Path: chuka.playstation.co.uk!news
From: "Michael Enoch" <100413.2514@compuserve.com>
Newsgroups: scee.yaroze.programming.libraries
Subject: Re: Rotation Matrix Functions : The Solution?
Date: 14 Apr 1997 23:04:05 GMT
Organization: PlayStation Net Yaroze (SCEE)
Lines: 179
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> Two things: 
> 
> firstly, your earlier postings gave printouts of a matrix;
> after some rotation, the matrix columns were blatantly not of
> size 4096, which the normalisation in code should guarantee.
> 
> secondly, object stretching is a Definite sign of matrix
> distortion; to sort this, please post your code for maintaining/
> re-normalising the matrix, AND that for doing the basic rotation.
> 
> Lewis
>

OK, I've reformated the code slightly to make it more readable.  It starts
at the comment with asterixes and ends at another.  If it seems familiar
then thats because I borrowed the basics from a demo program.  The matrix
fixing code I wrote is in the middle somewhere with a label so you can't
miss it.  You'll notice it fixes an object called ship[0] every time, this
is because I'm only working with one object at the moment and I just wanted
to see if it worked before making a final alteration to the function.  The
rsin() and rcos() functions are also borrowed from a demo, they just supply
sine and cosine values from tables(in the correct range to 4096).  I'm
fairly sure they are not faulty but I'm going to rewrite them anyway after
posting this just to be sure.
	Thanks, Mike.

//**************************************************************************
***************

void CalculateObjectPosition(MATRIX* GlobalMatrix,
					VECTOR* rotation,
					VECTOR* position,
					VECTOR* velocity,
					GsCOORDINATE2* coordSystem)
{	
      int i=0;
      u_long length;
	VECTOR realMovement;
	MATRIX xMatrix, yMatrix, zMatrix;
	MATRIX copy;

// velocity is object-relative, is firstly converted to 
// world-relative terms
// eg
// find the object-local velocity in super coordinate terms
        ApplyMatrixLV(GlobalMatrix, velocity, &realMovement);

// update position by super-relative movement
	position->vx += realMovement.vx;
	position->vy += realMovement.vy;
	position->vz += realMovement.vz;

      xMatrix=xrotmatrix(rotation->vx);
      yMatrix=yrotmatrix(rotation->vy);
      zMatrix=zrotmatrix(rotation->vz);

// to get world-relative rotations instead:
// use 
        MulMatrix0(GlobalMatrix, &xMatrix, &copy);
        MulMatrix0(&copy, &yMatrix, GlobalMatrix);
        MulMatrix0(GlobalMatrix, &zMatrix, &copy);

        *GlobalMatrix = copy;

//--------------------------Start of Matrix fix code  
// This function is in main(), ship[0] is a global structure,
// containing an object handler, a coord system and some
// vectors which I pass through as the function arguments.
if(ship[0].moved==1)
{
ship[0].moved=0;
i=0;
length=sqrt(
(ship[0].GlobalMatrix.m[i][0]*ship[0].GlobalMatrix.m[i][0])+   
(ship[0].GlobalMatrix.m[i][1]*ship[0].GlobalMatrix.m[i][1])+
(ship[0].GlobalMatrix.m[i][2]*ship[0].GlobalMatrix.m[i][2]));

ship[0].GlobalMatrix.m[i][0]=
	(ship[0].GlobalMatrix.m[i][0]*ONE)/length;
ship[0].GlobalMatrix.m[i][1]=
	(ship[0].GlobalMatrix.m[i][1]*ONE)/length;
ship[0].GlobalMatrix.m[i][2]=
	(ship[0].GlobalMatrix.m[i][2]*ONE)/length;

i=1;
length=sqrt(
(ship[0].GlobalMatrix.m[i][0]*ship[0].GlobalMatrix.m[i][0])+
(ship[0].GlobalMatrix.m[i][1]*ship[0].GlobalMatrix.m[i][1])+
(ship[0].GlobalMatrix.m[i][2]*ship[0].GlobalMatrix.m[i][2]));

ship[0].GlobalMatrix.m[i][0]=
	(ship[0].GlobalMatrix.m[i][0]*ONE)/length;
ship[0].GlobalMatrix.m[i][1]=
	(ship[0].GlobalMatrix.m[i][1]*ONE)/length;
ship[0].GlobalMatrix.m[i][2]=
	(ship[0].GlobalMatrix.m[i][2]*ONE)/length;

i=2;
length=sqrt(
(ship[0].GlobalMatrix.m[i][0]*ship[0].GlobalMatrix.m[i][0])+
(ship[0].GlobalMatrix.m[i][1]*ship[0].GlobalMatrix.m[i][1])+
(ship[0].GlobalMatrix.m[i][2]*ship[0].GlobalMatrix.m[i][2]));

ship[0].GlobalMatrix.m[i][0]=
	(ship[0].GlobalMatrix.m[i][0]*ONE)/length;
ship[0].GlobalMatrix.m[i][1]=
	(ship[0].GlobalMatrix.m[i][1]*ONE)/length;
ship[0].GlobalMatrix.m[i][2]=
	(ship[0].GlobalMatrix.m[i][2]*ONE)/length;
}
//------------------End of Matrix fix code


// copy GlobalMatrix
        coordSystem->coord = *GlobalMatrix;
	
// set position absolutely	
	coordSystem->coord.t[0] = position->vx;
	coordSystem->coord.t[1] = position->vy;
	coordSystem->coord.t[2] = position->vz;

// tell GTE that coordinate system has been updated
	coordSystem->flg = 0;
}

MATRIX xrotmatrix(int r)
{
        MATRIX tmp;

        tmp.m[0][0]=ONE;
		tmp.m[0][1]=0;
			tmp.m[0][2]=0;
        tmp.m[1][0]=0;
		tmp.m[1][1]=rcos(r);
			tmp.m[1][2]=-rsin(r);
        tmp.m[2][0]=0;
		tmp.m[2][1]=rsin(r);
			tmp.m[2][2]=rcos(r);

        return tmp;
}

MATRIX yrotmatrix(int r)
{
        MATRIX tmp;

        tmp.m[0][0]=rcos(r);
		tmp.m[0][1]=0;
			tmp.m[0][2]=rsin(r);
        tmp.m[1][0]=0;
		tmp.m[1][1]=ONE;
			tmp.m[1][2]=0;
        tmp.m[2][0]=-rsin(r);
		tmp.m[2][1]=0;
			tmp.m[2][2]=rcos(r);

        return tmp;
}

MATRIX zrotmatrix(int r)
{
        MATRIX tmp;

        tmp.m[0][0]=rcos(r);
		tmp.m[0][1]=-rsin(r);
			tmp.m[0][2]=0;
        tmp.m[1][0]=rsin(r);
		tmp.m[1][1]=rcos(r);
			tmp.m[1][2]=0;
        tmp.m[2][0]=0;
		tmp.m[2][1]=0;
			tmp.m[2][2]=ONE;

        return tmp;
}

 //*************************************************************************
*******************