class Trail {
  //---------------
  float[] x, y, z;  // position
  int firstIndex;
  color clr;
  //---------------
  Trail(float ix, float iy, float iz, int len, color clr){
    firstIndex = 0;
    x = new float[len];
    y = new float[len];
    z = new float[len];
    for(int i=0;i<x.length;i++){
      x[i] = ix;
      y[i] = iy;
      z[i] = iz;
    }
    this.clr = color( red(clr)/2, green(clr)/2, blue(clr)/2 );
  }
  //---------------
  void update(float ix, float iy, float iz){
      x[firstIndex] = ix;
      y[firstIndex] = iy;
      z[firstIndex] = iz;
      firstIndex = (firstIndex+1) % x.length;
  }
  //---------------
  void visualize(){
    stroke(clr);
    beginShape(LINE_STRIP);
    for(int i=firstIndex;i<x.length;i++)
      vertex(x[i],y[i],z[i]);
    for(int i=0;i<firstIndex;i++)
      vertex(x[i],y[i],z[i]);
    endShape();
  }
  //---------------
}