Re: [Algorithms] portal engines in outdoor environments

[Jason Z. <zi...@n-...>]

As usual John has done something I've only idly thought about then
dismissed.  :)  Hope you dont mind me picking your brain on this for the
whole list to see.

What about RAM requirements for this pre-computed list?  If your terrain is
fairly large I can imagine the RAM usage could get quite high.  Do you cut
up the terrain into very large chunks so the visibility lists at each node
don't get too high?

And of course there is the inevitable question of how you compute what is
visible to what node.  I'd assume its done as a pre-process?  And do you do
a full 3D solution with volumes, etc. or a 2.5D type of thing?  I was
thinking some sort of grid-tracing like approach might work, where you check
heights at each grid sample point to see if its visible.

Thanks,

- Jason Zisk
- nFusion Interactive LLC


----- Original Message -----
From: "John Ratcliff" <jra...@ve...>
To: <gda...@li...>
Sent: Friday, August 18, 2000 2:05 PM
Subject: RE: [Algorithms] portal engines in outdoor environments


> In my game the player is almost always on the ground.  I'm just going to
do
> a precomputed visiblity solution on a hash grid against the ground.
> Meaning, wherever you are standing it has precomputed what objects, nodes,
> etc. can be seen from that position.  I've done it before, works fine.
>
> John
>
> -----Original Message-----
> From: Charles Bloom [mailto:cb...@cb...]
> Sent: Friday, August 18, 2000 12:26 PM
> To: gda...@li...
> Subject: [Algorithms] portal engines in outdoor environments
>
>
>
> .. is a hopeless proposition, I think.  I'd just like you
> guys to check my reasoning before I give up.  Consider,
> for example, a building placed on a landscape.  The goal
> is to construct portals so that when you stand on one
> side of the building, you can't see the other.  If the
> player is constrained to stay on the ground, this is
> easy enough, it's really a 2d occlusion problem, and you
> need 8 portals (two * 4 faces of a square in 2d; two portals
> cuz you need one on each side of a face of the square,
> parrallel to that face) which splits the universe into 9
> zones (8 outside and one inside the occluding cube).
>
> However, if we have a plain cube in 3d and the player can
> go anywhere around it, we need 48 portals !! (8 for each of
> the 6 faces on the cube).  Now if you have two cubes near
> eachother, you need massive numbers of portals, and they
> must all not intersect with eachother or other geometry.
> This quickly becomes unworkable.
>
> I think something like a "real-time" occcluder (shadow volumes,
> etc.) is the only hope for outdoors.
>
> --------------------------------------
> Charles Bloom           www.cbloom.com
>
>
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