class Trail2D {
  //---------------
  float[] x, y;  // position
  int firstIndex;
  int timer;
  int density;
  color clr;
  //---------------
  Trail2D(float ix, float iy, int len, int dens, color clr){
    firstIndex = 0;
    x = new float[len/dens];
    y = new float[len/dens];
    timer = 0;
    density = dens;
    for(int i=0;i<x.length;i++){
      x[i] = ix;
      y[i] = iy;
    }
    this.clr = clr;
  }
  //---------------
  void update(float ix, float iy){
    timer++;
    if(timer == density){
      firstIndex = (firstIndex+1) % x.length;
      timer = 0;
    }
    x[firstIndex] = ix;
    y[firstIndex] = iy;
  }
  //---------------
  void visualize(){
    stroke(clr);
    beginShape(LINE_STRIP);
    for(int i=firstIndex+1;i<x.length;i++)
      vertex(x[i],y[i]);
    for(int i=0;i<=firstIndex;i++)
      vertex(x[i],y[i]);
    endShape();
  }
  //---------------
}