javascript - 如何自动更新复制的 fabricjs Canvas ？

Question

我有一个 Canvas ，它会在用户按下按钮后 self 复制。我现在很好奇如何才能使它自动化，这样用户就不需要按任何东西；只需更改第一个 Canvas 即可看到更改在进行更改后会自动传播到其他 Canvas 吗？

var canvas = [];
canvas.push(new fabric.Canvas('c0'));
for (i = 1; i <= 7; i++) {
  canvas.push(new fabric.StaticCanvas('sc' + i));
}

var rect = new fabric.Rect({
  fill: '#F5F5F5',
  width: 187.5,
  height: 318.75
});

canvas[0].add(rect);

$('#update').click(function() {
  var json = JSON.stringify(canvas[0]);
  for (i = 1; i <= 7; i++) {
    canvas[i].loadFromJSON(json);
  }
});

$('#save').click(function() {
  html2canvas($('#imagesave'), {
    onrendered: function(canvas) {
      var a = document.createElement('a');
      // toDataURL defaults to png, so we need to request a jpeg, then convert for file download.
      a.href = canvas.toDataURL("image/jpeg").replace("image/jpeg", "image/octet-stream");
      a.download = 'myfile.jpg';
      a.click();
    }
  });
});

body {
  margin: 0px;
  padding: 0px;
}

canvas {
  border: 0px solid #f00;
  margin: 0px;
  display: block;
}

td {
  margin: 0;
  padding: 0;
  border: 0;
  outline: 0;
  vertical-align: baseline;
}

#imagesave {
  background-color: white;
  height: 637.5px;
  width: 825px;
  padding-left: 75px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.22/fabric.min.js"></script>
<button id="update">Update Preview</button>
<button id="save">Save</button>


<div id="imagesave">

  <table>
    <tr>
      <td>
        <canvas id="c0" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc1" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc2" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc3" width="187.5" height="318.75"></canvas>
      </td>
    </tr>
    <tr>
      <td>
        <canvas id="sc4" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc5" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc6" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc7" width="187.5" height="318.75"></canvas>
      </td>
    </tr>
  </table>

</div>

Answer 1

canvas[0].on('object:added', onModified);
canvas[0].on('object:modified', onModified);
canvas[0].on('object:scaling', onModified);
canvas[0].on('object:moving', onModified);

您可以使用此事件并获取修改后的对象(如果存在则将其删除)，然后将其添加到其他 Canvas 。

演示

var canvas = [];
canvas.push(new fabric.Canvas('c0'));
for (i = 1; i <= 7; i++) {
  canvas.push(new fabric.StaticCanvas('sc' + i));
}

var rect = new fabric.Rect({
  fill: '#ff0000',
  width: 100,
  height: 100,
  id : 1
});
var circle = new fabric.Circle({
  fill: '#ffff00',
  radius: 50,
  left: 150,
  top:150,
  originX:'center',
  originY:'center',
  id : 2
});

canvas[0].on('object:added', onModified);
canvas[0].on('object:modified', onModified);
canvas[0].on('object:scaling', onModified);
canvas[0].on('object:moving', onModified);
canvas[0].add(rect,circle);

function onModified(option){
  var ob = option.target;
  var index = canvas[0].getObjects().indexOf(ob);
  ob.clone(function(obj){
    for (i = 1; i <= 7; i++) {
      canvas[i].insertAt(obj, index, true);
    }
  });
};

$('#update').click(function() {
  var json = JSON.stringify(canvas[0]);
  for (i = 1; i <= 7; i++) {
    canvas[i].loadFromJSON(json);
  }
});

$('#save').click(function() {
  html2canvas($('#imagesave'), {
    onrendered: function(canvas) {
      var a = document.createElement('a');
      // toDataURL defaults to png, so we need to request a jpeg, then convert for file download.
      a.href = canvas.toDataURL("image/jpeg").replace("image/jpeg", "image/octet-stream");
      a.download = 'myfile.jpg';
      a.click();
    }
  });
});

body {
  margin: 0px;
  padding: 0px;
}

canvas {
  border: 1px solid #f00;
  margin: 0px;
  display: block;
}

td {
  margin: 0;
  padding: 0;
  border: 0;
  outline: 0;
  vertical-align: baseline;
}

#imagesave {
  background-color: white;
  height: 637.5px;
  width: 825px;
  padding-left: 75px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.22/fabric.js"></script>
<button id="update">Update Preview</button>
<button id="save">Save</button>


<div id="imagesave">

  <table>
    <tr>
      <td>
        <canvas id="c0" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc1" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc2" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc3" width="187.5" height="318.75"></canvas>
      </td>
    </tr>
    <tr>
      <td>
        <canvas id="sc4" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc5" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc6" width="187.5" height="318.75"></canvas>
      </td>
      <td>
        <canvas id="sc7" width="187.5" height="318.75"></canvas>
      </td>
    </tr>
  </table>

</div>