function renderCartPole(cartPole, canvas) {
  if (!canvas.style.display) {
    canvas.style.display = 'block';
  }
  const X_MIN = -cartPole.xThreshold;
  const X_MAX = cartPole.xThreshold;
  const xRange = X_MAX - X_MIN;
  const scale = canvas.width / xRange;

  const context = canvas.getContext('2d');
  context.clearRect(0, 0, canvas.width, canvas.height);
  const halfW = canvas.width / 2;

  // Draw the cart.
  const railY = canvas.height * 0.8;
  const cartW = cartPole.cartWidth * scale;
  const cartH = cartPole.cartHeight * scale;

  const cartX = cartPole.x * scale + halfW;

  context.beginPath();
  context.strokeStyle = '#000000';
  context.lineWidth = 2;
  context.rect(cartX - cartW / 2, railY - cartH / 2, cartW, cartH);
  context.stroke();

  // Draw the wheels under the cart.
  const wheelRadius = cartH / 4;
  for (const offsetX of [-1, 1]) {
    context.beginPath();
    context.lineWidth = 2;
    context.arc(
        cartX - cartW / 4 * offsetX, railY + cartH / 2 + wheelRadius,
        wheelRadius, 0, 2 * Math.PI);
    context.stroke();
  }

  // Draw the pole.
  const angle = cartPole.theta + Math.PI / 2;
  const poleTopX =
      halfW + scale * (cartPole.x + Math.cos(angle) * cartPole.length);
  const poleTopY = railY -
      scale * (cartPole.cartHeight / 2 + Math.sin(angle) * cartPole.length);
  context.beginPath();
  context.strokeStyle = '#ffa500';
  context.lineWidth = 6;
  context.moveTo(cartX, railY - cartH / 2);
  context.lineTo(poleTopX, poleTopY);
  context.stroke();

  // Draw the ground.
  const groundY = railY + cartH / 2 + wheelRadius * 2;
  context.beginPath();
  context.strokeStyle = '#000000';
  context.lineWidth = 1;
  context.moveTo(0, groundY);
  context.lineTo(canvas.width, groundY);
  context.stroke();

  const nDivisions = 40;
  for (let i = 0; i < nDivisions; ++i) {
    const x0 = canvas.width / nDivisions * i;
    const x1 = x0 + canvas.width / nDivisions / 2;
    const y0 = groundY + canvas.width / nDivisions / 2;
    const y1 = groundY;
    context.beginPath();
    context.moveTo(x0, y0);
    context.lineTo(x1, y1);
    context.stroke();
  }

  // Draw the left and right limits.
  const limitTopY = groundY - canvas.height / 2;
  context.beginPath();
  context.strokeStyle = '#ff0000';
  context.lineWidth = 2;
  context.moveTo(1, groundY);
  context.lineTo(1, limitTopY);
  context.stroke();
  context.beginPath();
  context.moveTo(canvas.width - 1, groundY);
  context.lineTo(canvas.width - 1, limitTopY);
  context.stroke();
}
Render the current state of the system on an HTML canvas.

@param {CartPole} cartPole The instance of cart-pole system to render.
@param {HTMLCanvasElement} canvas The instance of HTMLCanvasElement on which
  the rendering will happen.