javascript - 向前发送多个对象会改变它们的顺序(z-index)

Question

以下代码片段在红色方 block 上方有一个绿色方 block

1. 通过拖动来选择两个方 block 。
2. 点击转发按钮

点击前移后，方 block 的顺序已改变。据我了解，这些项目应该保持相同的顺序，但随着进一步单击按钮，这些项目应该逐渐移动到其他未选定的项目之上。

如果取消选择并重复实验，您将看到它们再次切换。

有什么想法吗？

var canvas = new fabric.Canvas('c', 
{
  preserveObjectStacking	: true
});

var rect = new fabric.Rect({
  left: 10, top: 10,
  fill: 'red',
  width: 100, height: 100,
  hasControls: true
});

canvas.add(rect);

var rect2 = new fabric.Rect({
  left: 40, top: 40,
  fill: 'green',
  width: 100, height: 100,
  hasControls: true
});

canvas.add(rect2);

$("#bringForward").click(function()
{
	var items = canvas.getActiveObject() || canvas.getActiveGroup();

	if(items)
		items.bringForward();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.6/fabric.min.js"></script>
<button id="bringForward">Bring Forward</button>

<canvas id="c" width="640" height="480"></canvas>

Answer 1

这是否可以被视为错误，取决于您期望该函数执行什么操作。

该功能的文档说:在绘制的对象堆栈中向上移动对象或选择内容并且实际上正在这样做。上面的物体不能再往上移动，下面的物体可以移动。

对于开发人员来说，这看起来像是一种奇怪的行为，但对我来说并非如此。但猜测是个人的。

这是您的小部件，其中包含经过修改的代码片段，以尝试更好的解决方案。

var removeFromArray = fabric.util.removeFromArray;

// modified function to avoid snapping
fabric.StaticCanvas.prototype.bringForward = function (object, intersecting) {
      if (!object) {
        return this;
      }
      var activeGroup = this._activeGroup,
          i, obj, idx, newIdx, objs, latestIndex;

      if (object === activeGroup) {
        objs = activeGroup._objects;
        latestIndex = this._objects.length;
        for (i = objs.length; i--;) {
          obj = objs[i];
          idx = this._objects.indexOf(obj);
          if (idx !== this._objects.length - 1 && idx < latestIndex - 1) {
            newIdx = idx + 1;
            latestIndex = newIdx;
            removeFromArray(this._objects, obj);
            this._objects.splice(newIdx, 0, obj);
          } else {
            latestIndex = idx;
          }
        }
      }
      else {
        idx = this._objects.indexOf(object);
        if (idx !== this._objects.length - 1) {
          // if object is not on top of stack (last item in an array)
          newIdx = this._findNewUpperIndex(object, idx, intersecting);
          removeFromArray(this._objects, object);
          this._objects.splice(newIdx, 0, object);
        }
      }
      this.renderAll && this.renderAll();
      return this;
    };


var canvas = new fabric.Canvas('c', 
{
  preserveObjectStacking	: true
});

var rect = new fabric.Rect({
  left: 10, top: 10,
  fill: 'red',
  width: 100, height: 100,
  hasControls: true
});

canvas.add(rect);

var rect2 = new fabric.Rect({
  left: 40, top: 40,
  fill: 'green',
  width: 100, height: 100,
  hasControls: true
});

canvas.add(rect2);

var rect3 = new fabric.Rect({
  left: 70, top: 70,
  fill: 'blue',
  width: 100, height: 100,
  hasControls: true
});

canvas.add(rect3);

var rect4 = new fabric.Rect({
  left: 100, top: 100,
  fill: 'orange',
  width: 100, height: 100,
  hasControls: true
});

canvas.add(rect4);

$("#bringForward").click(function()
{
	var items = canvas.getActiveObject() || canvas.getActiveGroup();

	if(items)
		items.bringForward();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.6/fabric.min.js"></script>
<button id="bringForward">Bring Forward</button>

<canvas id="c" width="640" height="480"></canvas>