HTML 5 Canvas - A Simple Paint Program (Touch and Mouse)

gardnerp

3.67/5 (3 votes)

26 Apr 2012CPOL

164.9K

This is an alternative for HTML 5 Canvas - A Simple Paint Program

Introduction

I've seen quite a few HTML5 canvas painting examples, but I had not seen one that worked on both a touch screen, and on a normal desktop with a mouse. This is just a very basic example of what is needed to get this feature working on both.

Background

Some time back I had to develop an HTML5 customer input form which also included a signature. This would be used mostly on a tablet, however it was possible it needed to be supported on a drawing pad and a desktop PC. I viewed quite a few online examples of painting on the canvas, but none worked on touch screens AND desktops:
http://mudcu.be/sketchpad/
http://devfiles.myopera.com/articles/649/example5.html

This is simply an alternate to Gordon Kushner's article on the HTML5 canvas & painting. His article can be found here: http://www.codeproject.com/Articles/351253/HTML-5-Canvas-A-Simple-Paint-Program. His code works well; though again it does not work on a touch device.

Most of the code here I found from various examples on Code Project and Stack Overflow. I simply put them all together to get this demo working.

Using the code

This code simply determines which device type you are using and sets up the canvas event handlers accordingly.

HTML

<!DOCTYPE html>
<html lang="en">
<head>
   <meta charset="utf-8" />
   <title>Desktops and Tablets</title>
 
   <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
 
   <script type="text/javascript">
      $(document).ready(function () {
         initialize();
      });
 

      // works out the X, Y position of the click inside the canvas from the X, Y position on the page
      function getPosition(mouseEvent, sigCanvas) {
         var x, y;
         if (mouseEvent.pageX != undefined && mouseEvent.pageY != undefined) {
            x = mouseEvent.pageX;
            y = mouseEvent.pageY;
         } else {
            x = mouseEvent.clientX + document.body.scrollLeft + document.documentElement.scrollLeft;
            y = mouseEvent.clientY + document.body.scrollTop + document.documentElement.scrollTop;
         }
 
         return { X: x - sigCanvas.offsetLeft, Y: y - sigCanvas.offsetTop };
      }
 
      function initialize() {
         // get references to the canvas element as well as the 2D drawing context
         var sigCanvas = document.getElementById("canvasSignature");
         var context = sigCanvas.getContext("2d");
         context.strokeStyle = 'Black';
 
         // This will be defined on a TOUCH device such as iPad or Android, etc.
         var is_touch_device = 'ontouchstart' in document.documentElement;
 
         if (is_touch_device) {
            // create a drawer which tracks touch movements
            var drawer = {
               isDrawing: false,
               touchstart: function (coors) {
                  context.beginPath();
                  context.moveTo(coors.x, coors.y);
                  this.isDrawing = true;
               },
               touchmove: function (coors) {
                  if (this.isDrawing) {
                     context.lineTo(coors.x, coors.y);
                     context.stroke();
                  }
               },
               touchend: function (coors) {
                  if (this.isDrawing) {
                     this.touchmove(coors);
                     this.isDrawing = false;
                  }
               }
            };
 
            // create a function to pass touch events and coordinates to drawer
            function draw(event) {
 
               // get the touch coordinates.  Using the first touch in case of multi-touch
               var coors = {
                  x: event.targetTouches[0].pageX,
                  y: event.targetTouches[0].pageY
               };
 
               // Now we need to get the offset of the canvas location
               var obj = sigCanvas;
 
               if (obj.offsetParent) {
                  // Every time we find a new object, we add its offsetLeft and offsetTop to curleft and curtop.
                  do {
                     coors.x -= obj.offsetLeft;
                     coors.y -= obj.offsetTop;
                  }
				  // The while loop can be "while (obj = obj.offsetParent)" only, which does return null
				  // when null is passed back, but that creates a warning in some editors (i.e. VS2010).
                  while ((obj = obj.offsetParent) != null);
               }
 
               // pass the coordinates to the appropriate handler
               drawer[event.type](coors);
            }
 

            // attach the touchstart, touchmove, touchend event listeners.
            sigCanvas.addEventListener('touchstart', draw, false);
            sigCanvas.addEventListener('touchmove', draw, false);
            sigCanvas.addEventListener('touchend', draw, false);
 
            // prevent elastic scrolling
            sigCanvas.addEventListener('touchmove', function (event) {
               event.preventDefault();
            }, false); 
         }
         else {
 
            // start drawing when the mousedown event fires, and attach handlers to
            // draw a line to wherever the mouse moves to
            $("#canvasSignature").mousedown(function (mouseEvent) {
               var position = getPosition(mouseEvent, sigCanvas);
 
               context.moveTo(position.X, position.Y);
               context.beginPath();
 
               // attach event handlers
               $(this).mousemove(function (mouseEvent) {
                  drawLine(mouseEvent, sigCanvas, context);
               }).mouseup(function (mouseEvent) {
                  finishDrawing(mouseEvent, sigCanvas, context);
               }).mouseout(function (mouseEvent) {
                  finishDrawing(mouseEvent, sigCanvas, context);
               });
            });
 
         }
      }
 
      // draws a line to the x and y coordinates of the mouse event inside
      // the specified element using the specified context
      function drawLine(mouseEvent, sigCanvas, context) {
 
         var position = getPosition(mouseEvent, sigCanvas);
 
         context.lineTo(position.X, position.Y);
         context.stroke();
      }
 
      // draws a line from the last coordiantes in the path to the finishing
      // coordinates and unbind any event handlers which need to be preceded
      // by the mouse down event
      function finishDrawing(mouseEvent, sigCanvas, context) {
         // draw the line to the finishing coordinates
         drawLine(mouseEvent, sigCanvas, context);
 
         context.closePath();
 
         // unbind any events which could draw
         $(sigCanvas).unbind("mousemove")
                     .unbind("mouseup")
                     .unbind("mouseout");
      }
   </script>
   
</head>
 
<body>
   <h1>Canvas test</h1>
 
   <div id="canvasDiv">
      <!-- It's bad practice (to me) to put your CSS here.  I'd recommend the use of a CSS file! -->
      <canvas id="canvasSignature" width="500px" height="500px" style="border:2px solid #000000;"></canvas>
   </div>
</body>
</html>

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)