Re: pfBox and pfSphere

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Sharon Clay (src++at++rose.asd.sgi.com)
Mon, 8 Jul 1996 11:18:37 -0700

+>---- On Jul 8, 11:30am, Steve Baker wrote:
> Subject: pfBox and pfSphere
->From guest++at++holodeck.csd.sgi.com Mon Jul 8 10:04:41 1996
->Date: Mon, 8 Jul 96 11:30:24 -0500
->From: steve++at++mred.bgm.link.com (Steve Baker)
->To: info-performer++at++sgi.com
->Subject: pfBox and pfSphere
->
->Is there an 'official' way to distinguish an empty pfBox or pfSphere?
->
->The man pages don't indicate the existance of a pfIsEmptyBox or
->pfIsEmptySPhere - but they hint that there is a 'special' representation
->for empty boxes and spheres.
->
->By experiment I see that empty Spheres have a center at (0,0,0) and a radius
->of -1.0, and pfBox'es have really large numbers for 'min' and really large
->negative numbers for 'max'.

That is the state of new spheres and spheres and
that created by pfMakeEmpty*()

Empty spheres and cylinders have any radius < 0.0.
Empty bboxes have min[0] > max[0] (this satisfies a fast empty check)

->
->What's not clear is exactly which of these criteria are 'safe' tests for emptyness.
->
->(eg if I test for a sphere of radius != -1.0, will I get into trouble if I scale
->the sphere with pfOrthoXformSphere and end up with a radius of -2.0. Is it OK
->to test for a negative radius?)
->
->Maybe these tests should be added to Performer in a future release.

Yes.

src.

-- 
-----{-----{---++at++   -----{----{---++at++   -----{----{---++at++   -----{----{---++at++
Sharon Rose Clay (Fischler) - Silicon Graphics, Advanced Systems Dev.
src++at++sgi.com  (415) 933 - 1002  FAX: (415) 965 - 2658  MS 8U-590
http://www.sgi.com/Technology/Performer/
-----{-----{---++at++   -----{----{---++at++   -----{----{---++at++   -----{----{---++at++


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