Angus Dorbie (dorbie++at++multipass.asd.sgi.com)
Fri, 30 May 1997 15:23:56 -0700
The only flaw I can see is that you only need one channel to combine
the three textures onto the mesh for the second pass.
Unfortunately the entire scheme as originally conceived is flawed. The
pixel fill and texture readback from the framebuffer is 50% redundant
so a 3 channel solution is far from optimal. It also has some nasty
perspective pixel/angle variance agross the primary channels which need
to be > 120 degrees FOV.
For better efficiency look at my environment reflection mapping code.
It's in the reality centre directory on sgigate.sgi.com in pub performer.
I think it's called env_map.tar.Z or similar.
This code procedurally generates a mesh for an entire sphere and the
pixel fill & image readback can be made 100% efficient and it has better
pixel/angle distribution.
You need to modify this code to draw 5 channels in a hemicube config
instead of 6 channels in a cube, you can also ignore the third pass
for the environment mapping since you have different objectives.
If you are any good these modifications should be easy.
You should rearrange the channels since the cube is laid out to look
good rather than provide efficient download but the theory is sound
and should provide efficient fill and readback.
Cheers,Angus.
On May 30, 9:59am, Shawn Soeder wrote:
> Subject: distortion correction
> Performers,
>
> I'd like to do distortion correction for three channels projected onto a
> spherical dome using an single- (soon to be multi-) pipe IR machine. Can
> anyone direct me to any info on the subject?
>
> If there are no references, is the following roughly in the right direction?
>
> 1) Make two pfScenes, one with the geometry I want to render and one with the
> geometry for the correction.
> 2) Render the first pfScene into three channels that cover the required
area.
> 3) After the pfDraw, copy the framebuffer to texture memory using
> pfSubloadTex.
> 4) Reconfigure the channels to their proper size/orientation for the second
> pass.
> 5) Render the second pfScene into the three channels, projecting the
> downloaded texture onto the new geometry.
> 6) Send the output to the projectors in the dome.
> 7) Look at the results, smile and experience quiet satisfaction.
>
> Thanks
> Shawn
>
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>-- End of excerpt from Shawn Soeder
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