Creating GL MVIEWING matrix from Performer's model and view matrices?

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Nicolas Gauvin (nicolas++at++cae.ca)
Thu, 1 Aug 1996 12:21:52 -0400

I'm trying without success to create the IRIS GL model/view (MVIEWING) matrix
from Performer's model matrix and viewing matrix (which are kept seperate).

In a node draw callback I get the Performer matrices by doing this:

pfGetModelMat(modelMat);
pfGetViewMat(viewMat);

After pfDraw is finished I want to recreate the exact same MVIEWING GL matrix
that was in effect during the node draw callback.

So I tried doing something like this:

// first take into account the change in coordinate system from Performer
// to IRISGL which is a rotation of -90 degrees around the X axis
pfMatrix rot;
rot.makeRot(-90.0f,1.0f,0.0f,0.0f);

pfMatrix mat;
// multiply all the matrices together
mat = rot * modelMat * viewMat;

// set this matrix as the IRIS GL ModelView matrix
mmode(MVIEWING);
pfLoadMatrix(mat);

...then draw my own stuff

Obviously I'm doing something wrong because it is not working as espected.
The final matrix is different than the one that was in effect during the draw
callback (I compared them). I've tried switching the order of multiplication
without improvements.

If instead of saving the Performer's matrices in the draw callback I save
the current GL MVIEWING matrix by doing:

getmatrix(glMat);

and then restoring it later with:

mmode(MVIEWING);
loadmatrix(glMat);

It works.

The problem is that is not a satisfactory solution for my application.
I really need to be able re-create the MVIEWING matrix from Performer's
internal matrices.

I'm sure other people have tried this before so any help would be appreciated.

I suspect that Performer builds the MVIEWING matrix in a different way than
I'm expecting.

-- 
Nicolas Gauvin			CAE Electronics Ltd., 8585 Cote De Liesse
Software Developer 		Saint-Laurent, Quebec, Canada, H4L-4X4
3-D Graphics Applications	tel: +1 514 341 2000 extension 2275
nicolas++at++cae.ca			fax: +1 514 340 5496
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