fabricjs，旋转对象后，可以得到左右矩形的位置

Question

旋转对象后，能否获得虚拟矩形的左，上，右位置？

Answer 1

您要寻找的是对象的边界矩形：

getBoundingRect（ignoreVpt）？{Object}返回框要与画布的轴对齐的对象边界矩形（左，上，宽，高）的坐标。

返回：具有left，top，width，height属性的对象类型Object

参考：fabricjs源代码

var canvas = this.__canvas = new fabric.Canvas('c');
fabric.Object.prototype.transparentCorners = false;
var rect = new fabric.Rect({
  left: 120,
  top: 30,
  width: 100,
  height: 100,
  fill: 'green',
  angle: 20
});

canvas.on('after:render', function() {
  canvas.contextContainer.strokeStyle = '#555';
  canvas.forEachObject(function(obj) {
    var bound = obj.getBoundingRect(); // <== this is the magic
    console.log(bound);
    canvas.contextContainer.strokeRect(
      bound.left,
      bound.top,
      bound.width,
      bound.height
    );

  });

});
canvas.add(rect);

<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.js"></script>
<canvas height=200 width=300 id="c" style="border:1px solid black"></canvas>

由于在after:render渲染每一帧后都会连续触发该事件，因此您可以看到对象的每次更新（位置，旋转和尺寸）的更新边界框。

var canvas = this.__canvas = new fabric.Canvas('c');
fabric.Object.prototype.transparentCorners = false;
var rect = new fabric.Rect({
  left: 120,
  top: 30,
  width: 100,
  height: 100,
  fill: 'green',
  angle: 20
});
canvas.add(rect);
canvas.on('after:render', function() {
  canvas.contextContainer.strokeStyle = '#555';
  var ao = canvas.getActiveObject();
  if (ao) {
    var bound = ao.getBoundingRect();

    canvas.contextContainer.strokeRect(
      bound.left,
      bound.top,
      bound.width,
      bound.height
    );
    console.log(bound);

  }
});

<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.js"></script>
<canvas height=200 width=300 id="c" style="border:1px solid black"></canvas>

供参考使用事件