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hdace
08-05-2006, 09:22 AM
Hey,

I'm doing a space scene, relativistic FX & stuff. Lots of stars I made myself as single point polys.

I took a photo of a galaxy, made a feathered matte in Photoshop, loaded it in the transparency channel of a 2d poly of with the main photo as the texture. The edges of the galaxy fade into the black of space very nicely.

There's just one problem. The stars behind the "transparent" part of the galaxy are blocked. Other objects, like nebulas and stuff behind the galaxy render through the transparent part no problem, just not the stars.

I've been racking my brain for weeks on this one. What did I do wrong? Do single point polys behave differently with regard to other objects' transparancy? Why?

Thanks for any advice, Hal

Dave Jerrard
08-06-2006, 04:07 AM
Partigons (single point polygons), edges & two point polygons are not visible to ray tracing because they technically have no thickness. Being so anorexic, they'll never be seen by ray trasing, and thus, they're not visible with any of the new cameras, or in reflections or traced transparency. This WILL work though. Sinstead of using transparency on the galaxy, use Additive Transparency. It's on the Advanced tab on the Surface Editor. This most isn't a real transparency - it more like the Screen mode in Photoshop. Black parts of the image, being a value of 0 will nothing to what's behind them, and thus, appear to be transparent, while anything brighter in the surface will appear brighter. I use this technique all the time for the same thing - nebulae, galaxies, explosions, etc.. Particles behind these surface will still be visible because, unless you're tracing the transparency. But again, this will only work in the Classic Camera.

If you must use the other cameras, then I suggest applying HV sprites or Pixie Dust to your stars. A good trick here is to render out a simple lens flare first, without any rings or reflections or streaks. Save that image and then apply it to your HVs or Pixie Dust. Set the size in whichever plugins you're using and you'll have nice little stars that will render fine in all modes (though I'm not sure if Pixie Dust can show up in refraction or reflections).

He Who Thinks There's Something Else Going On With Partigons Now.

hdace
08-06-2006, 09:30 PM
Thanks Dave,

Whenever Dave gives Hal advice, you know you're in trouble.

I tried your excellent ideas, but they didn't work. I think they would work if I was starting from scratch, but this scene is way too complicated for me to re-do the starfield now.

Not sure why ad trans didn't work because it should have. Thank you for teaching me so much too.

And your thought-provoking made me finally realize that actually I can render in stages then composite in After Effects. We'll see how that goes.

Hal