Re: BACK_TO_FRONT sorting and 'Inverse Singular Matrix'

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Angus Dorbie (dorbie++at++sgi.com)
Wed, 06 Jan 1999 18:00:47 -0800

Angus Dorbie wrote:
>
> You sure there isn't a culprit DCS in the graph with a singular matrix,
> for example shadows on the ground with a zero scaling factor in Z?
>
> FYI this would cause z fighting which wouldn't be solved by sorting.
> It's a different class of problem.
>
> What machine are you using?
>
> Also for sort to look good you need the objects with transparency to be
> split up at the granularity of potential occlusion. Sorting only happens
> on geosets so objects which potentially occlude each other need to be is
                                                                      
in^^

> separate geosets. You chould also consider the centroid & size of these
> objects, a simple depth sort will not work if objects overlap
> significantly on some axis w.r.t. their rize
                                     size ^^^^

>
> Cheers,Angus.
>
> Greg Harrison wrote:
> >
> > When we switched our program from PFSORT_BY_STATE to PFSORT_BACK_TO_FRONT
> > (because of overlapping MS_ALPHA transparency), we get a pf error about
> > 'Inverse Singular Matrix' when there are many objects in the scene (many DCS
> > nodes). I'm aware of the pfChannel man page caveat, "
> >
> > However, range sorting spans both transformation and draw callback
> > boundaries. Thus a range-sorted scene graph with many transformations and
> > expensive draw callbacks may suffer reduced performance due to an increased
> > number of transformation and draw callback changes."
> >
> > Unfortunately, the singular matrices don't seem to go away when the view is
> > reduced and the eat up an inordinate amount of CPU time (exception
> > handling?). Fortunately the scene is still drawn properly. Is there any
> > solution, short of "fewer DCS nodes in view"? GL_BLEND transparency and
> > using the opaque and transparen bins is not an option since it's too
> > expensive. Anyone hit this before?
> >
> > Greg Harrison
> > Air Force Institute of Technology
> >
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>
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"Only the mediocre are always at their best." -- Jean Giraudoux 


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