One thing I can't figure out...

How do you do a ghost or predator effect on a graphics card, like with 
opengl or directx or something like that?  I.e., as a vertex/pixel shader.

I understand how you do shadows, and reflections, and how to do something 
like a lens bloom where you post-process the whole image.  What I am not 
sure I've figured out is how to post-process only part of the screen you can 
see. I.e., if the "predator" walks behind a tree, you want the parts you can 
see to distort what's behind it, but you don't want to distort the tree he's 
behind.

The only thing I can think of is that you save the depth map along with the 
image, and then you only post-process the things at the same depth as the 
model of the predator, or something like that.  But how do you know what 
that is? Re-render just the predator in a separate buffer?

Alternately, you *could* render everything twice, with the predator having a 
pixel shader that just made it white, everything else being black. But then 
you're rendering the whole scene three times.

Is there a better way to do that?

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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