Not logged in, Join Here! or Log In Below:  
 
News Articles Search    
 

 Home / 3D Theory & Graphics / Beam treezzzz Account Manager
 
Archive Notice: This thread is old and no longer active. It is here for reference purposes. This thread was created on an older version of the flipcode forums, before the site closed in 2005. Please keep that in mind as you view this thread, as many of the topics and opinions may be outdated.
 
Jaap Suter

April 29, 1999, 06:10 AM

What are the drawbacks of beamtrees? Please help me out here cause i don't see any
besides the complexitie of creating realtime bsp trees. I believe however that this can
be greatly optimized.

THanks!

Jaap Suter


 
Harmless

April 29, 1999, 02:59 PM

Jaap Suter wrote:
>>What are the drawbacks of beamtrees? Please help me out here cause i don't see any
>>besides the complexitie of creating realtime bsp trees. I believe however that this can
>>be greatly optimized.

The drawbacks to beamtrees are that they in and of themselves can drive up the cost of the scene to O(n^2) to the number of edges in the scene, just like a BSP tree. With some tweaking you can collapse nodes and reduce the costs considerably however. When I get time to continue my column and get to lighting I'll cover some ways to collapse beamtrees as you build them and reduce the clipping performed by them.

Its advantage is in relation to algorithms like an sbuffer. The beamtree works in object space before you project the polygons into view space, which gives it a small speed advantage, but the real gain comes from the fact that the beamtree works over the entire screen rather than one structure per scanline, and its the only reasonable structure whole-screen based structure that I've found that allows for checking for portal occlusion. Another thing to note, is its not a full fledged BSP tree, all planes pass through the origin, and the construction method is incremental not divide and conquer based.

However, in and of itself, its not a very useful structure. It can be combined with other algorithms to build a decent visibility algorithm, but it doesn't stand well alone.

-Harmless

 
Anis Ahmad

May 01, 1999, 12:02 PM



Jaap Suter wrote:
>>What are the drawbacks of beamtrees? Please help me out here cause i don't see any
>>besides the complexitie of creating realtime bsp trees. I believe however that this can
>>be greatly optimized.

If you like that approach, there are quicker, conservative approaches based on that. Check both Teller's webpage and UNC's webpage they have stuff on using beam-tree like systems to generate occlusion volumes which are basically taking occluders and drawing out occlusion frustums from them.


-- Anis Ahmad

 
Conor Stokes

May 01, 1999, 10:45 PM



Anis Ahmad wrote:
>>
>>
>>Jaap Suter wrote:
>>>>What are the drawbacks of beamtrees? Please help me out here cause i don't see any
>>>>besides the complexitie of creating realtime bsp trees. I believe however that this can
>>>>be greatly optimized.
>>
>>If you like that approach, there are quicker, conservative approaches based on that. Check both Teller's webpage and UNC's webpage they have stuff on using beam-tree like systems to generate occlusion volumes which are basically taking occluders and drawing out occlusion frustums from them.
>>
>>
>>-- Anis Ahmad

The visibility system I am using creates such a single beam per convex shape. And I use a
system where I re-use the allocated memory for the same beam on every check pass.

Conor Stokes

 
This thread contains 4 messages.
 
 
Hosting by Solid Eight Studios, maker of PhotoTangler Collage Maker.