perhaps not very helpful, but have you tried plugging the incidence into a
mixer_gradient?
experiment with the different types of incidence - there's a 360 degree
incidence based on light - in combination with the gradient you get more
control than from a simple incidence.
also - there is more to it than just the shader - sometimes you need to
mimic/simulate how the real thing works to get a good result in CGI - can be
a combination of modeling, materials, lighting - working with different
layers of objects
some interesting bits of real world info on how reflectors work here:
http://www.madsci.org/posts/archives/2000-12/977675178.Es.r.html
"... All eyes reflect light well because the path for light always works in
both directions. In other words, if incoming light is focused by the cat's
cornea lens and forms a tiny bright spot on the retina... then that tiny
bright spot can send light out through the cornea-lens, and beam it back to
the original source. If you shine light at a cat, ONLY YOU will see the
glowing eyes, since the cat's eyes are beaming the reflected light back
towards the flashlight (and you are seeing some spill-light). People
standing nearby might not see the glow at all. All eyes will "glow" like
this. However certain animals' eyes glow very brightly because their retina
has a reflective layer called the tapetum. (The tapetum improves their night
vision by doubling the amount of light that hits retinal cells, and by
getting rid of diffuse light inside the eye by throwing it back out through
the pupil so bright moonlight won't cause glary washed-out nightime images.)
To REALLY make cats' eyes glow brightly, hold the flashlight near your face
(or clamp it in your mouth) and gaze past it into the distance.
Human eyes do the same as cats, and that's where "red-eye" in flash
photographs comes from. The eyes send the light from the camera flash back
towards the camera. To get rid of red-eye, move the camera flash far from
the camera lens. Tiny cameras create "red-eye" because the photoflash is too
close to the camera lens, and the camera "sees" the light that the eyes are
beaming back to the flash tube.
Very old railroad reflectors used "cats eye" reflectors in the form of glass
lenses with a curved mirror in place of the "retina". If you ever find an
old ball of red glass by the side of the road that has silver on one side,
it's an ancient "cats eye" safety reflector.
Road reflectors on a bike are based on something entirely different. If you
place two mirrors together at a 90deg angle, then all incoming light will
bounce twice and then retrace approximately the same path on its way out.
(Try it, and you'll find that the reflection that you see in the mirror-pair
is NOT REVERSED as it is in a single mirror!) And if you put THREE mirrors
together and look into the corner of them, you'll see an upside- down,
unreversed image of your face. And no matter how you twist the mirrors or
move your head, the image of your face will stay in the same spot. This
device is called a CORNER-CUBE REFLECTOR. It returns incoming light back to
its source.
Bicycle reflectors are composed of hundreds of tiny Corner Cube reflectors
formed into the plastic. (Call this device a "Corner-Cube Array.") When you
look at a bicycle reflector close up, notice that it looks black. The black
color is actually the upside- down image of your eye's dark pupil! If the
reflector facets were lots bigger, you'd see an image of your eye within
each one. Gaze at the reflector while slowly moving the edge of a white
piece of paper across your eye, and just before it blocks your vision,
you'll see small white bits appear in the facets of the bicycle reflector.
If you take apart a bicycle reflector, you'll find that the faceted back of
the plastic is NOT a metal-coated mirror. In fact, if it was metallized, it
would only reflect about 80% of the light; same as normal mirrors. Without
the metal, it reflects 100% of the light. This strange phenomenon occurs
because the light is INSIDE THE PLASTIC when it strikes the tilted facets,
and the 100% reflection is known as "Total Internal Reflection." When light
within a transparent material strikes the inner surface of that material at
a glancing angle, it reflects totally. Total Internal Reflection causes the
surface of water to look silver when viewed from underwater. It causes the
bottom of a glass cup to look silver except where you touch it with wet
fingers. (Try searching the www using keywords "total internal reflection".)
(Try dipping a bicycle reflector into an aquarium or other flat, water-
filled container. Will it still reflect? Or will it become transparent?)
Optical fibers are just reflective tubes. Shine light down the tube, and it
keeps going because it bounces from the walls. But if you've ever looked at
optical fibers, you'll notice that they are NOT METALLIZED like a mirror,
they have no silvery coating. They look like transparent fishing line. I bet
you're way ahead of me now. Yes, that's right, they use "Total Internal
Reflection," just like the Corner Cubes on your bike reflector. That's why
optical fibers can guide light for many miles: it's because the walls of the
fiber don't absorb light at all, instead they reflect 100%."
-----Original Message-----
From: Patrick Neese
Sent: Tuesday, March 24, 2015 5:16 PM
To: softimage@listproc.autodesk.com
Subject: Retro reflective Materials?
I'm looking for something like cat eyes or road signs. Where the
reflection of the light source is affected by angle between the light
to surface to camera. It should also take into account the light
color. If a cat turns it's eyes away the intensity/reflection changes
and/or if the camera shifts off axis from the surface or the light
shifts off axis the intensity/reflection also changes.
So, I've experimented with some Incidence nodes with some crazy
mixing...but it isn't exactly what I would like.
Does anyone know of a way to get a proper retro-reflective material?
Did I miss something in some of the shaders or a shader itself? One of
the BRDF settings?
Thank you for your time.
Patrick