View Full Version : dispersing hypervoxel smoke

07-26-2004, 07:02 AM
Hi all--

I'm doing a scene where I'm compositing in a smoke trail from the firing of a bazooka.

Hypervoxels is working great for the initial effect, but I'm having trouble when it comes to the smoke dispersing. I've attached an image of what I've got so far... a nice chunky path of smoke as the projectile launches towards the target... but then I need that smoke to fan out and slowly disappear in a realistic way.

I've managed to get the particles to move away from the path, increase in size and become 0 opacity relative to partical age, but it just looks like a bunch of chunks of smoke-- not the even dispersion I'm looking for.

Any suggestions? I've read the smoke tutorial on newtek, but can't seem to isolate the parameter that'll get my smoke to disperse naturally.

Thanks a ton!

07-26-2004, 08:48 PM
Do you have the hypervoxels set to sprite? From the tutorials I have seen the smooke looks more natural using sprite than the other two settings.

Triple G
07-27-2004, 12:49 AM
Lately I've been doing a lot of shots with a similar effect to what you're going for. There are a lot of parameters that can help you control the look of your smoke fading out. First off, if you have the time to render it, I'd recommend using volume mode instead of sprite mode, and turn on volumetric antialiasing with motion blur...it can be a bit of a render hit, but I've found that sprite mode while relatively fast to render, has a tendency to flatten out and look somewhat cheap. The motion blur will help immensely in making it look less like individual chunks and more like a smooth flow. I've also found that using smaller voxels with an increased number of particles can help as well. You can sort of "cheat" motion blur by applying a stretch value to your HV's based on particle velocity, but things can get a little funky with this, especially if you have align to path turned on...I invariably get a few stubborn particles who randomly decide to flip out and point in odd directions. Not to mention the fact that turning on stretching will increase your render times, so use it sparingly.

As for the settings of the HVs themselves, you sound like you're headed in the right direction with gradients based on particle age for the opacity, density, size, etc. You could also try a gradient based on particle density, so that the more the particles move away from each other, the more transparent they become. Have a look to make sure you have a little bit of explosion on your particles as well, as this will cause them to disperse from where they were emitted. You may also want to try adding a slight turbulent wind in the trail of the smoke to randomize things a little.

Good luck...hope this helped a bit. :)

*edit* If you're able to render the particles in a separate pass, I'd highly recommend doing so. This way you can render them at half-res and then scale them up, which will not only save you render time, but will help soften their look a little as well.

07-27-2004, 08:54 AM
Thank you both so much for your replies. I currently have my hypervoxels set to volume mode.

I'll try some of the suggestions made and report back if I make any improvements.

Thanks again!

07-27-2004, 10:38 AM
I think matching the video lightning needs some work

07-27-2004, 10:42 AM
haven't started on lighting yet. just trying to get the hypervoxels working first.

07-27-2004, 12:47 PM
Originally posted by batboy74
haven't started on lighting yet. just trying to get the hypervoxels working first.

ok, im a "hurry-guy" :D