/** Vector in 3 dimensions */
import java.lang.*;

public class Vec3 {
  float x1=(float)0.0,x2=(float)0.0,x3=(float)0.0;
 
  /** Simply creates instance, components initialised to 
        <tt>(float)0.0</tt> */
  public Vec3() {
    //vector already set to (0.0,0.0,0.0)
  }
 
  public Vec3(float xx1, float xx2, float xx3) {
    x1=xx1; 
    x2=xx2; 
    x3=xx3;
  }

  public void setValue(float xx1, float xx2, float xx3) {
    x1=xx1; 
    x2=xx2; 
    x3=xx3;
  }

  public void setValue(Vec3 a) {
    x1=a.x1; 
    x2=a.x2; 
    x3=a.x3;
  }

  public void setValueRelative(float xx1, float xx2, float xx3) {
    x1=x1+xx1; 
    x2=x2+xx2; 
    x3=x3+xx3;
  }


  /** Sets <tt>Vec3 this</tt> to zero */
  public void setZero() {
    x1=(float)0.0; 
    x2=(float)0.0; 
    x3=(float)0.0;
  }


  /** Add and accumulate. <tt>Vec3 a</tt> is added to 
      <tt>Vec3 this</tt> */
  public void accAdd(Vec3 a) {
    x1=x1+a.x1;
    x2=x2+a.x2;
    x3=x3+a.x3;
  }
  
  
  /** Subtract and accumulate. <tt>Vec3 a</tt> is subtracted from 
      <tt>Vec3 this</tt> */
  public void accSub(Vec3 a) {
    x1=x1-a.x1;
    x2=x2-a.x2;
    x3=x3-a.x3;
  }
  
  public static float dot(Vec3 a, Vec3 b) {
    return(a.x1*b.x1+a.x2*b.x2+a.x3*b.x3);
  }
 
  public void cross(Vec3 a, Vec3 b) {
    x1=a.x2*b.x3-a.x3*b.x2;
    x2=a.x3*b.x1-a.x1*b.x3;
    x3=a.x1*b.x2-a.x2*b.x1;
  }

  public void normal(Vec3 a, Vec3 b) {
    // this is normal to a and b
    float length;
    x1=a.x2*b.x3-a.x3*b.x2;
    x2=a.x3*b.x1-a.x1*b.x3;
    x3=a.x1*b.x2-a.x2*b.x1;
    length=this.length();
    x1=x1/length;
    x2=x2/length;
    x3=x3/length;    
  }

  /** Calculate unit normal to triangle given by position vectors a, b
  and c in the sense that a->b->c goes right-handed around n. For 
  example, if a, b and c are clockwise and flat in the plane
  of view, n is away from the viewer.<p>
  Alternatively, this is (b-a) cross (c-a) normalised. 
  */
  public void normal(Vec3 a, Vec3 b, Vec3 c) {
    float length;
    x1=(b.x2-a.x2)*(c.x3-a.x3)-(b.x3-a.x3)*(c.x2-a.x2);
    x2=(b.x3-a.x3)*(c.x1-a.x1)-(b.x1-a.x1)*(c.x3-a.x3);
    x3=(b.x1-a.x1)*(c.x2-a.x2)-(b.x2-a.x2)*(c.x1-a.x1);
    length=this.length();
    x1=x1/length;
    x2=x2/length;
    x3=x3/length;    
  }

  public void normalise(Vec3 a) {
    float length;
    length=a.length();
    a.x1=a.x1/length;
    a.x2=a.x2/length;
    a.x3=a.x3/length;
  }

  /** Returns length of vector */
  public float length() {
    return((float)Math.sqrt(x1*x1+x2*x2+x3*x3));
  }

  /** Returns length of vector squared */
  public float lengthSqd() {
    return(x1*x1+x2*x2+x3*x3);
  }
  
  
  /** Returns length of vector (b-a) squared */
  public static float distSqd(Vec3 a, Vec3 b) {
    return((float)(a.x1-b.x1)*(a.x1-b.x1)+
                  (a.x2-b.x2)*(a.x2-b.x2)+
                  (a.x3-b.x3)*(a.x3-b.x3));
  }

}