40 replies to this topic

[Jason]

Hi all,

I have been creating an animated effect a fun animation I am starting to do.  The scene is a hot sun beating down so hard that steam is rising off all the surfaces facing the light. So the spec for this is:

Create steam off an object from all it's surfaces facing the sun. All back-faces and shadowed areas should not emit steam.

I have done a simple and efficient version of this and here is a screengrab of it (see attached image). If I get a few techniques suggested, I'll describe how I did it, and perhaps even post up the hip file.

Things that'll get you points:

*) Solve the spec.

*) My setup is real-time - as I drag the light around, the steam will emit from the fresh surfaces and the shadowed area will die out, although it's not a requirement for this challenge, it's nice to have direct feedback.

*) Build it elegantly, with as few work-arounds as you can. But also try to use as few expressions as you can because other people won't understand them if they're complex, and they're slower than using a SOP solution.

*) Try to keep the SOP networks concise and to the point.

*) Try to make it simple for other people to follow, so that if you get hit by a London bus someone else will be able to continue using it without a seance.



Jason.

Attached Images

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[DaJuice]

That is way cool, I have no idea how you did that.
I hope you'll post up the hip after the challenge is done.
Nice idea too, I wonder how many different ways you could do this.
Peace!

[TheUsualAlex]

Bummer. Just when I thought I am close to figuring it out, I was far from it.
Wished I have paid more attention to my high school geometry class back in 9th grade...

Anyway, still thinking. Still thinking...  

[Jason]

well, don't burn out:)

i'll give you 2 clues - diffuse calculation ( dot product ) and ray SOP...

[Stremik]

Does it have anything to do with photons emitted by the lite by any chance?
As usual, I have an idea but don't have enough coding skills to implement it!
I thought, a custom VEXSop coud be written which would take any number of geometry objects as an input(and get their UV coordinates,maybe?)
Then, in this sops parameters woud have to be an option to import a light object.
The Sop woud extract from light, parameters like number of photons emitted by the lite,their IDs and trajectories.
Than, by putting all this together, the sop woud find a coordinate on surface of the model where each photon hits the surface and calculate the angle at which normal faces the surface at this place.
Now the particle could be birthd at this place and depending on the angle
at which the normal positioned relatively to the trajectory of incoming photon, the size of a particle could be controlled.

Me and my ideas!
Does any of it make any sence at all?

[Jason]

Keep in mind that this can easily be performed completely in SOPs, with a reliace on the point SOP and some expressions. In my example, I made a very simple VEX sop because it's clearer to me than a long hscript expression.

You're on the right track, the direction of the light is important. For every point on the surface of the sphere I calculate the light contribution by angle of the point normal to the light source.  More specifically, the dot product of the Normal with the light direction gives you the light contribution on the surface.

In shader speak, dot(N,L)

And then there are the shadows...here I use the Ray SOP.

I'll give you guys more time before I give away the *whole* thing:-D

Ja hay sunn

[DaJuice]

Woa, I just noticed, the box is casting shadows.
Yeah, I'm slow.

[plan9]

doh! that is awesome...and i didnt see the post until now ..silly me      

to the drawing board i go!!!!!  

[Stremik]

Before you give away the whole sceme, say, is there a PointSOP attached to a MergeSOP in Light object?

Jason, I think this Challange idea of yours is GREAT!!!
It's a very effective way of larning and it fits Houdini like any other software out there.
Moreover,I think there should be a whole forum dedicated to it.
We would chalange each other(Not me,not yet anyway)
and it would keep things a lot more interesting.

[Jason]

Thanks - effects is Houdini's strong point and I hope to show people that although the interface lacks some niceties, the core paradigm of Houdini is so incredible.

As for the challenge, I don't necessarily want my exact solution to be discovered : there are many ways to skin a cat. I'd like to hear other peoples' solutions to problems like this. My hints are really just a couple of pushes in certain directions..

I make good use of the Point SOP - it's one of the most versatile and powerful effects-oriented SOPs in Houdini. If you like, you can explain (in plain writing) the methodology you'd take, even though you may not know exactly how to execute it in SOPs. We can talk about your method before you try to implement it.

If we get a lot of interest in the Challenges, then we'll definately set up a dedicated forum for it:) Thanks for your positive response.

Cheers,
Jason.

[stevenong]

I think I have a solution.  

Please take a look at the attached images:





My solution should be close to Jason's. I'll discuss with him off-forum for now & wait till he posts his solution. Else, I'll post mine.  

[Jason]

Hey Steven,

Good going there!  

Yup that looks like you've got it!  Lets wait another day or 2 before we post up our solutions. C'mon plan9, Stremik, DaJuice and everyone else, let's see a quick attempt here

Cheers,
The Tapir of Hangovers.