Titanium Community Questions & Answer Archive

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no touch events in HTML5 canvas drawing in WebView


from pieces of code gathered from this board I've managed to get a small html5 canvas drawing working on the ipad emulator. However, it doesn't work on a real device.

I'm stuck on what to do, since the code works fine in the emulator.
any clues or leads would be appreciated.


the code is the following:

    var newWebview = Titanium.UI.createWebView({
        top: 0,
        left: 0,
        width: "1024",
        height: "auto",
        backgroundColor: 'transparent'


    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, minimum-scale=1, maximum-scale=1, user-scalable=0"/>  
    <meta name="apple-mobile-web-app-capable" content="yes" />
    <title>HTML5 Draft Tool</title>
    <script type="text/javascript" src="js/jquery.js"></script>
    <style type="text/css">
        body {
            font-family: arial, helvetica;
            font-size: 11px;
            margin: 0px;
            padding: 0px;
<body onload="init()">
    <canvas id="canvas" width="1024" height="700"></canvas>

    <script type="text/javascript"> 

    canvas = document.getElementById( 'canvas' );
    var context = canvas.getContext( '2d' );
    context.fillStyle = '#00f';
    context.fillRect( 50, 50, 200, 200 ); // be sure something is drawing into canvas

    function getPage(event){
        //when on mobile safari, the coordinates information is inside the targetTouches object
        if (event.targetTouches) event = event.targetTouches[0];
        if (event.pageX != null && event.pageY != null) return {pageX: event.pageX, pageY: event.pageY};
        var element = (!document.compatMode || document.compatMode == 'CSS1Compat') ? document.documentElement : document.body;
        return {pageX: event.clientX + element.scrollLeft, pageY: event.clientY + element.scrollTop};

    function onMouseMoveOnCanvas( event ) {

        if ( canvas.drawing ) {
            var page = getPage(event);
            var startX = page.pageX;
            var startY = page.pageY;
            if ( canvas.pathBegun == false ) {
                canvas.pathBegun = true;
            } else {
                context.lineTo( startX, startY );

    function onMouseClickOnCanvas( event )
        canvas.drawing = !canvas.drawing;
        if ( canvas.drawing ) // reset the path when starting over
            canvas.pathBegun = false;

    function init(){    
        context.strokeStyle = '#fff';
        context.lineWidth = 5;
        canvas.addEventListener( 'touchmove', onMouseMoveOnCanvas);
        canvas.addEventListener( 'touchstart', onMouseClickOnCanvas);
        canvas.addEventListener( 'touchend', onMouseClickOnCanvas, false );

— asked September 9th 2010 by Pedro Sousa
  • canvas
  • html5
  • ipad
  • touchmove

3 Answers

  • actually, nothing gets run in the init function. I've added an alert but it isn't showing. :|

    — answered September 9th 2010 by Pedro Sousa
  • <canvas id="myCanvas" ontouchstart="touchstartCanvas(event);" ontouchmove="touchmoveCanvas(event);"</canvas>

    function touchstartCanvas(e) {
        X = e.touches[0].clientX;
        Y = e.touches[0].clientY;
    function touchmoveCanvas(e) {
        X = e.touches[0].clientX;
        Y = e.touches[0].clientY;
    — answered October 2nd 2010 by Pankaj Patel
  • I have the same problem also tried the touchMoveCanvas thing but it won't work :S

    somebody else appearantly got this working, but indeed, the init() function never gets loaded for some reason.

    EDIT: when I put an alert('it does work); in the function init() in the html.

    then put it on a ipod touch, it loads the alert but it doesnt let me draw while it does on the simulator.

    so my init does get loaded now what is the problem?

    — answered October 5th 2010 by Patrick van Zadel
    1 Comment
    • Make sure that you are using "touchstartCanvas(e)" and "touchmoveCanvas(e)" and not "touchMoveCanvas" with "M" capital.

      — commented October 31st 2010 by Pankaj Patel
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