[Plib-users] R: R: culling problems w/ off-axis projection

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John,

Please find attached the patch.

This patch also include a fix to the function sgQuatToAxisAngle which
manages cases of Quat's W outside the range [-1:1] (acos undefined). For
this I used _isnan and _finite functions in MS Visual C++, whose
availability I ask all of you to verify on other Plib-supported platforms.
Otherwise just ignore this second part of the patch.

Thanks a lot,

Paolo Leoncini

> -----Messaggio originale-----
> Da: Fay, John F Dr CTR USAF AFMC 46 SK 
> [mailto:joh...@eg...] 
> Inviato: sabato 17 aprile 2010 18.33
> A: PLIB Users
> Oggetto: Re: [Plib-users] R: culling problems w/ off-axis projection
> 
> Paolo,
> 
> 	Congratulations and very good on having solved the 
> problem.  Is there a code change that you want me to put into 
> Subversion?
> 
> Dr. John F. Fay
> Technical Fellow
> Jacobs Technology TEAS Group
> 850-883-1294
> 
> 
> -----Original Message-----
> From: Paolo Leoncini [mailto:p.l...@ci...]
> Sent: Monday, April 12, 2010 3:21 AM
> To: 'PLIB Users'
> Subject: [Plib-users] R: culling problems w/ off-axis projection
> 
> Dear friends,
> 
> I think to have solved the problem.
> 
> > -----Messaggio originale-----
> > Da: p.l...@ci... [mailto:p.l...@ci...]
> > Inviato: martedì 6 aprile 2010 11.19
> > A: pli...@li...
> > Oggetto: [Plib-users] culling problems w/ off-axis projection
> > 
> > Dear all,
> > 
> > I'm doing off-axis projection (the most general form of
> > projection) by translating the four corners of the screen into a 
> > projection matrix, for which I added a new method to the sgFrustum 
> > class and to the Context too. The only difference with 
> giving the six 
> > frustum extrema values is that no calculation occurs. 
> Culling seems to 
> > rely only on the projection matrix values, so, apparently, no 
> > difference w/ the on-axis standard case.
> > 
> > As far as the projection is not far from the on-axis case 
> the culling 
> > gives no problem. Instead when screen position definition 
> results in a 
> > large rotation in the projection matrix objects suddenly 
> disappear and 
> > reappear by apparently no rule.
> > 
> > Are culling calculations based on a particular form of the 
> projection 
> > matrix?
> > should culling planes be extracted in a different way to 
> support the 
> > more general case?
> 
> In sgFrustum::contains( const sgSphere *s ) (sg.cxx), the for 
> the non-ortho case which is presently done this way:
> 
>     sp1 = plane[ SG_LEFT_PLANE  ][0] * center[0] + plane[ 
> SG_LEFT_PLANE ][2] * center[2] ;
>     sp2 = plane[ SG_RIGHT_PLANE ][0] * center[0] + plane[ 
> SG_RIGHT_PLANE ][2] * center[2] ;
>     sp3 = plane[ SG_BOT_PLANE   ][1] * center[1] + plane[ SG_BOT_PLANE
> ][2] * center[2] ;
>     sp4 = plane[ SG_TOP_PLANE   ][1] * center[1] + plane[ SG_TOP_PLANE
> ][2] * center[2] ;
> 
> should be substituted by the following general form:
> 
>     sp1 = sgScalarProductVec3 ( plane[ SG_LEFT_PLANE  ], 
> center ) + plane[ SG_LEFT_PLANE  ][3] ;
>     sp2 = sgScalarProductVec3 ( plane[ SG_RIGHT_PLANE ], 
> center ) + plane[ SG_RIGHT_PLANE ][3] ;
>     sp3 = sgScalarProductVec3 ( plane[ SG_BOT_PLANE   ], 
> center ) + plane[
> SG_BOT_PLANE   ][3] ;
>     sp4 = sgScalarProductVec3 ( plane[ SG_TOP_PLANE   ], 
> center ) + plane[
> SG_TOP_PLANE   ][3] ;
> 
> The hint were just below there (see comment "Note: in the 
> general case, we would have to do:").
> I propose to patch it since this general form also manages 
> the default on-axis case, but Steve should definitely give 
> the go-ahead.
> Should someone be concerned about performances I could supply 
> a bit larger patch for introducing the ability to supply the 
> Context a general perspective matrix, so to have the general 
> case only calculated in this eventuality.
> 
> > Thanks a lot,
> > 
> > Paolo Leoncini
> 
> Thanks in advance to a good will updater (John, it's you as usual?).
> 
> Paolo Leoncini
> 
> 
> > --------------------------------------------------------------
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> 
> 
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> ----------------
> Download Intel&#174; Parallel Studio Eval Try the new 
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> proactively, and fine-tune applications for parallel performance.
> See why Intel Parallel Studio got high marks during beta.
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