Re: Performer & color_matrix_SGI
Brian Furtaw (brian++at++sgi.com)
Wed, 29 Jan 1997 10:32:08 -0500
On Jan 29, 2:00pm, Harri Kaimio wrote:
> Subject: Performer & color_matrix_SGI
> Hi all Performer gurus!
>
> I am afraid I have lost all hope of understanding, how Performer works
> internally :-(
>
> I am working on a project in which I need to change the color saturation
> (perhaps also hue) of part of the scene graph over time. The way I have
> planned to do it is by using the color matrix OpenGL extension. My
> source code looks like this:
>
>
> int
> bwPreDraw( pfTraverser * )
> {
> // draw callback to turn on color matrix stuff
> float colorMat[16];
>
> // set up the color matrix
> ...
>
> // Store current matrix mode
> int mmode[1];
> glGetIntegerv( GL_MATRIX_MODE, mmode );
>
> glMatrixMode( GL_COLOR );
> glLoadMatrixf( colorMat );
> glMatrixMode( mmode[0] );
> return PFTRAV_CONT;
> }
>
> int
> bwPostDraw( pfTraverser * )
> {
> // Turn off color matrixes
> int mmode[1];
> glGetIntegerv( GL_MATRIX_MODE, mmode );
> glMatrixMode( GL_COLOR );
>
> glLoadIdentity();
> glMatrixMode( mmode[0] );
> return PFTRAV_CONT;
> }
>
> ...
>
> // Set color matrix callbacks for a node
> node->setTravFuncs( PFTRAV_DRAW, bwPreDraw, bwPostDraw )
>
> ...
>
> OK, this kind of works - I can specify different color matrix for
> different nodes and the results look correct, BUT I CANNOT ANIMATE THE
> COLOR MATRIXES. If I change the color matrix used for a certain object
> between frames, it makes no visible difference in the rendered picture -
> it is always rendered using the color matrices specified in the first
> frame of simulation. I have checked that my callbacks are really called
> and correct color matrixes have been loaded for each frame.
>
> Can someone wiser than me explain what is happening? The only
> explanation I can think of is that perhaps Performer stores my database
> into a GL display list during the first frame, so my color matrices are
> also stored there. I is so? And what would be the best way around this
> problem?
>
> Of course I could render the scene twice, the second time with B/W
> textures, but I am not very fond of that idea (twice the geometry, twice
> the textures, more difficult to use as a "plug-and-play" routine,
> difficulties in using transparent objects...)
>
> I would greatly appreciate any help on this.
> --
> -----------------------------------------------------------------
> Harri Kaimio | harri.kaimio++at++yle.fi
> Computer Graphics Specialist | http://cartes.hut.fi/~hkaimio
> Finnish Broadcasting Company | Tel. +358-40-50 67 679
> TV Production Operations | Fax. +358-0-1480 4769
> =======================================================================
> List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/
> Submissions: info-performer++at++sgi.com
> Admin. requests: info-performer-request++at++sgi.com
>-- End of excerpt from Harri Kaimio
Harri,
to find out how performer works get a hold of the 1994 SIGGRAPH Proceedings
and read "IRIS Performer: A High Performance Multiprocessing Toolkit for
Real-Time 3D Graphics" should help your understanding greatly.
Brian
--
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Brian Furtaw (brian++at++sgi.com)
VisSim Technical Consultant
12200-G Plum Orchard Drive Office:(301)572-3293 Fax: (301)872-3293
Silver Spring, Maryland 20904 OpenGL/ImageVision/OpenInventor/Performer
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