var canvas = document.getElementById('signature-pad');

// Adjust canvas coordinate space taking into account pixel ratio,
// to make it look crisp on mobile devices.
// This also causes canvas to be cleared.

function resizeCanvas() {
  // When zoomed out to less than 100%, for some very strange reason,
  // some browsers report devicePixelRatio as less than 1
  // and only part of the canvas is cleared then.
  var ratio = Math.max(window.devicePixelRatio || 1, 1);
  canvas.width = canvas.offsetWidth * ratio;
  canvas.height = canvas.offsetHeight * ratio;
  canvas.getContext('2d').scale(ratio, ratio);
}

if (canvas) {
  window.onresize = resizeCanvas;
  resizeCanvas();
}

var signaturePad = new SignaturePad(canvas, {
  backgroundColor: 'rgb(255, 255, 255)', // necessary for saving image as JPEG; can be removed is only saving as PNG or SVG
});

document.getElementById('save-png').addEventListener('click', function () {
  if (signaturePad.isEmpty()) {
    return alert('Please provide a signature first.');
  }

  var data = signaturePad.toDataURL('image/png');
  console.log(data);
});

document.getElementById('clear').addEventListener('click', function () {
  signaturePad.clear();
});

document.getElementById('draw').addEventListener('click', function () {
  var ctx = canvas.getContext('2d');
  console.log(ctx.globalCompositeOperation);
  ctx.globalCompositeOperation = 'source-over'; // default value
});

document.getElementById('erase').addEventListener('click', function () {
  var ctx = canvas.getContext('2d');
  ctx.globalCompositeOperation = 'destination-out';
});