/* Auteur: Nicolas JANEY                                */
/* nicolas.janey@univ-fcomte.fr                         */
/* Octobre 2007                                         */

public class Sphere {
  public Position c;
  public float r;

  public Sphere() {
    c = new Position();
    r = 1.0F;
  }
  
  public Sphere(Position c,float r) {
    this.c = new Position(c);
    this.r = r;
  }
  
  public Sphere(Sphere s) {
    c = new Position(s.c);
    r = s.r;
  }
  
  public boolean existeIntersection(RayonLumineux rl) {
    float sx = rl.o.x - c.x;
    float sy = rl.o.y - c.y;
    float sz = rl.o.z - c.z;
    float a = rl.d.dx*rl.d.dx + rl.d.dy*rl.d.dy + rl.d.dz*rl.d.dz;
    float b = 2.0F*(rl.d.dx*sx + rl.d.dy*sy + rl.d.dz*sz);
    float c = sx*sx + sy*sy +sz*sz - r*r;
    float delta = b*b-4*a*c;
    if ( delta < 0.0F )
      return(false);
    if ( delta == 0 ) {
      float t = -b/2.0F/a;
      return( t >= 0.0F); } 
    float t1 = (-b-((float) Math.sqrt(delta)))/2.0F/a;
    if ( t1 >= 0 )
      return(true);
    float t2 = (-b+((float) Math.sqrt(delta)))/2.0F/a;
    return( t2 >= 0 );
  }

  private Position positionSurRayon(RayonLumineux rl,float t) {
    return(new Position(rl.d.dx*t+rl.o.x,
                        rl.d.dy*t+rl.o.y,
                        rl.d.dz*t+rl.o.z));
  }
  
  public Position premiereIntersection(RayonLumineux rl) {
    float sx = rl.o.x - c.x;
    float sy = rl.o.y - c.y;
    float sz = rl.o.z - c.z;
    float a = rl.d.dx*rl.d.dx + rl.d.dy*rl.d.dy + rl.d.dz*rl.d.dz;
    float b = 2.0F*(rl.d.dx*sx + rl.d.dy*sy + rl.d.dz*sz);
    float c = sx*sx + sy*sy +sz*sz - r*r;
    float delta = b*b-4*a*c;
    if ( delta < 0.0F )
      return(null);
    if ( delta == 0 ) {
      float t = -b/2.0F/a;
      if ( t >= 0.0F)
        return(positionSurRayon(rl,t));
        else
        return(null); }
    { float t = (-b-((float) Math.sqrt(delta)))/2.0F/a;
      if ( t >= 0 )
        return(positionSurRayon(rl,t)); }
    { float t = (-b+((float) Math.sqrt(delta)))/2.0F/a;
      if ( t >= 0 )
        return(positionSurRayon(rl,t)); }
    return(null);
  }
  
  public String toString() {
    return("["+c+","+r+"]");
  }
}