let h = w;

let x0 = 0;

let y0 = 0;

let x1 = w;

let y1 = 0;

let x2 = w;

let y2 = h;

let x3 = 0;

let y3 = h;

​

let squares = [];

let maxIterations = 10000;

let counter = 0;

let epsilon = 0.05;

let highlightIndex = 0;

let changeDelay = 0.05;

let changeTimer = 0;

​

​

function setup()

{

  createCanvas(w, h);

  noFill();

  do

  {

    PushSquare();

  } while(TiltedSquare(0.0625) && counter <= maxIterations);

}

​

​

function draw()

{

  blendMode(BLEND);

  background(40);

  // highlightIndex = squares.length - 5;

  let highlightCount = 10;

  for (let i = 0; i < squares.length; ++i)

  {

    let square = squares[i];

    if (highlightIndex <= i && i < highlightIndex + highlightCount ||

        highlightIndex - squares.length <= i && i < highlightIndex - squares.length +

        highlightCount)

      DrawLitSquare(square);

    else

      DrawUnlitSquare(square);

  }

//   changeTimer += deltaTime / 1000;

//   if (changeTimer >= changeDelay)

//   {

//     highlightIndex = (highlightIndex + 1) % squares.length;

//     changeTimer = changeTimer % changeDelay;

//   }

  highlightIndex = (highlightIndex + 7) % squares.length;

}

​

​

function TiltedSquare(f)

{

  let tx = x1 - x0;

  let ty = y1 - y0;

  let dx = tx * f;

  let dy = ty * f;

  let dSq = dx * dx + dy * dy;

  if (dSq <= epsilon)

    return false;

  x0 += dx;

  y0 += dy;

  x1 -= dy;

  y1 += dx;

  x2 -= dx;

  y2 -= dy;

  x3 += dy;

  y3 -= dx;

  ++counter;

  return true;

}

​

​

function PushSquare()

{

  squares.push([x0, y0, x1, y1, x2, y2, x3, y3]);

}

​

​

function DrawUnlitSquare(square)

{

  blendMode(BLEND);

  strokeWeight(1);

  stroke(255, 8);

  quad(...square);

}

​

​

function DrawLitSquare(square)

{

  blendMode(ADD);

  let maxSpread = 200;

  let count = 8;

  let p = 8;

  for (let i = count; i > 0; --i)

  {

    let t = i / count;

    let internal = (1 - cos(PI * t)) / 2;

    let r = 1 - pow(internal, p);

    let g = 1 - pow(internal, p);

    let b = pow(1 - internal, p);

    strokeWeight(t * maxSpread);

    stroke(255 * r, 255 * g, 255 * b, 255 * b * 0.12);

    quad(...square);

  }

}

​

​

function keyPressed()

{

  if (keyCode === 32)

    TogglePause();

  if (keyCode === ENTER)

    Step();

}

​

​

function TogglePause()

{

  if (isLooping())

    Pause();

  else

    Unpause();

}

​

​

function Pause()

{

  noLoop();

}

​

​

function Unpause()

{

  loop();

}

​

​

function Step()

{

  if (isLooping())

    Pause();

  redraw();

}

​