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cytrox

Missile Trail, i3d, glow question

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Hi!

I recently started exploring Houdini and I am currently trying to make myself familiar with the particle system and i3d.

What I am trying to create is a animation of a rocket with a trail of smoke. So far so good, with a simple particle system and i3d (and the help of a lot of helpful postings in this forum :) ) I made the smoke, but now the problem is to give the part near the rocket the look of hot, glowing gas.

What I've done is adding color to the particles, and slightly changing the metacloud shader to export the color as in the volumetrics tutorial and the 3d texture fog shader to use this color instead of the Fog Color attribute.

But this gives me a while colored, yet very faded look. (see attached picture).

So I was wondering if this is even the right approach for such a problem.

I also put a light into the cloud, to give it some luminance (see attached picture in next posting), but still, as I have absolutely no experience in doing such things, I'm not sure if i shouldn't try it another way.

Perhaps just doing the incandescence completely in the compositor? Or working with two particle systems, one for the glowing top part, one for the smoke, and giving the top part a different, non texturefog shader? (But then I had to blend them smoothly somehow)

Or a custom or hacked shader, like adding a custom "glow" attribute to the particles, and using it similar to the color attribute? (Well, I don't know anything about shader writing, but I wanted to learn it anyway.. :) )

Well, I think I'll try some things out, and see what I'm coming up with, but I would be really grateful for any tips or hints! :)

Cheers

Jens

post-21-1060650083.jpg

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Well, I'd suggest that you do your hot fire/gas part of the trail mostly through compositing. It will offer you more control and will be much, much faster. Plus, certain effects, depending on your scene, you'll want to add like camera flashing and glow well beyond the edge of the fire itself you will find very difficult if not impossible to do in one pass in the renderer without coming up with some sort of very cumbersome lens flaring setup that in most cases will not provide you very convincing results.

To isolate the portion just aft of the jet nozzle on the missile I've gone two different ways. The first, and simplest (the way we did it on True Lies), is to render out an eliptical shape that's parented behind your rocket as a seperate pass. You only need the shape for a matte and will most likely want to include your rocket geometry into that element as a matte object. With this matte you'll cut out a chunk of your smoke to erode, blur, and combine in two to three layers (core, soft glow, larger faint halo glow).

Experiment with tinting each layer and using either a SCREEN or ADD operator to mix your layers over the smoke (after it's already layered on your bg). Before mixing each layer control how strong each layer is by either multiplying down their value (individually) with some sort of expression node or a brighness or levels node (different packages offer several ways to achieve the same thing).

Alternately you could do a seperate smoke render that uses a particle system that dies off at the length you want your fire to be and create your various "hot" layers the same as above.

Just a couple suggestions.

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Sorry, I somehow completly missed you response, pockets!

Thanks for your suggestions, that was exactly what I was hoping for, and I will definitly give it a try!

cheers

Jens

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I played a bit with densities and a very bright light (around 200) and got this image, which I guess kinda looks like a hot core with smoke around it. My smoke was almost black, and my density high, so that the light would fall off faster, and only the bits of smoke that stick out would be shaded.

post-21-1062438629.jpg

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