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Nick Murphy

volumetric fog (FlyFire)

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Only idea - i have not tried it yet.
Implement it as vertex fog
F(x, y, z) - integrated by z axis fog function,
for each lighted vertex V.color = alpha*V.color +
(1-alpha)*F(x,y,z). You should render background fog
also... may be render F(x,y,z) into billboard
grid vertices ?

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hmm, i don't know much about this, though i've looked for stuff on it in the past. i guess there
isn't a whole lot out there on the subject. all i can tell you is that i think, if implemented in
realtime, the stencil buffer is used....

-Nick

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I'll have an article on this topic within a week or
two.

The program will use vertex based multi-pass
blending. (Only one pass for the fog, but it can be
layered on top of other passes). I believe this is
how quake3 does it. It's a good solution for decent
quality, flexibility and speed.

The article will discuss a few other ways of doing it.
particle-based
3d-textures

I hope to expand it to more advanced algorithms,

including animated procedural fog.

I'll post something here when I get it done.

Scott Franke [druid-]
sfranke@usc.edu
druid-'s GLJournal

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i'm beginner in this kind of stuff, so i don't know
some of terms. Can you explain what is stencil buffers?
i heard about them, but didn't find any explanation
thanx

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ok, multipass rendering only good for hardware
rendering, but i was talking about software techniques,
like volumetric fog in Unreal.

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It's a second pass with gouroud shaded polygons.
Doubling the number of polygons, but it could be worse.

You'll notice that having fog in scene will slow down
the Unreal engine quite a bit (check the fps on the
opening shot). I'm not sure what technique they used,
but I'm trying to find out.

Nick:
I'm not familiar with any volumetric fog techniques
that use the stencil buffer. Do you have an example
of one?

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Another idea - for fog with cylindrical symmetry
u can precalculate a set of map (it will be one -
parametrical) and between the map use linear
blending; the corresponding (to From ->To vectors) map
applied to object either as second texture or as
quad + stencil (here is a stencil buffer)template.

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Hmm, looks like a good article (i didn't read it yet
due a lack of time )
But anyway, example works veeery slow on my pc (P166MMX
with S3 ViRGE 3D) - only 1-3 frames per second.

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