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jeromeOlivier
08-19-2003, 06:04 PM
Hello,

I'm currently going over Dan Alban's Inside Lightwave 7 chapter 14 & 15, but still haven't made it half way.

I'm currently working on an animation and need to have smoke rise out of the chimney of a train as it speeds along a set of tracks.

The smoke is a single sided polygon attached to a particle emitter using FX-Linker. The polygon has the image of a puff of smoke with an alpha channel to round out the edges.

I am able to get everything working except for one thing: I need to make the polys scale over distance, so that as each puff of smoke drifts away from the emitter, its scale increases UNTIL it reaches 1 (normal scale)

I know I can do this with expressions, but I'm not sure how.

Here's a picture that might help make what I'm trying ot say clearer:

Mylenium
08-19-2003, 11:56 PM
This is not possible with the current versions of LW, since there is no way to acces particle data with expressions. From what I read you possibly would want to use HVs in sprite mode which would yield the same result.

Mylenium

jeromeOlivier
08-20-2003, 01:09 AM
Thank you for replying.

But it's not the particles I'm trying to manipulate, only the polygons that have their motion affected by the emitter.

I know how to do it using sprites, but then I have to render using raytraying to maintain transparency - VERY long renders...

I guess another possibility would be to render the smoke separately and then comp it together in After Effects, but that seems like a waste of time also.

[Emitter.Position.Z]*.1

...or something like that attached to the X and Y of the scale channel of the smoke poly would work, but it is the relative distance between the poly and the emitter that needs to be calculated. Is there a way for me to fetch the information from the range finder plug-in and use that to create the expression?

AArgh!!! This is so frustrating! :(

Mylenium
08-20-2003, 05:15 AM
Hummho, this would mean you had to bake particle motion using FX Linker... Not a very wise thing, 'cos it will be a major part of work and you will end up with lots of unnecessary keyframes for each particle. The expression would then have to be something like(just a suggestion)

[(Particle.Position.Z-Emitter.Position.Z)/(Time-Emission_Time)*scale_multiplier]

Unfortunately all those fancy tools like range finder are pretty useless for expressions 'cos you (once again) cannot access their data. You would have to write the trigonometry yourself.

Mylenium

jeromeOlivier
08-20-2003, 09:17 PM
Mylenium,

Merci beaucoup! I understand now. I finally went the other way and simply used hypervoxel sprites with clip images.

I should definitely learn more about expressions. If you have any recommendations regarding tutorials or reference material, please let me know.

Again, thanks for your help.