HTML5 Canvas Drawing on both Desktop Computer & Smart Phones

In this post I am going to show a simple example to respond touch and mouse events to draw on both desktop computer as well as iPad, iPhone or any other touch phones using canvas.

Demo
This browser does not supports canvas.

Code Section
HTML Canvas Code
<canvas height="300" id="drawing" width="400">This browser does not supports canvas.</canvas>
JavaScript Code

var cb_canvas = null;
var cb_ctx = null;
var cb_lastPoints = null;
var cb_easing = 0.4;

// Setup event handlers
window.onload = init;
function init(e) {
 cb_canvas = document.getElementById("cbook");

 cb_lastPoints = Array();

 if (cb_canvas.getContext) {
  cb_ctx = cb_canvas.getContext('2d');
  cb_ctx.lineWidth = 20;
  cb_ctx.strokeStyle = "rgb(255, 255, 0)";
  cb_ctx.lineCap = 'round';
  cb_ctx.beginPath();

  cb_canvas.onmousedown = startDraw;
  cb_canvas.onmouseup = stopDraw;
  cb_canvas.ontouchstart = startDraw;
  cb_canvas.ontouchstop = stopDraw;
  cb_canvas.ontouchmove = drawMouse;
 }
}

function startDraw(e) {
 if (e.touches) {
  // Touch event
  for (var i = 1; i <= e.touches.length; i++) {
   cb_lastPoints[i] = getCoords(e.touches[i - 1]); // Get info for finger #1
  }
 }
 else {
  // Mouse event
  cb_lastPoints[0] = getCoords(e);
  cb_canvas.onmousemove = drawMouse;
 }
 
 return false;
}

// Called whenever cursor position changes after drawing has started
function stopDraw(e) {
 e.preventDefault();
 cb_canvas.onmousemove = null;
}

function drawMouse(e) {
 if (e.touches) {
  // Touch Enabled
  for (var i = 1; i <= e.touches.length; i++) {
   var p = getCoords(e.touches[i - 1]); // Get info for finger i
   cb_lastPoints[i] = drawLine(cb_lastPoints[i].x, cb_lastPoints[i].y, p.x, p.y);
  }
 }
 else {
  // Not touch enabled
  var p = getCoords(e);
  cb_lastPoints[0] = drawLine(cb_lastPoints[0].x, cb_lastPoints[0].y, p.x, p.y);
 }
 cb_ctx.stroke();
 cb_ctx.closePath();
 cb_ctx.beginPath();

 return false;
}

// Draw a line on the canvas from (s)tart to (e)nd
function drawLine(sX, sY, eX, eY) {
 cb_ctx.moveTo(sX, sY);
 cb_ctx.lineTo(eX, eY);
 return { x: eX, y: eY };
}

// Get the coordinates for a mouse or touch event
function getCoords(e) {
 if (e.offsetX) {
  return { x: e.offsetX, y: e.offsetY };
 }
 else if (e.layerX) {
  return { x: e.layerX, y: e.layerY };
 }
 else {
  return { x: e.pageX - cb_canvas.offsetLeft, y: e.pageY - cb_canvas.offsetTop };
 }
}