Fabric Js：如何以编程方式创建矩形，只有左上角和右下角两个点？

Question

可以像这样使用顶部、左侧、宽度、高度来创建矩形

var rect = new fabric.Rect({
   left: 50,
   top: 50,
   width: 50,
   height: 50,
   fill: 'rgba(255,127,39,1)',
});

是否可以通过设置它的 aCoords 左上角和右下角来创建一个矩形？有没有办法只用这两个点创建矩形？

Answer 1

对于你的矩形，

width = difference between top-left x and right-bottom x,
height = difference between top-left y and right-bottom y.

演示

var canvas = new fabric.Canvas('c');

function getValue(id) {
  return document.getElementById(id).value
}

function r() {
  return Math.floor(Math.random() * 255)
}

function getColor() {
  return 'rgb(' + r() + "," + r() + "," + r() + ')';
}

function addRect() {
  var tlx = getValue('tlx'),
    tly = getValue('tly'),
    brx = getValue('brx'),
    bry = getValue('bry');
  if (tlx == '' || tly == '' || brx == '' || bry == '') {
    alert('Enter all values');
    return false;
  }
  var width = Math.abs(+tlx - +brx),
    height = Math.abs(+tly - +bry);

  var rect = new fabric.Rect({
    left: +tlx,
    top: +tly,
    width: width,
    height: height,
    fill: getColor()
  });
  canvas.add(rect);
}

canvas{
 border: 1px solid #000;
}

<script src="https://rawgit.com/kangax/fabric.js/master/dist/fabric.js"></script>
Top-left x: <input type='number' min="0" max="300" id='tlx'><br>
Top-left y: <input type='number' min="0" max="300" id='tly'><br>
Bottom-Right x: <input type='number' min="0" max="300" id='brx'><br>
Bottom-Right x: <input type='number' min="0" max="300"id='bry'><br>
<button onclick='addRect()'>Add</button>
<canvas id="c" width="400" height="300"></canvas>