Rear Projection Effect
14 messages in this thread
I am trying to create an effect in 3ds4 that simulates a rear projection
screen. I desire a material that will show the shadows cast upon it from back
lighting from the rear, while also showing effects cast from front lights
(colors, projectors).
It is easy to create the front light effects, but so far I am unable to get any
shadows cast from meshes behind it.
So far I have tried all the transparency switches in the ME, but no luck yet.
Any ideas/comments welcomed.
Mike
Hi Mike,
->"I am trying to create an effect…that simulates a rear projection
screen…that will show the shadows cast upon it from back lighting the
rear…I am unable to get any shadows cast from meshes behind it."
I don't think there's any way to create a material that allows shadows cast on
one side of a 2-sided object to show up on the other.
However, maybe a different approach would be to first render just the behind-
the-screen meshes with alpha-split turned on. Then take just the alpha-split
images and use them as an animated opacity map on a flat black polygon that
sits just in front of your projection screen. These animated black cutouts
might simulate the effect you're describing.
I just had a wild thought. Would projecting the alpha channel through a
rectangular-aspect projector light with a *negative* multiplier actually
subtract other light present on the projection screen? Hmmm, it's getting late,
maybe I'm not thinking quite clearly. I'll have to try this out tomorrow.
Cheers,
-Heinz.
Heinz:
Very interesting concepts. This might be a great way to fake the effect. I will
experiment with it.
Thanks for your time.
Mike
Heinz,
PMFJI, but I was wondering about another similar problem, which maybe you have
a suggestion for.
How could you simulate a shadow through say a translucent cloth or umbrella?
For instance, the shadow of structure or a tree on a semitransparent cloth, and
you are on the inside of this cloth and want to see the shadows. I realize
that this is similar, but the problem would be that you would not have a flat
surface or view to use as a map for the "inside" shadows. Do you have any
suggestions?
Thanks,
Doug
Hi Doug:
This is very similar to my problem. If you are just viewing from the inside of
said cloth, you could probably fake the shadows with a projector light.
Placement of the light might be tricky if there are other meshes between the
light and cloth. Excluded lights can still be blocked by the objects that are
excluded from them. Levels of transparency should allow you to see through the
shear cloth, while taking your faked projected shadows.
My problems is seeing shadows projected on both sides of translucent surface.
Heinz was the only one to respond to this problem and I have not had the time
to try his suggestions. I must be very complex, impossible, or in the manual!
Mike
I agree, these are similar problems. I think that the suggestion for
using the alpha channel as a animated texture or projection should
work for your project, but the other seems to be a little more
tricky. I have played with some projections to try and get a decent
"impression" of the effect, but the scene is very complex, and it is
not very easy to duplicate a reverse shadow and apply it to a curving
surface with very good results. Hopefully someone will jump in with
another suggestion.
This sounds like a job for . . . (ta da) camera mapping!
To be honest, I haven't used the effect, but knowing how it works, I
think it will fit the bill for you. Here is the trick. Render the
scene from your lights point of view with the shadow casting object
as a matte object (with a black background). Set up your projector
light as needed. We'll call this rendered series CamMap.IFL.
OK, now you'll need the camera mapping IPAS (for shame, I can't
remember who makes it — just ask around). Anyway, camera map your
object, referencing your projector light as the camera. Now just
create a material as needed with CamMap.IFL (in the texture1 slot)
and apply it to the curved object. Don't forget to flip the curved
object's normals before the final render, so you can see it from the
other side!! VIOLA!! A simulated rear-projection, complete with
shadows!!
For those who are not familiar with camera mapping, it applies
mapping coordinates to an object such that it will seemlessly blend
into a backround image. If the backround image were a rendering from
a spotlight's point of view, camera mapping would cause a material to
be mapped in such a way as to appear "projected" from the spotlight.
The advantage in this case is that the projector light isn't doing
the work, so you can flip the normals of the reciever object and the
texture simply appears on the other side. The disadvantage is that
the mapping coordinates for the reciever object are modified.
Hey, maybe I should write a book!! <VBG>
— James — Choreo Motion —
Great Tip James!
I have not heard of the Camera Ipas. I must go search now. I want it!
Mike
Mike,
If you locate the IPAS, please let me know.
Doug
Doug:
I have not been able to find it anywhere!
Anybody else know where to fine the Camera Mapping IPAS?
Mike
Camera Mapping – available from Digimation & their dealers. I believe list is
$95.
Kevin Krell – Computer Support Associates
Thanks Kevin. Will call them today.
Mike
Thanks for the tip James. I will definately look for the IPAS, and try it out.
Doug
Glad I could help! Good luck on your project.
— James — Choreo Motion —