Posted-Date: Wed, 10 Mar 93 17:00:38 -0600
Date: Wed, 10 Mar 93 17:00:38 -0600
From: wisdom@geom.umn.edu
Message-Id: <9303102300.AA16707@fuchs.geom.umn.edu>
To: rman@aero.org
Subject: Re: QuickRenderMan on ther NeXT


I vote RiLineStyle goes into the spec 

:-)

Seriously, I see line support as being important in a 3D library. As  
it is now, we have to simulate lines in Photorealistic RenderMan. We  
do this by one of two methods:

1. Using thin cylinders. This slows the rendering process when we  
have lots of lines, and it looks pretty bad when the camera is  
sufficiently close to a cylinder-line (especially at one of the two  
end points).

2. Using polygons. The end points of the line are projected to screen  
space. We compute a screen space polygon that 'fits around' the line  
at a given width. Then we project back into world space to get 3d  
coordinates of the polygon (2 near coincidental vertices at each  
endpoint for thin lines). This works pretty well and yields good  
render speeds, but the line emulation is completely dependent on  
camera placement, so if you're fond of changing the camera  
orientation directly in the RIB file you'll get some pretty odd  
results to say the least - but it looks cool :-)

It would be really nice to see RiLine support in Photorealistic  
RenderMan, and to see RiLineStyle supported in both Quick and  
Photorealistic RenderMan. I can imagine that there would be a bit of  
a performance hit in Quick Renderman, though, for anything other than
just a simple line.

Crossing My Fingers,

SW
wisdom@geom.umn.edu