WindowsJS PNG exporter

windowsjs-exporter.js

window.title = "Hello!";
window.visible = true;

const monotonicDelta = createMonotonicFPSGenerator(60);

function requestMonotonicAnimationFrame(callback) {
  callback(monotonicDelta.next().value);
}

const canvas = window.canvas;
const generator = createLeftPaddedNumberGenerator(6, 0);

async function draw(delta = 0) {
  const cyan = "#023047";
  const red = "#eb005a";
  const orange = "darkorange";

  canvas.fillStyle = cyan;
  canvas.fillRect(0, 0, canvas.width, canvas.height);

  canvas.fillStyle = orange;
  const y = canvas.height / 2;
  const w = canvas.width;
  const t = Math.cos(delta / 300);
  const x = w / 2 + (w / 4) * t;
  canvas.save();
  canvas.translate(x, y);
  canvas.rotate((t * Math.PI) / 2);
  canvas.fillRect(-100, -100, 200, 200);
  canvas.restore();

  const screenshot = await canvas.encode();
  const filepath = File.cwd + "/" + generator.next().value + ".png";
  await File.write(filepath, screenshot);
  requestMonotonicAnimationFrame(draw);
}

// Start the animation.
requestMonotonicAnimationFrame(draw);

// Helper functions
/**
 * Creates a generator capable of delivering a time that increments monotonically using the `fps`
 * ellapsed time as discrete step.
 *
 * @example
 * ```javascript
 * const generator = createMonotonicFPSGenerator(60);
 * console.log(generator.next().value);
 * // 0
 * console.log(generator.next().value);
 * // 16.66667
 * ```
 *
 * @param {number} fps - Frames per seconds needed to calculat the frame execution time.
 * @param {number} start - Time from which to start the generator.
 */
function* createMonotonicFPSGenerator(fps = 60, start = 0) {
  const step = 1000 / fps;
  while (true) {
    yield start;
    start += step;
  }
}
/**
 * Creates a left padded number generator left padded to always have a length equal to `length`.
 *
 * @example
 * ```javascript
 * const generator = createLeftPaddedNumberGenerator(3, 0);
 * console.log(generator.next().value);
 * // 000
 * console.log(generator.nex().value);
 * // 001
 * ```
 *
 * @param {number} length - Fix length of the returning string.
 * @param {number} start - Start number fo the generator.
 */
function* createLeftPaddedNumberGenerator(length = 6, start = 0) {
  while (true) {
    yield String(start++).padStart(length, "0");
  }
}