javascript-使用fabricjs在画布上添加“出血区域”？

我正在使用fabricjs(1.7.20),并希望创建一种“出血区域”,在该区域中用户无法使用画布周围的一些空间；如果您愿意,可以使用一种“墙”来阻止对象移动到画布墙的侧面.我该怎么做？

var canvas = new fabric.Canvas("c");
canvas.setHeight(350);
canvas.setWidth(350);

canvas.add(new fabric.IText("Some text", {
  top: 25,
}));

var circle = new fabric.Circle({
  radius: 20, fill: 'green', left: 100, top: 100
});
var triangle = new fabric.Triangle({
  width: 20, height: 30, fill: 'blue', left: 150, top: 150
});

canvas.add(circle, triangle);

canvas {
  border: 1px solid #dddddd;
  margin-top: 10px;
  border-radius: 3px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.20/fabric.min.js"></script>
<canvas id="c"></canvas>

这是向我建议的,这是我最近得到的.我正在寻找这样做,但是距画布的边界为10px.

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);
        }
});

解决方法:

您可以通过以下方式添加一个10像素的出血区域：在确定对象是否从“出血”区域移出的条件下加上/减去10(我实际上更喜欢称其为“填充”),然后添加/从计算中减去将对象重新定位在填充边界内的位置.

这是一个有效的更新示例：

var padding = 10;
var canvas = new fabric.Canvas("c");

canvas.setHeight(350);
canvas.setWidth(350);

canvas.add(new fabric.IText("Some text", {
    top: 25,
}));

var circle = new fabric.Circle({
    radius: 20,
    fill: 'green',
    left: 100,
    top: 100
});
var triangle = new fabric.Triangle({
    width: 20,
    height: 30,
    fill: 'blue',
    left: 150,
    top: 150
});

canvas.add(circle, triangle);

canvas.on('object:moving', function(e) {
    var obj = e.target;
    
    // if object is too big ignore
    if (obj.currentHeight > obj.canvas.height - padding * 2 ||
        obj.currentWidth > obj.canvas.width - padding * 2) {
        return;
    }
    obj.setCoords();

    // top-left corner
    if (obj.getBoundingRect().top < padding ||
    	obj.getBoundingRect().left < padding) {
        obj.top = Math.max(obj.top, obj.top - obj.getBoundingRect().top + padding);
        obj.left = Math.max(obj.left, obj.left - obj.getBoundingRect().left + padding);
    }
    
    // bot-right corner
    if (obj.getBoundingRect().top + obj.getBoundingRect().height > obj.canvas.height - padding || 
    	obj.getBoundingRect().left + obj.getBoundingRect().width > obj.canvas.width - padding) {
        obj.top = Math.min(
        	obj.top,
        	obj.canvas.height - obj.getBoundingRect().height + obj.top - obj.getBoundingRect().top - padding);
        obj.left = Math.min(
        	obj.left,
            obj.canvas.width - obj.getBoundingRect().width + obj.left - obj.getBoundingRect().left - padding);
    }
});

canvas {
  border: 1px solid #dddddd;
  margin-top: 10px;
  border-radius: 3px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.20/fabric.min.js"></script>
<canvas id="c"></canvas>

在第一行中,我定义了一个变量“ padding”,它表示所需的填充大小.这样,如果您以后想要更改填充,则不必在八个不同的位置进行更改.

左上角条件中使用的padding变量代替0.

如果“左上”条件为true,则将填充添加到计算中以重新放置对象.

在“右下方”部分,我们做的是相反的–我们从条件中减去填充并从重新定位计算中减去.

您也可以尝试以下小提琴中的代码：https://jsfiddle.net/pahund/hz7jLnme/

标签：canvas,fabricjs,javascript
来源： https://codeday.me/bug/20191110/2014192.html