Random bits of knowledge

var t;
var HALF_WIDTH;
var HALF_HEIGHT;
var OFFSET;

function keyPressed() {
  if (key != ' ') return;
  if (!fullscreen()) {
      fullscreen(true);
      background(0);
      if (width!=displayWidth || height!=displayHeight) {
        resizeCanvas(displayWidth,displayHeight);
      }
      HALF_WIDTH=min(width,height)/2;
      HALF_HEIGHT=HALF_WIDTH;
      if (width>height) OFFSET=(max(width,height)-min(width,height))/2;
      t=1;
      loop();
  } else {
    fullscreen(false);
  }
}


function x1(k) {
  return -sin(4*PI*k/1000);
}

function y1(k) {
  return -cos(2*PI*k/1000);
}

function x2(k) {
  return -0.5*sin(8*PI*k/1000);
}

function y2(k) {
  return -0.5*cos(4*PI*k/1000);
}

function setup() {
  createCanvas(displayWidth,displayHeight);
  stroke(255);
  background(0);
  noCursor();
  displayStartText();
}

function displayStartText() {
  var start_text="Space to start/stop";
  textFont("Courier");
  textSize(32);
  fill(255);
  text(start_text,0.5*(width-textWidth(start_text)),0.5*(height-16))
}

function draw() {
  if (!fullscreen) {
    return;
  }
  if (t==999) noLoop();
    translate(OFFSET+HALF_WIDTH,HALF_HEIGHT);
    line(HALF_WIDTH*x1(t),-HALF_HEIGHT*y1(t),
         HALF_WIDTH*x2(t),-HALF_HEIGHT*y2(t));
  t++;
}