troubleshooting Question

Canvas script works in Firefox and IE but not Chrome

Avatar of thenelson
thenelson asked on
Web Graphics SoftwareJavaScriptHTML
17 Comments1 Solution1371 ViewsLast Modified:
The following canvas script works in Firefox and IE but not Chrome. In Chrome, no lines are drawn.  Any ideas why it doesn't work in Chrome?
/* © 2009 ROBO Design
 * http://www.robodesign.ro
 */

// Keep everything in anonymous function, called on window load.
if(window.addEventListener) {
window.addEventListener('load', function () {
  var canvas, context, tool;

  function init () {
    // Find the canvas element.
    canvas = document.getElementById('imageView');
    if (!canvas) {
      alert('Error: I cannot find the canvas element!');
      return;
    }

    if (!canvas.getContext) {
      alert('Error: no canvas.getContext!');
      return;
    }

    // Get the 2D canvas context.
    context = canvas.getContext('2d');
    if (!context) {
      alert('Error: failed to getContext!');
      return;
    }
	
	var img=new Image();
	img.onload = function(){
	context.drawImage(img,0,0);
	};
	img.src="PainDiagram.png";
	
    // Pencil tool instance.
    tool = new tool_pencil();

    // Attach the mousedown, mousemove and mouseup event listeners.
    canvas.addEventListener('mousedown', ev_canvas, false);
    canvas.addEventListener('mousemove', ev_canvas, false);
    canvas.addEventListener('mouseup',   ev_canvas, false);
  }

  // This painting tool works like a drawing pencil which tracks the mouse 
  // movements.
  function tool_pencil () {
    var tool = this;
    this.started = false;

    // This is called when you start holding down the mouse button.
    // This starts the pencil drawing.
    this.mousedown = function (ev) {
		context.beginPath();
		context.lineWidth = 5;
		context.lineCap = "round";
		context.globalAlpha=0.01;
		context.shadowColor="red";
		context.shadowBlur=10;
		context.strokeStyle = "red"; // line color
        context.moveTo(ev._x, ev._y);
        tool.started = true;
    };

    // This function is called every time you move the mouse. Obviously, it only 
    // draws if the tool.started state is set to true (when you are holding down 
    // the mouse button).
    this.mousemove = function (ev) {
      if (tool.started) {
	    //var p = context.getImageData(ev._x, ev._y, 1, 1).data; 
        //if(p[0]==255 && p[1]==204 && p[2]==153){
	        context.moveTo(ev._x, ev._y);
	        context.lineTo(ev._x, ev._y);
	        context.stroke();
		//}
      }
    };

    // This is called when you release the mouse button.
    this.mouseup = function (ev) {
      if (tool.started) {
        tool.mousemove(ev);
        tool.started = false;
      }
    };
  }

  // The general-purpose event handler. This function just determines the mouse 
  // position relative to the canvas element.
  function ev_canvas (ev) {
    if (ev.layerX || ev.layerX == 0) { // Firefox
      ev._x = ev.layerX;
      ev._y = ev.layerY;
    } else if (ev.offsetX || ev.offsetX == 0) { // Opera
      ev._x = ev.offsetX;
      ev._y = ev.offsetY;
    }

    // Call the event handler of the tool.
    var func = tool[ev.type];
    if (func) {
      func(ev);
    }
  }

  init();

}, false); }

// vim:set spell spl=en fo=wan1croql tw=80 ts=2 sw=2 sts=2 sta et ai cin fenc=utf-8 ff=unix:
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Paint</title>
    <style type="text/css"><!--
      #container { position: relative; }
      #imageView { border: 1px solid #000; }
    --></style>
  </head>
  <body BGCOLOR="#CCFFFF"> 
  
    <div id="container">
      <canvas id="imageView" width="700" height="643" margin: 0 auto>
        <p>Unfortunately, your browser is currently unsupported by our web 
        application.  We are sorry for the inconvenience. Please use one of the 
        supported browsers listed below, or draw the image you want using an 
        offline tool.</p>
        <p>Supported browsers: <a href="http://www.opera.com">Opera</a>, <a 
          href="http://www.mozilla.com">Firefox</a>, <a 
          href="http://www.apple.com/safari">Safari</a>, and <a 
          href="http://www.konqueror.org">Konqueror</a>.</p>
      </canvas>
    </div>

    <script type="text/javascript" 
    src="example1.js"></script>
  </body>
</html>
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