Fogscreen (Community Challenge)

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Whaat
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Fogscreen (Community Challenge)

Post by Whaat » Sun Oct 25, 2009 2:19 pm

Inspired by my trip to Disneyland, I thought a cool Indigo rendering project would be to simulate a fogscreen. This effect is used on a couple of the rides. The fogscreen consists of only an image projector and a device that emits a thin layer of fog to produce the screen. Is it possible to simulate this in Indigo? The thin layer of fog should not be a problem but has anyone ever simulated a movie projector?

The basic challenge is to simulate a projector projecting an image onto a fogscreen in Indigo. The uber-challenge is this:
- Use fluid simulation to produce the fog
- Animate the fog and the projected image
- Animate a character walking through the fog for extra kudos.

Is anyone up to the challenge? :) Post your tests and WIP here! This can also be a very useful learning exercise for the community.

Fogscreen at Disneyland (2:00 mark of video)

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Godzilla
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Re: Fogscreen (Community Challenge)

Post by Godzilla » Sun Oct 25, 2009 2:54 pm

How would you simulate a movie projector, though? (Short of producing a perfect model with tens of millions of polygons)

Perhaps we need a 'laser' emitter? Wherein, the light rays are not distorted as heavily when they are traveling through space, and, like a laser, are projected much more directly than a normal light source?

I've thought about suggesting a laser emitter before, but I don't think there would be much use for it, short of night club & firearm renders.

My two cents, and I'll be sure to try my hand at this challenge. :wink:
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Re: Fogscreen (Community Challenge)

Post by Borgleader » Sun Oct 25, 2009 3:01 pm

wow that is a really cool challenge, y'know what? know that i think of it, i think they use this in stargate. its used to make the aliens screens onboard their spaceships IIRC.

tried finding a video/screenshot on the web but i have been unsuccessful :(
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Re: Fogscreen (Community Challenge)

Post by psor » Mon Oct 26, 2009 1:01 am

What a challenge Whaat. :D ;) I wanna point out that a projector was done already so have a look. ;o))





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Re: Fogscreen (Community Challenge)

Post by CTZn » Mon Oct 26, 2009 4:03 am

Yes that's some challenge Whaat !

The dirtiest way for the screen: a 2d fluid texture blending null with a neutral diffuse_transmitter.

It is surprising that the biggest challenge comes from the video projector...
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Re: Fogscreen (Community Challenge)

Post by OnoSendai » Mon Oct 26, 2009 12:41 pm

Yup, very interesting challenge.
The biggest issue with creating the elements of it are the limitations of Indigo, something which I may have a crack at today.

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Re: Fogscreen (Community Challenge)

Post by psor » Mon Oct 26, 2009 12:53 pm

@Ono

Nick, please have a look at ubiquaque.org. As you can see his implementation of heterogeneous
participating media with single and multiple scattering, I'm wondering if you can bring your hack
back to life. It would be awesome to have something like this in Indigo finally. And if you're open
for a good read then you might read his thesis he wrote concerning "Accelerating the bidirectional
path tracing algorithm using a dedicated intersection processor". It's nothing new but might indeed
could be the key in the future when using GPU's will be more convenient. ;o)





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Re: Fogscreen (Community Challenge)

Post by OnoSendai » Mon Oct 26, 2009 1:32 pm

Yup, I'm talking about non-homogeneous participating media, in particular scattering and absorption coefficients that can vary with position, and are controlled by shaders.

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Re: Fogscreen (Community Challenge)

Post by psor » Mon Oct 26, 2009 1:38 pm

I'm getting more and more curious. Could it be possible to "animate" a shader in the future? ;)



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Re: Fogscreen (Community Challenge)

Post by OnoSendai » Mon Oct 26, 2009 1:50 pm

Well, there's always the possibility to extend shaders to take a time parameter (t).
The main issue with that, however, is that estimation of various quantities becomes harder, such as emitter luminous flux, because it will vary with time.

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Re: Fogscreen (Community Challenge)

Post by psor » Mon Oct 26, 2009 2:00 pm

Maybe I used the wrong term. What I meant was that it could be very useful to change
given values over time. And since animation is exported as one file per frame so with
10 seconds I'd have 250 files when 25fps is used it would be great if exporters or the
material editor could take this into account. That would mean to have the option to
have 250 material/shader files too. As you recognize English isn't my mother tongue
and this makes it a bit hard to explain it in the right way. ;)




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Re: Fogscreen (Community Challenge)

Post by Whaat » Mon Oct 26, 2009 2:06 pm

I don't understand why would you need non-homogeneous media to simulate this effect?

Also, to clarify, I am only asking for a simulation of a projected image, not necessarily a detailed working model of a movie projector.

Can it be done with a few simple elements?
- lightsource
- diffuse transmitter representing the film
- model of lens

What else is needed?

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Re: Fogscreen (Community Challenge)

Post by psor » Mon Oct 26, 2009 2:08 pm

Whaat, that should be it, nothing else needed. I would say Nick is talking about smoke for example. ;o))




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Re: Fogscreen (Community Challenge)

Post by OnoSendai » Mon Oct 26, 2009 2:17 pm

Whaat wrote:I don't understand why would you need non-homogeneous media to simulate this effect?

Also, to clarify, I am only asking for a simulation of a projected image, not necessarily a detailed working model of a movie projector.

Can it be done with a few simple elements?
- lightsource
- diffuse transmitter representing the film
- model of lens

What else is needed?
The problem with using diffuse transmitter for film, is that the diffuse transmitter material alters the direction of light rays. (it scatters them) So it won't work for film.
I was thinking you could model the film with thickness, give it a particular medium, then write a shader for the medium, which sets the absorption colour based on the results of a texture lookup (the texture is the image to be projected). The second option is to create a material similar to the diffuse transmitter material, that absorbs some light, while not scattering the light ray. I prefer the first option, because it's more physically realistic, but the second option may be useful.

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Re: Fogscreen (Community Challenge)

Post by psor » Mon Oct 26, 2009 2:47 pm

That sounds complicated. :lol: :twisted: :wink:

Ok so if I do understand it finally then we can not do it right now.




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