防止 Fabric js 对象向外扩展 canvas 边界

Question

我一直试图将对象（在 canvas 上用 fabric js 构建）始终保持在边界内。它已经在移动和旋转它时实现了。我得到了 Move object within canvas boundary limit 的帮助来实现这一目标。但是当我开始缩放对象时，它只是不断超出边界。我不明白必须做些什么才能将它保持在边界内，即使在缩放时也是如此。请帮我提供一个代码来防止这种行为。如果能附上demo就更好了

    <html>
<head>
    <title>Basic usage</title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.3/fabric.min.js"></script>

</head>
<body>
<canvas id="canvas" style= "border: 1px solid black" height= 480 width = 360></canvas>
<script>
 var canvas = new fabric.Canvas('canvas');
  canvas.add(new fabric.Circle({ radius: 30, fill: '#f55', top: 100, left: 100 }));

  canvas.item(0).set({
    borderColor: 'gray',
    cornerColor: 'black',
    cornerSize: 12,
    transparentCorners: true
  });
  canvas.setActiveObject(canvas.item(0));
  canvas.renderAll();


  canvas.on('object:moving', function (e) {
        var obj = e.target;
         // if object is too big ignore
        if(obj.currentHeight > obj.canvas.height || obj.currentWidth > obj.canvas.width){
            return;
        }        
        obj.setCoords();        
        // top-left  corner
        if(obj.getBoundingRect().top < 0 || obj.getBoundingRect().left < 0){
            obj.top = Math.max(obj.top, obj.top-obj.getBoundingRect().top);
            obj.left = Math.max(obj.left, obj.left-obj.getBoundingRect().left);
        }
        // bot-right corner
        if(obj.getBoundingRect().top+obj.getBoundingRect().height  > obj.canvas.height || obj.getBoundingRect().left+obj.getBoundingRect().width  > obj.canvas.width){
            obj.top = Math.min(obj.top, obj.canvas.height-obj.getBoundingRect().height+obj.top-obj.getBoundingRect().top);
            obj.left = Math.min(obj.left, obj.canvas.width-obj.getBoundingRect().width+obj.left-obj.getBoundingRect().left);
        }
});

</script>
</body>
</html>

我的演示附在这里。 : https://jsfiddle.net/3v0cLaLk/

Answer 1

您可以在对象修改监听器上设置并检查对象是否越界。如果是，那就恢复原状。

this.canvas.on('object:modified', function (options: any) {
    let obj = options.target;
    let boundingRect = obj.getBoundingRect(true);
    if (boundingRect.left < 0
        || boundingRect.top < 0
        || boundingRect.left + boundingRect.width > scope.canvas.getWidth()
        || boundingRect.top + boundingRect.height > scope.canvas.getHeight()) {
        obj.top = obj._stateProperties.top;
        obj.left = obj._stateProperties.left;
        obj.angle = obj._stateProperties.angle;
        obj.scaleX = obj._stateProperties.scaleX;
        obj.scaleY = obj._stateProperties.scaleY;
        obj.setCoords();
        obj.saveState();
    }
});

Answer 2

如果要进行实时预防，应使用 object:scaling 事件，因为 object:modified 仅在转换结束时触发。

1) 添加事件处理器到canvas:

this.canvas.on('object:scaling', (e) => this._handleScaling(e));

2) 在handler函数中，获取新旧对象的bounding rect:

_handleScaling(e) {
  var obj = e.target;
  var brOld = obj.getBoundingRect();
  obj.setCoords();
  var brNew = obj.getBoundingRect();

3) 对于每个边框，检查对象是否已缩放超出 canvas 边界并计算其左侧、顶部和缩放属性：

  // left border
  // 1. compute the scale that sets obj.left equal 0
  // 2. compute height if the same scale is applied to Y (we do not allow non-uniform scaling)
  // 3. compute obj.top based on new height
  if(brOld.left >= 0 && brNew.left < 0) {
    let scale = (brOld.width + brOld.left) / obj.width;
    let height = obj.height * scale;
    let top = ((brNew.top - brOld.top) / (brNew.height - brOld.height) *
      (height - brOld.height)) + brOld.top;
    this._setScalingProperties(0, top, scale);
  }

4) 其他边框的类似代码：

  // top border
  if(brOld.top >= 0 && brNew.top < 0) {
    let scale = (brOld.height + brOld.top) / obj.height;
    let width = obj.width * scale;
    let left = ((brNew.left - brOld.left) / (brNew.width - brOld.width) * 
      (width - brOld.width)) + brOld.left;
    this._setScalingProperties(left, 0, scale);
  }
  // right border
  if(brOld.left + brOld.width <= obj.canvas.width 
  && brNew.left + brNew.width > obj.canvas.width) {
    let scale = (obj.canvas.width - brOld.left) / obj.width;
    let height = obj.height * scale;
    let top = ((brNew.top - brOld.top) / (brNew.height - brOld.height) * 
      (height - brOld.height)) + brOld.top;
    this._setScalingProperties(brNew.left, top, scale);
  }
  // bottom border
  if(brOld.top + brOld.height <= obj.canvas.height 
  && brNew.top + brNew.height > obj.canvas.height) {
    let scale = (obj.canvas.height - brOld.top) / obj.height;
    let width = obj.width * scale;
    let left = ((brNew.left - brOld.left) / (brNew.width - brOld.width) * 
      (width - brOld.width)) + brOld.left;
    this._setScalingProperties(left, brNew.top, scale);
  }

5) 如果对象的 BoundingRect 已经越过 canvas 边界，固定它的位置和比例：

  if(brNew.left < 0
  || brNew.top < 0
  || brNew.left + brNew.width > obj.canvas.width
  || brNew.top + brNew.height > obj.canvas.height) {
    obj.left = this.scalingProperties['left'];
    obj.top = this.scalingProperties['top'];
    obj.scaleX = this.scalingProperties['scale'];
    obj.scaleY = this.scalingProperties['scale'];
    obj.setCoords();
  } else {
    this.scalingProperties = null;
  }
}

6) 最后，在设置缩放属性时，我们必须坚持使用最小的比例，以防对象跨越多个边界：

_setScalingProperties(left, top, scale) {
  if(this.scalingProperties == null 
  || this.scalingProperties['scale'] > scale) {
    this.scalingProperties = {
      'left': left,
      'top': top,
      'scale': scale
    };
  }
}

Answer 3

我能够解决问题如下：

var canvas = new fabric.Canvas('canvas');
  canvas.add(new fabric.Circle({ radius: 30, fill: '#f55', top: 100, left: 100 }));

  canvas.item(0).set({
    borderColor: 'gray',
    cornerColor: 'black',
    cornerSize: 12,
    transparentCorners: true
  });
  canvas.setActiveObject(canvas.item(0));
  canvas.renderAll();


  canvas.on('object:moving', function (e) {
        var obj = e.target;
         // if object is too big ignore
        if(obj.currentHeight > obj.canvas.height || obj.currentWidth > obj.canvas.width){
            return;
        }        
        obj.setCoords();        
        // top-left  corner
        if(obj.getBoundingRect().top < 0 || obj.getBoundingRect().left < 0){
            obj.top = Math.max(obj.top, obj.top-obj.getBoundingRect().top);
            obj.left = Math.max(obj.left, obj.left-obj.getBoundingRect().left);
        }
        // bot-right corner
        if(obj.getBoundingRect().top+obj.getBoundingRect().height  > obj.canvas.height || obj.getBoundingRect().left+obj.getBoundingRect().width  > obj.canvas.width){
            obj.top = Math.min(obj.top, obj.canvas.height-obj.getBoundingRect().height+obj.top-obj.getBoundingRect().top);
            obj.left = Math.min(obj.left, obj.canvas.width-obj.getBoundingRect().width+obj.left-obj.getBoundingRect().left);
        }
});

    var left1 = 0;
    var top1 = 0 ;
    var scale1x = 0 ;    
    var scale1y = 0 ;    
    var width1 = 0 ;    
    var height1 = 0 ;
  canvas.on('object:scaling', function (e){
    var obj = e.target;
    obj.setCoords();
    var brNew = obj.getBoundingRect();
    
    if (((brNew.width+brNew.left)>=obj.canvas.width) || ((brNew.height+brNew.top)>=obj.canvas.height) || ((brNew.left<0) || (brNew.top<0))) {
    obj.left = left1;
    obj.top=top1;
    obj.scaleX=scale1x;
    obj.scaleY=scale1y;
    obj.width=width1;
    obj.height=height1;
  }
    else{    
      left1 =obj.left;
      top1 =obj.top;
      scale1x = obj.scaleX;
      scale1y=obj.scaleY;
      width1=obj.width;
      height1=obj.height;
    }
 });

<html>
<head>
    <title>Basic usage</title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.3/fabric.min.js"></script>

</head>
<body>
<canvas id="canvas" style= "border: 1px solid black" height= 480 width = 360></canvas>
</body>
</html>

Answer 4

下面是从各个方向屏蔽canvas区域外任何物体坐标的代码

canvas.on('object:modified', function (data) {
var currentObject = data.target;
var tempObject = angular.copy(data.target);
var canvasMaxWidth = canvas.width - 20,
    canvasMaxHeight = canvas.height - 20;
    var actualWidth = currentObject.getBoundingRect().width,
    actualHeight = currentObject.getBoundingRect().height;
if (actualHeight > canvasMaxHeight) {
    currentObject.scaleToHeight(canvasMaxHeight);
    currentObject.setCoords();
    canvas.renderAll();
    if (tempObject.scaleX < currentObject.scaleX) {
        currentObject.scaleX = tempObject.scaleX;
        currentObject.setCoords();
        canvas.renderAll();
    }
    if (tempObject.scaleY < currentObject.scaleY) {
        currentObject.scaleY = tempObject.scaleY;
        currentObject.setCoords();
        canvas.renderAll();
    }
        if (currentObject.getBoundingRectHeight() < canvasMaxHeight - 50) {
            currentObject.scaleX = (currentObject.scaleX * canvasMaxHeight) / (currentObject.scaleX * currentObject.width);
            currentObject.setCoords();
            canvas.renderAll();
        }

}
if (actualWidth > canvasMaxWidth) {
    currentObject.scaleToWidth(canvasMaxWidth);
    obj.setCoords();
    canvas.renderAll();
    if (tempObject.scaleX < currentObject.scaleX) {
        currentObject.scaleX = tempObject.scaleX;
        currentObject.setCoords();
        canvas.renderAll();
    }
    if (tempObject.scaleY < currentObject.scaleY) {
        currentObject.scaleY = tempObject.scaleY;
        currentObject.setCoords();
        canvas.renderAll();
    }
}
obj.setCoords();
canvas.renderAll();
});

Answer 5

我能够使用最新版本的 Fabric（“fabric”：“^4.6.0”）和 Typescript 按以下方式使用边界框阻止边界外的移动：

private boundingBox: fabric.Rect = null;

this.setBoundingBox(width, height);

private setBoundingBox(width: number, height: number) {
        this.boundingBox = new fabric.Rect({
            name: OBJECT_TYPE.BOUNDING_BOX,
            fill: DEFINITIONS.BG_COLOR,
            width: width,
            height: height,
            hasBorders: false,
            hasControls: false,
            lockMovementX: true,
            lockMovementY: true,
            selectable: false,
            evented: false,
            stroke: 'red',
        });
        this._canvas.add(this.boundingBox);
    }

this._canvas.on('object:moving', (e) => {
            console.log('object:moving');
            this._avoidObjectMovingOutsideOfBoundaries(e);
        });

private _avoidObjectMovingOutsideOfBoundaries(e: IEvent) {
        let obj = e.target;
        const top = obj.top;
        const bottom = top + obj.height;
        const left = obj.left;
        const right = left + obj.width;

        const topBound = this.boundingBox.top;
        const bottomBound = topBound + this.boundingBox.height;
        const leftBound = this.boundingBox.left;
        const rightBound = leftBound + this.boundingBox.width;

        obj.left = Math.min(Math.max(left, leftBound), rightBound - obj.width);
        obj.top = Math.min(Math.max(top, topBound), bottomBound - obj.height);

        return obj;
    }

欢迎对缩放对象进行任何其他扩展。

防止 Fabric js 对象向外扩展 canvas 边界

Prevent Fabric js Objects from scaling out of the canvas boundary

javascript

html5-canvas

fabricjs