/* Auteur: Nicolas JANEY                                */
/* nicolas.janey@univ-fcomte.fr                         */
/* Novembre 2006                                        */
/* Transformation geometrique en coordonnees homogenes  */
/* pour un changement de repere de type repere global   */
/* vers repere observateur avec l'axe (0.0,1.0,0.0)     */
/* vertical en coordonnees observateur                  */

public class LookAt extends Transformation {

  public LookAt(float pox,float poy,float poz,
                float pvx,float pvy,float pvz) throws ArithmeticException {
    super();
    remplissage(pox,poy,poz,pvx,pvy,pvz);
  }

  public LookAt(Position po,Position pv) throws ArithmeticException {
    super();
    remplissage(po.getX(),po.getY(),po.getZ(),
                pv.getX(),pv.getY(),pv.getZ());
  }

  private void remplissage(float pox,float poy,float poz,
                           float pvx,float pvy,float pvz) throws ArithmeticException {
    float nx = pvx-pox;
    float ny = pvy-poy;
    float nz = pvz-poz;
    float d =(float) Math.sqrt(nx*nx+ny*ny+nz*nz);
    if ( d == 0 ) {
      throw new ArithmeticException(); }
    nx /= d;
    ny /= d;
    nz /= d;
    float a = 1.0F/(float) Math.sqrt(1.0F-ny*ny);
    this.c[0][0] = -a*nz;
    this.c[0][2] = a*nx;
    this.c[0][3] = a*(pox*nz-poz*nx);
    this.c[1][0] = -a*nx*ny;
    this.c[1][1] = 1.0F/a;
    this.c[1][2] = -a*ny*nz;
    this.c[1][3] = a*ny*(pox*nx+poz*nz)-poy/a;
    this.c[2][0] = -nx;
    this.c[2][1] = -ny;
    this.c[2][2] = -nz;
    this.c[2][3] = pox*nx+poy*ny+poz*nz;
  }
}