Brian Furtaw (brian++at++sgi.com)
Thu, 23 Jan 1997 15:25:26 -0500
You have described clipmapping perfectly except. Your application is not
telling the clipmapping routines, man pfClipTexture, what the closest point on
the terrain to the observer is, man pfuGetClosestPoint.
This is my guess as to what you can do to fix this, after you update the
position of the observer, in the updatesim routine, call
pfuGetClosestPoint(...) then call pfClipTexture::setCenter(...) to move the
center of resolution on the clipmap. I guess you may have to do some work to
translate between the closest point and the texture coordinates.
Brian
On Jan 23, 2:27pm, Jim Durbin wrote:
> Subject: Clip map blues...
>
> We, like everybody else these days, are working with large terrain
> databases created from dted and high-res imagry.
>
> We are currently using a 8k by 8k clip-map texture pyramid. When the
> application is running, we notice that the bottom left corner
> (cooresponding to the origin of our world) has a high-res texture tile
> loaded. Moving out from that corner along the x and y axes, the
> texture tiles displayed are from progressively lower-res levels of the
> pyramid.
>
> No matter where we move the viewpt, the resolution of the clip map
> displayed for a given tile does not change. The same behavior is
> observed when the textured object is moved and the viewpt is held
> constant.
>
> Also, in one of our applications, the high-res texture in the bottom
> left corner was replaced when the texture model was scaled up with a
> stale texture that was from another application that was run 4 days
> prior. We were finally succesfull at flushing that texture by
> rebooting the machine. Has anyone else seen this type of behavior?
>
> However, when we load the same model into perfly, the clipmap behavior
> works perfectly.
>
> What am I missing? Is there an extra step that I need to take to
> inform Performer to recalculate the clipmap?
>
> Should I be able to move the textured model and leave the viewpt
> constant (position and hpr with respect to world coordinates) and get
> the same affect as moving the viewpt and holding the textured model
> constant?
>
> We have an Onyx w/ 4 R10000s, one IR pipe with a single RM6/16,
> running Performer 2.1 internal version number 1234000053.
>
> =======================================================================
>
> To make story more interesting:
>
> We know that the clip mapping worked in one of our applications (where
> the view point was changed) last week. The only known change made to
> the machine between success and failure of clip mapping is the
> application of:
>
> Patch SG0001422: IGLOO (IrisGL On OpenGL) patch for O2, Impact
> and InfiniteReality
> Patch SG0001572: 6.2 streams rollup patch
> Patch SG0001601: mediad rollup patch
> Patch SG0001625: dmedia rollup patch
> Patch SG0001650: All platform kernel rollup patch
> Patch SG0001667: XFS rollup #6 for 6.2
> Patch SG0001679: Special rollup for NFS locking FailSafe enhancements
> Patch SG0001692: fix kernel memory consumption on cachefs during find
>
> Removal of those patches has not corrected the situation. It is my
> guess that the patches are irrelevant, but I include here for
> completness.
>
> Any suggestions would be greatly appreciated!
>
> Thanks!
>
> -Jim
>
> --
> _________________________________________________________________________
> | Jim Durbin durbin++at++nrl.navy.mil |
> | ITD Virtual Reality Lab (202) 767-6025 |
> | Naval Research Laboratory (202) 767-1122 (fax) |
> | http://www.ait.nrl.navy.mil/people/durbin |
> | |
> | "It is much easier to criticize an idea than it is to conceive it."
|
> | anonymous |
> | Lack of brains hinders research - The Columbus Dispatch, April 16 |
> _________________________________________________________________________
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>-- End of excerpt from Jim Durbin
-- o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-oBrian Furtaw (brian++at++sgi.com) VisSim Technical Consultant 12200-G Plum Orchard Drive Office:(301)572-3293 Fax: (301)872-3293 Silver Spring, Maryland 20904 OpenGL/ImageVision/OpenInventor/Performer ======================================================================= List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/ Submissions: info-performer++at++sgi.com Admin. requests: info-performer-request++at++sgi.com
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