let i = 0;

let continued = false;

let offset = 0;

const incrementSpeed = 50;

​

function setup() {

  createCanvas(400, 400);

  // frameRate(120);

  background(220)

}

​

function draw() {

  // background(220);

  if (i > width && continued == false) {

    continued = true;

    i = 0;

    i = offset;

    line(0,height-i,width,i);

    offset++;

  return;

  } else if (i > height && continued == true) {

    continued = false;

    i = offset;

    offset++;

  }

  if (!continued) {

    line(i,0,width-i,height);

    i += incrementSpeed;

  } else {

    line(0,height-i,width,i);

    i += incrementSpeed;

  }

}