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CD
SHADER TUTORIAL
Or "How to fake a diffraction map",
by Leo Santos
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Before
anything, let me say that although this tutorial is specific for
3DS Max, the concepts can be applied to any software, so if you
use other programs feel free to go ahead.
You
can notice I used the word "diffraction". That is the
physical phenomena we'll be simulating in this tutorial, in a very
simple way, using only Max's native gradient ramp shaders (or Maya's,
or XSI's, or Lightwave's ...). You can learn more about diffraction
here. Let's
start, shall we?
First
thing, we create a simple geometry, basically some extruded splines.
One is a flat surface, the metallic foil inside the CD, the others
are the plastic parts that cover it.
Now
we create two materials, one for the plastic, a basic transparent
shiny material, and one for the actual CD surface, the metallic
foil where the information is recorded. We'll focus on this one
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Let's
use the Anisotropic Shader, because it provides better hilights
than the old Blinn shader in Max (which tends to over-saturate
around the hilights).
Keep
the diffuse color dark for now, but you'll be able to fine
tune it later.
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Now
we'll do a generic environment reflection. A gradient ramp
map will do it. You can use any map you want, but I like gradient
ramps because you get a lot of control over the final result.
Set
it to spherical environment, and it will behave as a sphere
that wraps around the whole scene, perfect for a reflection.
Keep
in mind that this is a basic setup, you can have all sorts
of variations, including raytraced reflections, but it may
be more difficult to make it look like you want.
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Well,
let's see how it looks so far. Press F10 and render it.
Naah,
not exactly what we need.... let's keep working on it.
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Next
we'll simulate the "rainbow" effect caused by the
light diffraction. It's very simple, actually. Just drop another
gradient ramp, this time on the Specular color slot, and add
the colors.
Like
the reflection, this one will be a Spherical environment.
Notice
the gradient type is set to "normal". This
handy feature makes the gradient color depend on the angle
between the polygon normal and the camera.
There
may be other ways to do it, and even ready to use rainbow
shaders, but what's great about this way is that, again, you
can tweak the look as much as you want.
One
thing to keep in mind, tough, is that different programs (or
base shaders, like the Brazil R/S advanced shader) may not
behave like Max's Anisotropic shader, and you may have to
actually map the rainbow gradient directly on the reflection.
But if you render this shader in Max, regardless of the render
you should get the same result (I tested it on the Scanline
renderer, Brazil R/S and Mental Ray).
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Ok
let's see it now.
Better...
but not "good" yet.
Now comes the little trick... we'll add a bump map, so it fakes
the surface curvature, in order to see a wider range of the reflection
map. How do we do it?
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We
add another gradient ramp!
This
time, on the bump map channel. Why? Remember that we set
the rainbow gradient to "normal". Well, bump maps
(or normal maps) affect the normal of a surface.
If
we use a smooth radial gradient from white to black, and
map it properly, we'll fake the surface into being curved,
thus seeing much more of the reflection map.
You'll
have to apply a planar mapping on the metal foil object.
I used map channel 01.
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This is how the Bump map must look applied on the surface.
Ok,
Now we render it.
Tah
Dah!!!
Some final considerations:
Different CDs under different light conditions and in different
environments will have a different look. Play around with the parameters
and maps until it looks like you want.
It will render just fine in Scanline, but using renderers like Mental
Ray or Brazil (or Vray, etc...) will give you a better sampling,
specially on the borders, where the bump map tends to look crunchy
without a good sampling.
All
images and text are copyrighted, don't use without permission !
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