Bug 6749

$(mesasrc)/glu/sgi/libutil/project.c:__gluInvertMatrixd:This algorithm is wrong

The inverse matrix of identity matrix is itself!

but old __gluInvertMatrixd consider identity matrix is bad matrix.

modified:

/*
** inverse = invert(src)
*/
static int __gluInvertMatrixd(const GLdouble src[16], GLdouble inverse[16])
{
    int i, j, k;
    double t;
    GLdouble temp[4][4];

    for (i=0; i<4; i++) {
	for (j=0; j<4; j++) {
	    temp[i][j] = src[i*4+j];
	}
    }
    __gluMakeIdentityd(inverse);

    for (i = 0; i < 4; i++) {
	if (temp[i][i] == 0.0f) {
	    /*
	    ** Look for non-zero element in column
	    */
	    for (j = i + 1; j < 4; j++) {
		if (temp[j][i] != 0.0f) {
		    break
		}
	    }
	
	    if (j != 4) {
		/*
		 ** Swap rows.
		 */
		for (k = 0; k < 4; k++) {
		    t = temp[i][k];
		    temp[i][k] = temp[j][k];
		    temp[j][k] = t;
	
		    t = inverse[i*4+k];
		    inverse[i*4+k] = inverse[j*4+k];
		    inverse[j*4+k] = t;
		}
	    }
	    else {
		/*
		** No non-zero pivot.  The matrix is singular, which shouldn't
		** happen.  This means the user gave us a bad matrix.
		*/
		return GL_FALSE;
	    }
	}

	t = 1.0f / temp[i][i];
	for (k = 0; k < 4; k++) {
	    temp[i][k] *= t;
	    inverse[i*4+k] *= t;
	}
	for (j = 0; j < 4; j++) {
	    if (j != i) {
		t = temp[j][i];
		for (k = 0; k < 4; k++) {
		    temp[j][k] -= temp[i][k]*t;
		    inverse[j*4+k] -= inverse[i*4+k]*t;
		}
	    }
	}
    }
    return GL_TRUE;
}