7

我在设置画布相对于另一个画布的位置时遇到问题，因此我编写了以下测试工具。

我希望线束顶部 div 中“top”和“left”指定的位置会相对于彼此移动画布的原点。

我究竟做错了什么？

<!DOCTYPE html>
<html>
<head>
<form id='form1' style="position:relative">
  <div id='d1' style="position:absolute; top:0; left:0; z-index:1">  
      <canvas id='canvas1' width='200' height='100'>
            Your browser does not support HTML5 Canvas.
      </canvas>
  </div>
  <div id='d2' style="position:absolute; top:50; left:50; z-index:2">
      <canvas id='canvas2' width='100' height='200'>
            Your browser does not support HTML5 Canvas.
      </canvas>
  </div>
  <div id='d3' style="position:absolute; top:75; left:75; z-index:3">
      <canvas id='canvas3' width='50' height='50'>
            Your browser does not support HTML5 Canvas.
      </canvas>
  </div>
</form>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<input id='btn1' type="button" onClick="demoDisplay()" value="Hide canvas with display property">
<input id='btn2' type="button" onClick="demoVisibility()" value="Hide canvas with visibility property">
<input id='btn3' type="button" onClick="demoOrder()" value="Place blue over red">

</head>
<body onLoad="loadMe()">


<script>
function loadMe()
{
    var canvas = document.getElementById("canvas1");
    if (canvas.getContext) { // Canvas Support
       var ctx = canvas.getContext("2d");
       // Work with context
       var grd=ctx.createLinearGradient(0,0,ctx.canvas.height,ctx.canvas.width);
       grd.addColorStop(0,'#8ed6ff');
       grd.addColorStop(1,'#004cb3');
       ctx.fillStyle=grd;
       ctx.rect(0,0,ctx.canvas.width,ctx.canvas.height);
       ctx.fill();
    }   
    var canvas = document.getElementById("canvas2");
    if (canvas.getContext) { // Canvas Support
       var ctx = canvas.getContext("2d");
       // Work with context
       var grd=ctx.createLinearGradient(0,0,ctx.canvas.height,ctx.canvas.width);
       grd.addColorStop(0,'#C00');
       grd.addColorStop(1,'#D00');
       ctx.fillStyle=grd;
       ctx.rect(0,0,ctx.canvas.width,ctx.canvas.height);
       ctx.fill();
    }   
    var canvas = document.getElementById("canvas3");
    if (canvas.getContext) { // Canvas Support
       var ctx = canvas.getContext("2d");
       // Work with context
       var grd=ctx.createLinearGradient(0,0,ctx.canvas.height,ctx.canvas.width);
       grd.addColorStop(0,'#00C');
       grd.addColorStop(1,'#00D');
       ctx.fillStyle=grd;
       ctx.rect(0,0,ctx.canvas.width,ctx.canvas.height);
       ctx.fill();
    }   
}

function demoVisibility()
{
    btn = document.getElementById('btn2')
    if (btn.value==='Hide canvas with visibility property') {
        btn.value = 'Show canvas with visibility property';
        document.getElementById("d2").style.visibility="hidden";
    } else {
        btn.value = 'Hide canvas with visibility property';
        document.getElementById("d2").style.visibility="visible";
    }
}

function demoDisplay()
{
    btn = document.getElementById('btn1')
    if (btn.value==='Hide canvas with display property') {
        btn.value = 'Show canvas with display property';
        document.getElementById("d1").style.display="none";
    } else {
        btn.value = 'Hide canvas with display property';
        document.getElementById("d1").style.display="inline";
    }
}

function demoOrder()
{
    btn = document.getElementById('btn3')
    if (btn.value==='Place blue over red') {
        btn.value = 'Place red over blue';
        document.getElementById("d1").style.zIndex=2;
        document.getElementById("d2").style.zIndex=1;
    } else {
        btn.value = 'Place blue over red';
        document.getElementById("d1").style.zIndex=1;
        document.getElementById("d2").style.zIndex=2;
    }
}
</script>

</body>
</html>
4

3 回答 3

13

将“ px ”添加到您的样式测量中。EG top:50;=>top:50px;

<form id='form1' style="position:relative">
    <div id='d1' style="position:absolute; top:0px; left:0px; z-index:1">  
        <canvas id='canvas1' width='200' height='100'>
              Your browser does not support HTML5 Canvas.
        </canvas>
    </div>
    <div id='d2' style="position:absolute; top:50px; left:50px; z-index:2">
        <canvas id='canvas2' width='100' height='200'>
              Your browser does not support HTML5 Canvas.
        </canvas>
    </div>
    <div id='d3' style="position:absolute; top:75px; left:75px; z-index:3">
        <canvas id='canvas3' width='50' height='50'>
              Your browser does not support HTML5 Canvas.
        </canvas>
    </div>
  </form>
于 2013-06-23T22:29:18.763 回答
2

我会让你的生活变得简单。这是相同的javascript代码。

var can = document.querySelector('canvas');
  can.style.position = 'absolute';
  can.style.top = "100px";
  can.style.left = "100px";

好吧，享受页面样式....

于 2020-03-30T08:01:50.790 回答
-3

首先，您的 HTML 无效。内容（HTML 元素，如<form>等<canvas>）应该在<body>标签内的 <html>标签中！<script>应该在<head>.

另外，请注意，解决方案是在使用相对定位的元素内使用绝对定位。

于 2015-07-23T13:47:21.487 回答