Re: [Algorithms] portal engines in outdoor environments

[Conor S. <cs...@tp...>]

I happen to agree. I'm with John Ratcliff on this though. A precomputed
system. I think I've actually come up with a decent system, that takes LoD
etc into account. This is the problem with precalc'd vis on current systems.

Firstly, the minimum occlusion zone after LoD, is the convex shell of the
bottom of the landscape occluder. Fairly easy.

I use a vertical c-buffer style implementation, with back to front sorting,
similar to Fredo Durand's precalculated occlusion using extend projections
(although, you
could use height intersections of extreme stabbing lines). I then store the
minimum height visible for each node, and make a sort of collapsed balanced
binary tree, which can be sorted by height. Storage is fairly compact (each
node in the tree only contains newly visible objects for that node. The ones
below it are used to find the other information. The tree is split into
nodes between the lowest height of the current visibility node.

For 16*16 sized grid nodes per visibility node, the storage is below 100k in
most instances. (Note, this method is also quickest lower to the ground, and
is slightly
conservative, but accurate enough).

This method should do fairly well in most reasonable cases.

Conor Stokes


>
> .. 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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