RE: [Plib-users] Problem with sgHPRfromVec3

[Dave M. <Dav...@dy...>]

If you want to build ssg camera views from direction vectors, you could try
using ssgSetCameraLookAt(eye,center,up);  It eventually calls this routine
in sg.cxx:

void sgMakeLookAtMat4 ( sgMat4 dst, const sgVec3 eye, const sgVec3 center,
const sgVec3 up )
{
  // Caveats:
  // 1) In order to compute the line of sight, the eye point must not be
equal
  //    to the center point.
  // 2) The up vector must not be parallel to the line of sight from the eye
  //    to the center point.

  /* Compute the direction vectors */
  sgVec3 x,y,z;

  /* Y vector = center - eye */
  sgSubVec3 ( y, center, eye ) ;

  /* Z vector = up */
  sgCopyVec3 ( z, up ) ;

  /* X vector = Y cross Z */
  sgVectorProductVec3 ( x, y, z ) ;

  /* Recompute Z = X cross Y */
  sgVectorProductVec3 ( z, x, y ) ;

  /* Normalize everything */
  sgNormaliseVec3 ( x ) ;
  sgNormaliseVec3 ( y ) ;
  sgNormaliseVec3 ( z ) ;

  /* Build the matrix */
#define M(row,col)  dst[row][col]
  M(0,0) = x[0];    M(0,1) = x[1];    M(0,2) = x[2];    M(0,3) = 0.0;
  M(1,0) = y[0];    M(1,1) = y[1];    M(1,2) = y[2];    M(1,3) = 0.0;
  M(2,0) = z[0];    M(2,1) = z[1];    M(2,2) = z[2];    M(2,3) = 0.0;
  M(3,0) = eye[0];  M(3,1) = eye[1];  M(3,2) = eye[2];  M(3,3) = 1.0;
#undef M
}