Re: problem with pfMatrix

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Angus Dorbie (dorbie++at++sgi.com)
Tue, 01 Jun 1999 12:42:08 -0700

Your code is working correctly. The child values shouldn't change. The
transformation is relative to the parent. The cumulative effects of the
transformation are applied in the modelview matrix (but that includes
the viewing xform too).

To get the combined matrix of parent and child you'd need to read them
both and multiply those matrices together in the right order.

In your case, to position the channel at the eye, you need to multiply
the left and right eyes with the head matrix yourself. Performer does
not expose this, it DOES draw the right thing.

Cheers,Angus.

Torbjörn Håkansson wrote:
>
> Hi all pf Users
>
> I have a problem with pfMatrix, I wonder why the Matrix's value don't change when I rotate or translate the parent pfDCS, the parent pfDCS is moved by input data from a sensor in a Flock of Birds, the child in my model shall represent two eyes, I thought that performer did the matrix multiplication automatically
>
> Thanks in advance !
>
> -------------------------------------------------------------------------
> Code example !!
>
> pfDCS *Head; // attached to Flock of Bird Sensor
> pfDCS *L_Eye;
> pfDCS *R_Eye;
>
> pfCoord CamSens;
> pfCoord HandSens;
> pfMatrix L_EyeMat ;
> pfMatrix R_EyeMat ;
>
> L_Eye = new pfDCS;
> R_Eye = new pfDCS;
> Head = new pfDCS;
>
> Head->addChild(L_Eye);
> Head->addChild(R_Eye);
>
>
> L_Eye->setTrans(-0.50f,0.0f,0.0f);
> R_Eye->setTrans(0.50f,0.0f,0.0f);
>
> float alfa = 0.0f
>
>
> while(exitFlag)
> {
> alfa++;
>
> getSensorData(); // my code to fetch FOB sensor data
>
> Head->setRot(0.50f*alfa,0.0f,0.0f);
>
> L_Eye->getMat ( L_EyeMat ); // why does this Matrix dont change value ?
> R_Eye->getMat ( R_EyeMat ); // why does this Matrix dont change value ?
>
> chan0->setViewMat( L_EyeMat );
> chan1->setViewMat( R_EyeMat );
>
> pfFrame();
>
> }
>
> ********************************************************************
> Torbjörn Håkansson
>
> URL: http://www.hbg.lth.se/~m96tha
> Mail : torbjorn.hakansson++at++telia.com
> Phone: +46-(0)40-320595
> ICQ: 281022
> ********************************************************************
>
> -----------------------------------------------------------------------
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