let history = [];

  let width = 400;

  let zero_line = 200;

  let amplitude = 100;

  let margins = 50;

  let graph_step = 1;

  let time_step = 1;

  let memory = (width - 2 * margins) / graph_step;

  let t = 0;

  return function() {

    t = (1 + 20*t) / (20 - t);

    let ft = amplitude * 2*t / (1+t*t);

    history.push(zero_line + ft);

    if(history.length > memory) {

      history.shift();

    }

    beginShape();

    for(let x = 0; x < history.length; ++x) {

      vertex(x*graph_step + margins, history[x]);    

    }

    endShape();

  }  

}();

​

function setup() {

  createCanvas(400, 400);

  noFill();

}

​

function draw() {

  background(220);

  draw_wave();  

}