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Asked: 2026-05-19T23:32:01+00:00

I’m studying jquery and html5 canvas. All I want to do is a simple

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I’m studying jquery and html5 canvas. All I want to do is a simple html5 drawing example. When the mouse move, I draw red squares under my mouse.

My code is simple, but I have a problem getting the mouse cursor position within the canvas.

Right now, I am using x=event.offsetX; to get the mouse position. This works very well in chrome, however when it comes to firefox, it doesn’t work. I changed the code to x=event.layerX. but it seems that layerX is the position of my mouse relative to the web page, not the position of the canvas. because I always see an offset.

I have two questions, first, what is the right thing to do to get the correct mouse position under firefox. second, how can i write a code that works for ie, firefox, chrome, safari and opera?

here is my code:

 <!doctype html />
<html><head>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript">
  $(document).ready(
 function(){

var flip = document.getElementById('flip');
    var context = flip.getContext('2d');   
context.fillStyle = "rgb(255,255,255)";   
context.fillRect(0, 0, 500, 500);

      $("a").click(function(event){alert("Thanks for visiting!");});
   $("#flip").mousemove(function(event){
      var x, y;


    x = event.layerX;
    y = event.layerY;


    //alert("mouse pos"+event.layerX );
    var flip = document.getElementById('flip');
    var context = flip.getContext('2d');   
context.fillStyle = "rgb(255,0,0)";   
context.fillRect(x, y, 5, 5);
    }
   );
  }
  );    
  </script>
  </head>  <body bgcolor="#000000"> <a href="http://jquery.com/">jQuery</a><canvas id="flip" width="500" height="500">
  This text is displayed if your browser does not support HTML5 Canvas.</canvas> </body></html>
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1 Answer

  1. Editorial Team

    enter image description here

    <!DOCTYPE html>

<html>
    <head>
        <meta charset = "utf-8">

        <script>
            Element.prototype.leftTopScreen = function () {
                var x = this.offsetLeft;
                var y = this.offsetTop;

                var element = this.offsetParent;

                while (element !== null) {
                    x = parseInt (x) + parseInt (element.offsetLeft);
                    y = parseInt (y) + parseInt (element.offsetTop);

                    element = element.offsetParent;
                }

                return new Array (x, y);
            }

            document.addEventListener ("DOMContentLoaded", function () {
                var flip = document.getElementById ("flip");

                var xy = flip.leftTopScreen ();

                var context = flip.getContext ("2d");

                context.fillStyle = "rgb(255,255,255)";   
                context.fillRect (0, 0, 500, 500);

                flip.addEventListener ("mousemove", function (event) {
                    var x = event.clientX;
                    var y = event.clientY;

                    context.fillStyle = "rgb(255, 0, 0)";  
                    context.fillRect (x - xy[0], y - xy[1], 5, 5);
                });
            });    
        </script>

        <style>
            #flip {
                border: 1px solid black;
                display: inline-block;

            }

            body {
                text-align: center;
            }
        </style>
    </head>

    <body>
        <canvas id = "flip" width = "500" height = "500">This text is displayed if your browser does not support HTML5 Canvas.</canvas>
    </body>
</html>

    You don’t have to worry about compatibility, only IE (prior 9) does not support canvas natively.

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