Re: [Plib-devel] [Plib-users] R: R: culling problems w/ off-axis projection
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Re: [Plib-devel] [Plib-users] R: R: culling problems w/ off-axis projection
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From: John F. F. <joh...@cy...> - 2010-05-31 12:35:53
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Gentlemen,
I have just put the below-mentioned
patch into PLIB. It uses the functions
"_isnan" and "_isfinite" which are just fine on
my Windows/MSVC platform. Please check it out on
other platforms and let me know of any problems.
- John
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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> > >
> >
> >
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>
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