RE: [Algorithms] Occlusion culling in outdoor terrains

[Tom F. <to...@mu...>]

The way I did it was to allocate at start of day some fraction of video
memory in large textures just for impostor use. I think the fraction was 10%
of available video memory - something like that. And then the most distant
objects were impostored first, and I'd keep impostoring until (a) I ran out
of video memory or (b) the update heuristics said "you'll need to update
this more than once every 4 frames". 4 frames seemed to be the breakeven
point between using an impostor and just rendering the thing normally.

So your memory use is constant. It also has the nice side-effect that you
don't have to allocate rendertarget textures during the actual game - it can
get tricky, slow, and confuse the texture manager. You just do the
allocations once at start of day.

Tom Forsyth - Muckyfoot bloke and Microsoft MVP.

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> -----Original Message-----
> From: Jason Zisk [mailto:zi...@n-...]
> Sent: 31 July 2003 16:54
> To: gda...@li...
> Subject: Re: [Algorithms] Occlusion culling in outdoor terrains
> 
> 
> > Has anyone done stuff on combining say a forest of trees 
> together into one
> > billboard.
> 
> I've recently got billboards to work in our quite hairy 
> jungle scenes so I
> know can take a guess as to how well something like this would work.
> Basically by fusing multiple billboards into one, you are 
> trading memory for
> CPU.
> 
> By combining objects you are taking a lot of objects each 
> with not so bad
> parallax problems and converting it into one huge object with 
> really bad
> parallax problems.  So you end up having to update that one 
> huge billboard
> much more often than you would the individual trees in it.
> 
> So while you save on ram (which is a major major concern with 
> imposters in a
> scene of 20k+ trees and bushes), you lose out on some of the 
> benefits of
> imposters by having to update it more often.  Also the 
> rendering speed of
> one imposter sprite vs. many isn't that much of an increase 
> to make up for
> having to fully re-render the object more.
> 
> Our scenes have so many trees and bushes ram is a major 
> concern, if I make
> everything an imposter and put the clip at a measely 1000 
> feet it requires
> something like 40 megs of texture ram for everything.  So 
> instead I just
> imposter our bushes, and it only requires about 8 meg but I 
> gain 10fps (not
> so bad).  By combining I might be able to imposter everything 
> into that same
> 8 meg, but who knows if it would be much faster because when 
> you move things
> would be updating more often.
> 
> Hmm maybe something to try when I get some free time to play 
> around with it
> again.  :)
> 
> - Jason Zisk
> - nFusion Interactive LLC