Re: Culling/Clipping question

New Message Reply Date view Thread view Subject view Author view

Jenny Zhao (zhz++at++dandan.engr.sgi.com)
Fri, 10 Sep 1999 13:45:03 -0700

Please read Chapter4 "Database Traversal" in the IRIS Performer
Programmer's Guide. There is a detailed describtion of
the view frustum culling in Performer.

The culling (determine if a node is inside/maybe inside a frustum)
is done on the host side in the CULL process. Performer
does not rely on the hardware for culling. The clipping in done
in hardware. (Refer to the OPENGL book on clipping)

On Sep 10, 1:08pm, Yohan Baillot wrote:
> Subject: Culling/Clipping question
> Hello Performer community,
>
> How the clipping/culling is done in Performer? Does Performer rely on the
> hardware
> and compute if each point is in 3D is in the viewing frustrum at each frame?
> I was
> wondering if may be the scene graph was used in a way that would faster the
> process
> on the assumption that the view frustrum for the current frame is in a 3D
> attitude
> close to the one of the previous frame.
> I beleive that this is generally the
> case in
> most simulations.

Performer's culling does not use frame to frame cohenrency. Every cull
starts at pfScene node and performs a depth-first, left-to-right
traversal.

> Are the octrees what I am just describing here?
You described a traversal algorithm that takes advantage of
frame to frame cohenrency.
Octree is a hierarchical spacial subdivision of the database.
It provides an efficient data structure for visibility traversal.
Performer does recommand using octrees to organize the databases in
many applications, but it is definitely not a requirement.

>
> Thanks
>
> Yohan
>
> _______________________________________________________________________
>
> Yohan BAILLOT
>
> Virtual Reality Laboratory,
> Advanced Information Technology (Code 5580),
> Naval Research Laboratory,
> 4555 Overlook Avenue SW,
> Washington, DC 20375-5337
>
> Email : baillot++at++ait.nrl.navy.mil
> Work : (202) 404 7801
> Home : (703) 566 3684
> Cell : (407) 222 6359
> Fax : (202) 767 1122
> Web : www.ait.nrl.navy.mil
>
> _______________________________________________________________________
>
>
> -----------------------------------------------------------------------
> List Archives, FAQ, FTP: http://www.sgi.com/software/performer/
> Submissions: info-performer++at++sgi.com
> Admin. requests: info-performer-request++at++sgi.com
>-- End of excerpt from Yohan Baillot

-- 
Jenny Zhao        zhz++at++engr.sgi.com     650 933-5091	IRIS Performer Manager

New Message Reply Date view Thread view Subject view Author view

This archive was generated by hypermail 2.0b2 on Fri Sep 10 1999 - 13:45:25 PDT

This message has been cleansed for anti-spam protection. Replace '++at++' in any mail addresses with the '@' symbol.