Shading and shaping particle systems 2004-02-19 - By Harvey White
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On Thu, 19 Feb 2004 10:35:06 -0000, you wrote:
>Hi guys,
>
>Long time lurker, rare poster, with a cry for help!
>
>I'm fooling around with the particle systems, trying to make a
>stream of stars. The end result is for a still image, so I'm using
>rectangle particles as billboards and the particle sprite plugin to
>get them all facing the camera. When I drag my star shader onto
>them, they all shade as separate objects very nicely.
>
>Now the tricky bit: I want to give the whole thing a cutaway effect -
> basically take out a pie-section of my ring of stars, or at least
>make them invisible. So far I've tried the following:
>
>1) Boolean subtract a cube from my particle system. The problem with
>this is that it ends up with a vertex object, and my shader ends up
>smeared out across the whole system instead of nicely repeating on
>each individual rectangle.
>
>2) Leave the cube separate. This seems to be catch 22 - if I have
>the cube visible then it blocks out the stars and background (or
>doesn't do anything if I make it transparent), while if I uncheck
>the visibility then it has no effect at all and might as well not be
>there.
Almost works, see below.
>
>3) Using "die on impact" with an invisible/transparent cube, but
>that doesn't seem to have any effect - and I think someone said a
>few days ago that the particle systems aren't aware of anything
>other than the ground...
True, they aren't.
>
>So any ideas? Is there some way I can split my vertex object up into
>5,000 little vertex objects, adjust my shader (I've got Eric's
>plugins), or best of all constrain my particle system to a set
>volume? Or should I just cop out and fake it with Anything Grows?
Well one thing you could do, if you have any sort of program that does
blue screen, is multiple pass rendering. Do the particles against a
blue screen with a blue object in the foreground that is blocking the
particle stream where you want there to be a hole.
Do a background shot of the stars, black background.
Do the composite....
Harvey
>
>Thanks for your time...
>
>Giles
>
>
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