html5问题中画布上的事件监听器 [英] event listener on canvas in html5 issue

问题描述

我是html5中的新手，我想在我的鼠标上创建一个事件监听器，我已经编写了以下代码，但是无法理解y，我无法在我的canvas元素上创建事件监听器，请帮助

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);

根据我想要给我的事件监听器代码，可能也有错误

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();
     }

}

推荐答案

您想要将事件添加到画布，而不是2d上下文：

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

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

这是一个演示： jsFiddle链接

Here is a demo: jsFiddle link

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