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

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John, 

> -----Messaggio originale-----
> Da: John F. Fay [mailto:joh...@cy...] 
> Inviato: sabato 29 maggio 2010 4.15
> A: PLIB Users
> Oggetto: Re: [Plib-users] R: R: culling problems w/ off-axis 
> projection
> 
> Paolo,
> Message-Id: <201...@yo...>
> 
>          Please pardon my delay in answering; May is never a 
> good month for me.  Did this patch get put in already,

No.

> or did the patch file switch the "from" and "to" versions?

Yes.

>                  - John

Thanks for taking care of it.

Greetings,

Paolo

> At 09:40 AM 4/21/2010, you wrote:
> >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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