method for creating the maps.
If you own the vray Renderer, you can produce Vector Displacement maps
by taking the difference between a low res and highres mesh, baking it
to a vector disp map, then using that map on your low res mesh to
replciate the high res result. Go here
for more info.
And here's an interesting thread on xsibase discussing how to use xsi and mentalray to
do non-linear displacement.
Non Linear Displacement in 3dsmax with Scanline Renderer
This tutorial discusses a technique for doing non-linear displacement
inside max without a special renderer.
Its basic principal is to displace your surface using the
displace modifier (and not the displacement slot in the material) and
then
modify the direction of the resulting mesh using other modifiers. For
this
example, I'll displace a plane with a cellular texture...
But instead of just displacing out, I'll inflate the spheres so that
the displacement rolls back overtop of itself, creating overlapping
surfaces or under cuts...
Here's the max file to create this effect
(max 8 format).
First, make a plane, apply a
meshsmooth modifier with a lot of iterations, since we'll need lots of
tiny
faces to displace.
Next, apply your displace modifier, and place a cellular map in the
displace slot. I adjusted the size of the cellular and few other
parameters to get the following pattern.
Next you want to select the displaced cells. Use a volume select
modifier. You must use volume select instead of say a poly select,
because you want to select an area, not specific vertexes/faces. That
way, if
you need smother displacement, you can increase the number of
meshsmooth iterations and your volume select modifier will still select
the same stuff. For the volume select, I select the part of the plane
that's not displaced, set it to vertex, then click invert so that I'm
now selecting the
vertex that make up the cells, then I apply a soft selection, and
adjust the soft selection
curve to my liking (experiment with this curve to get a variety of cool
effects). The red and orange means those vertex are selected, the
yellow and
green are partly selected, and the blue are not selected at all.
Now apply a push modifier. Push will take a face and push it along its
face normal. It will react with the soft selection by inflating the
cells so instead of just bumps going straight up, you now have inflated
nodules, like balloons coming out of your surface.
As a final touch, I put a polyselect modifier (to take myself out of
subobject mode) followed by a relax modifier set to a few iterations on
top
in order to smooth out some of the displacement artifacts.
Here's another example file, squiggle.max
(max 8 format), a squiggly spike. This uses the same
principals, except I'm using an xform modifier instead of a push to
modify the direction of my displacement.
Hopefully this will give you some of your own ideas on how to achieve
non-linear displacements.
