鼠标单击时在多个对象上选择 Fabricjs

Question

关于在画布鼠标单击上选择多个对象有什么建议吗？不是所有对象，我想选择覆盖在该点上的对象。

据我所知，鼠标事件的目标始终只是最顶层的对象。 我曾尝试在对象上绑定事件，但它不会为背面的那些触发。 我曾尝试根据项目大小和高度进行选择，但旋转后无法正常工作。

var canvas = this.__canvas = new fabric.Canvas('c', {
  enableRetinaScaling: false
});

function LoopOnObjects(e) {
  var mouse = canvas.getPointer(e.e, false);
  var x = Math.ceil(mouse.x);
  var y = Math.ceil(mouse.y);

  var count = 0;
  canvas.getObjects().forEach(function(object, index){
    if(CheckObjectWithin(object, x, y)) {
        count++;
    }
  });

  alert("ya, there is " + count + " objects touch on click");
}

function CheckObjectWithin(object, x, y) {
    var objectBoundRect = object.getBoundingRect(true);
    var widthRange = objectBoundRect.width;
    var heightRange = objectBoundRect.height;

    if (x > objectBoundRect.left && x < objectBoundRect.left + widthRange) {
        if (y > objectBoundRect.top && y < objectBoundRect.top + heightRange) {
            return true;
        }
    }

    return false;
}

function GetElement(e) {
    LoopOnObjects(e);
}

canvas.on("mouse:up", GetElement);

canvas.add(new fabric.Rect({
    width: 100, height: 100, left: 100, top: 20, angle: -10,
    fill: 'rgba(0,200,0,0.5)'
  }));
canvas.add(new fabric.Rect({
    width: 50, height: 100, left: 220, top: 80, angle: 45,
    stroke: '#eee', strokeWidth: 10,
    fill: 'rgba(0,0,200,0.5)'
  }));
canvas.add(new fabric.Circle({
    radius: 50, left: 220, top: 175, fill: '#aac'
  }));

template for testing

Answer 1

实际上，已经有一个库方法：fabric.Object.prototype.containsPoint()。它适用于旋转，但请记住，该点是根据边界框而不是可见形状检查的（例如，圆形仍然有一个矩形边界框）。

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

function loopOnObjects(e) {
  var mouse = canvas.getPointer(e.e, false);
  var point = new fabric.Point(mouse.x, mouse.y)
  
  var count = 0;
  canvas.getObjects().forEach(function(object, index){
    if (object.containsPoint(point)) {
    	count++;
    }
  });
}

function getElement(e) {
	loopOnObjects(e);
}

canvas.on("mouse:down", getElement);

canvas.add(new fabric.Rect({
    width: 100, height: 100, left: 100, top: 20, angle: -10,
    fill: 'rgba(0,200,0,0.5)'
  }));
canvas.add(new fabric.Rect({
    width: 50, height: 100, left: 220, top: 80, angle: 45,
    stroke: '#eee', strokeWidth: 10,
    fill: 'rgba(0,0,200,0.5)'
  }));
canvas.add(new fabric.Circle({
    radius: 50, left: 220, top: 175, fill: '#aac'
  }));

#c {
    border: 1px black solid;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.22/fabric.min.js"></script>
<canvas id="c" width="500" height="300"></canvas>