javascript - event listener on canvas in html5 issue - Stack Overflow

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i am new in html5 , i want to create a event listener on my mouse , i have written the following code , but cannot understand y , i cant create the event listener on my canvas element , kindly help

     var canvasDiv = document.getElementById('canvas');
     canvas_simple = document.createElement('canvas');
     canvas_simple.setAttribute('height', canvasHeight);
     canvas_simple.setAttribute('id', 'canvasSimple');
     canvasDiv.appendChild(canvas_simple);
     if(typeof G_vmlCanvasManager != 'undefined')
     {
     canvas_simple = G_vmlCanvasManager.initElement(canvas_simple);
     }
     context_simple = canvas_simple.getContext("2d");
    context_simple.addEventListener('mousemove', ev_mousemove, false);

in light of a ans i want give me event listener code also , may be it has a error also

  var started = false;
  function ev_mousemove (ev) {
  var x, y;

   if (ev.layerX || ev.layerX == 0) { // Firefox
  x = ev.layerX;
  y = ev.layerY;
  } 
  else if (ev.offsetX || ev.offsetX == 0) { // Opera
  x = ev.offsetX;
  y = ev.offsetY;
  }
  if (!started) {

  context.beginPath();
  context.moveTo(x, y);
  started = true;
  }
  else {
    context.strokeStyle = "#df4b26";
    context.lineJoin = "round";
    context.lineWidth = 10;
    context.lineTo(x, y);
    context.stroke();
     }

}

i am new in html5 , i want to create a event listener on my mouse , i have written the following code , but cannot understand y , i cant create the event listener on my canvas element , kindly help

     var canvasDiv = document.getElementById('canvas');
     canvas_simple = document.createElement('canvas');
     canvas_simple.setAttribute('height', canvasHeight);
     canvas_simple.setAttribute('id', 'canvasSimple');
     canvasDiv.appendChild(canvas_simple);
     if(typeof G_vmlCanvasManager != 'undefined')
     {
     canvas_simple = G_vmlCanvasManager.initElement(canvas_simple);
     }
     context_simple = canvas_simple.getContext("2d");
    context_simple.addEventListener('mousemove', ev_mousemove, false);

in light of a ans i want give me event listener code also , may be it has a error also

  var started = false;
  function ev_mousemove (ev) {
  var x, y;

   if (ev.layerX || ev.layerX == 0) { // Firefox
  x = ev.layerX;
  y = ev.layerY;
  } 
  else if (ev.offsetX || ev.offsetX == 0) { // Opera
  x = ev.offsetX;
  y = ev.offsetY;
  }
  if (!started) {

  context.beginPath();
  context.moveTo(x, y);
  started = true;
  }
  else {
    context.strokeStyle = "#df4b26";
    context.lineJoin = "round";
    context.lineWidth = 10;
    context.lineTo(x, y);
    context.stroke();
     }

}

• javascript
• html
• html5-canvas

Share Improve this question Follow edited Sep 7, 2011 at 17:15 Faizan Tanveer asked Sep 7, 2011 at 17:05 Faizan TanveerFaizan Tanveer 33566 silver badges1717 bronze badges

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2 Answers 2

Sorted by: Reset to default 4

You want to add the event to your canvas, not the 2d context:

canvas_simple.addEventListener('mousemove', ev_mousemove, false);

Here is a demo: jsFiddle link

There are a few mistakes:

• You cannot attach the listener to the context, listeners can only be attached to: a single node in a document, the document itself, a window, or an XMLHttpRequest. So you should attach it to the canvas element.

• You cannot nest canvas

• The canvasHeight property is not defined

I created a jsfiddle with your example modified and working --> here

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