如何在fabricJS中通过鼠标选择覆盖的对象? [英] How to select covered objects via mouse in fabricJS?

问题描述

我正在尝试开发一种方法来选择位于其他对象下面和(完全)覆盖的对象.一种想法是选择顶部对象，然后通过 doubleclick 向下遍历图层.这是我目前所得到的:

I'm trying to develop a way to select objects that are layered below and (totally) covered by other objects. One idea is to select the top object and then via doubleclick walk downwards through the layers. This is what I got at the moment:

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

fabric.util.addListener(canvas.upperCanvasEl, "dblclick", function (e) {
  var _canvas = canvas;
  var _mouse = _canvas.getPointer(e);
  var _active = _canvas.getActiveObject();
    
  if (e.target) {
    var _targets = _canvas.getObjects().filter(function (_obj) {
      return _obj.containsPoint(_mouse);
    });
      
    //console.warn(_targets);
      
    for (var _i=0, _max=_targets.length; _i<_max; _i+=1) {
      //check if target is currently active
      if (_targets[_i] == _active) {
       	//then select the one on the layer below
       	_targets[_i-1] && _canvas.setActiveObject(_targets[_i-1]);
         break;
        }
      }
    }
});

canvas
  .add(new fabric.Rect({
    top: 25,
    left: 25,
    width: 100,
    height: 100,
    fill: "red"
  }))
  .add(new fabric.Rect({
    top: 50,
    left: 50,
    width: 100,
    height: 100,
    fill: "green"
  }))
  .add(new fabric.Rect({
    top: 75,
    left: 75,
    width: 100,
    height: 100,
    fill: "blue"
  }))
  .renderAll();

canvas {
 border: 1px solid;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.6.3/fabric.min.js"></script>
<canvas id="c" width="300" height="200"></canvas>

如您所见，尝试从 blue 内选择 red 矩形不起作用.我只能选择绿色或蓝色.我猜想在第一个 doubleclick 工作成功之后(选择了 green )，再次单击只是选择了 blue ，因此接下来的双击只能获得<再次>绿色.

As you can see, trying to select the red rectangle from within the blue one is not working. I'm only able to select the green or the blue. I guess that after the first doubleclick worked (green is selected), clicking again just selects blue so the following doubleclick is only able to get green again.

有没有解决的办法?还有其他想法吗?

推荐答案

一段时间后，我终于能够自己解决这个问题.单击一个对象将其带到顶部.双击时，我尝试使该对象位于当前对象的后一层.在另一个dblclick上，我得到了一个，依此类推.对我来说非常有用，并且还可以选择完全覆盖的对象，而无需移动其他对象.

After some time I finally was able to solve that by myself. Clicking on an object brings it to the top. On double-clicking I try to get the object one layer behind the current object. On another dblclick I get the one behind and so on. Works great for me and also allows for the selection of fully covered objects without the need to move others.

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

canvas.on("object:selected", function (e) {
  if (e.target) {
    e.target.bringToFront();
    this.renderAll();
  }
});

var _prevActive = 0;
var _layer = 0;

//
fabric.util.addListener(canvas.upperCanvasEl, "dblclick", function (e) {
    var _canvas = canvas;
    //current mouse position
    var _mouse = _canvas.getPointer(e);
    //active object (that has been selected on click)
    var _active = _canvas.getActiveObject();
    //possible dblclick targets (objects that share mousepointer)
    var _targets = _canvas.getObjects().filter(function (_obj) {
        return _obj.containsPoint(_mouse) && !_canvas.isTargetTransparent(_obj, _mouse.x, _mouse.y);
    });
    
    _canvas.deactivateAll();
      
    //new top layer target
    if (_prevActive !== _active) {
        //try to go one layer below current target
        _layer = Math.max(_targets.length-2, 0);
    }
    //top layer target is same as before
    else {
        //try to go one more layer down
        _layer = --_layer < 0 ? Math.max(_targets.length-2, 0) : _layer;
    }

    //get obj on current layer
    var _obj = _targets[_layer];

    if (_obj) {
    	_prevActive = _obj;
    	_obj.bringToFront();
    	_canvas.setActiveObject(_obj).renderAll();
    }
});

//create something to play with
canvas
  //fully covered rect is selectable with dblclicks
  .add(new fabric.Rect({
    top: 75,
    left: 75,
    width: 50,
    height: 50,
    fill: "black",
    stroke: "black",
    globalCompositeOperation: "xor",
    perPixelTargetFind: true
  }))
  .add(new fabric.Circle({
    top: 25,
    left: 25,
    radius: 50,
    fill: "rgba(255,0,0,.5)",
    stroke: "black",
    perPixelTargetFind: true
  }))
  .add(new fabric.Circle({
    top: 50,
    left: 50,
    radius: 50,
    fill: "rgba(0,255,0,.5)",
    stroke: "black",
    perPixelTargetFind: true
  }))
  .add(new fabric.Circle({
    top: 75,
    left: 75,
    radius: 50,
    fill: "rgba(0,0,255,.5)",
    stroke: "black",
    perPixelTargetFind: true
  }))
  .renderAll();

canvas {
 border: 1px solid;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.6.4/fabric.min.js"></script>
<canvas id="c" width="300" height="200"></canvas>

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