使用fabric.js在画布中加载JSON

Question

我试图用JSON保存数据并使用fabric.js将其加载到画布中。我使用以下简单代码不断收到错误：

canvas.add(new fabric.Rect({ width: 50, height: 50, fill: 'red', top: 100, left: 100 }));
var c = canvas.toJSON();
canvas.clear();
canvas.loadFromJSON(c);

我明白了：

SyntaxError: JSON.parse: unexpected character
[Break On This Error] var Cufon=(function(){var k=function()....Image.fromElement.async=true})(this);

当我使用自己的JSON时，它验证得很好，但是当我使用fabric的方法canvas.toJSON（）输出的任何内容时，我仍然会出错。 任何人都有工作的例子，加载回从fabric.js中先前画布状态保存的空画布数据？ 这将不胜感激！

Answer 1

fabric.Canvas#toJSON实际上返回一个对象，而不是JSON字符串。

对不起，如果这令人困惑。

之所以这样，是因为JSON.stringify 。 关于JSON.stringify的事情是它支持自定义序列化; 您需要做的就是传递一个具有toJSON方法的对象。 这正是我在fabric中所做的 - fabric.Canvas有toJSON方法，它本质上是toObject方法的别名。

这允许我们通过做一些简单的操作来序列化画布：

JSON.stringify(canvas);

..其中canvas是对fabric.Canvas实例的引用。

之间的差toObject和toDatalessObject （以及toJSON和toDatalessJSON ）是toDatalessObject返回“URL”，而不是实际的路径数据。 这样做是为了节省具有大尺寸形状的画布表示的大小。 如果加载大型SVG形状，其路径数据可能会导致数百万字符串。 如果您以后需要序列化此数据（例如，为了保存目的），使用svg形状的URL替换路径数据会更有意义。 想象一下，必须来回上传/下载如此庞大的字符串到服务器。

所以，而不是这个：

{ "angle" : 3,
  "fill" : "#00274D",
  "flipX" : false,
  "flipY" : false,
  "height" : 115,
  "left" : 353,
  "opacity" : 1,
  "overlayFill" : null,
  "path" : [ [ "M",
        67.390000000000001,
        22.390000000000001
      ],
      [ "c",
        2.5899999999999999,
        -0.42999999999999999,
        5.1100000000000003,
        1.4399999999999999,
        5.54,
        4.1799999999999997
      ],
      [ "c",
        0.42999999999999999,
        2.6600000000000001,
        -1.3,
        5.2599999999999998,
        -3.8900000000000001,
        5.6900000000000004
      ],
      [ "c",
        -1.8,
        0.28999999999999998,
        -3.6000000000000001,
        -0.57999999999999996,
        -4.6100000000000003,
        -2.02
      ],
      [ "L",
        44.5,
        34.560000000000002
      ],
      [ "l",
        10.869999999999999,
        59.619999999999997
      ],
      [ "c",
        17.420000000000002,
        -4.46,
        26.059999999999999,
        -14.18,
        27.5,
        -29.02
      ],
      [ "l",
        -10.01,
        -0.71999999999999997
      ],
      [ "L",
        88.700000000000003,
        51.909999999999997
      ],
      [ "l",
        9.4299999999999997,
        21.239999999999998
      ],
      [ "c",
        -3.3799999999999999,
        -1.95,
        -5.9000000000000004,
        -5.1100000000000003,
        -9.2899999999999991,
        -7.0599999999999996
      ],
      [ "c",
        -0.28999999999999998,
        25.059999999999999,
        -27.140000000000001,
        32.759999999999998,
        -33.770000000000003,
        47.950000000000003
      ],
      [ "C",
        44.420000000000002,
        100.08,
        26.5,
        114.77,
        6.9100000000000001,
        82.799999999999997
      ],
      [ "L",
        0,
        92.450000000000003
      ],
      [ "l",
        1.51,
        -21.600000000000001
      ],
      [ "l",
        19.66,
        4.6799999999999997
      ],
      [ "l",
        -9.4299999999999997,
        3.6699999999999999
      ],
      [ "c",
        7.4900000000000002,
        11.59,
        17.57,
        19.870000000000001,
        36.43,
        16.420000000000002
      ],
      [ "L",
        36.219999999999999,
        36.57
      ],
      [ "l",
        -18.649999999999999,
        2.3799999999999999
      ],
      [ "c",
        -0.14000000000000001,
        2.1600000000000001,
        -1.73,
        4.0300000000000002,
        -3.8900000000000001,
        4.3899999999999997
      ],
      [ "c",
        -2.5899999999999999,
        0.42999999999999999,
        -5.04,
        -1.4399999999999999,
        -5.54,
        -4.0999999999999996
      ],
      [ "c",
        -0.42999999999999999,
        -2.7400000000000002,
        1.3,
        -5.2599999999999998,
        3.8900000000000001,
        -5.6900000000000004
      ],
      [ "c",
        1.9399999999999999,
        -0.35999999999999999,
        3.8900000000000001,
        0.65000000000000002,
        4.9000000000000004,
        2.2999999999999998
      ],
      [ "l",
        17.93,
        -4.8200000000000003
      ],
      [ "l",
        -1.3700000000000001,
        -6.8399999999999999
      ],
      [ "c",
        -4.8200000000000003,
        -0.79000000000000004,
        -8.9299999999999997,
        -4.75,
        -9.7899999999999991,
        -10.08
      ],
      [ "c",
        -1.1499999999999999,
        -6.6200000000000001,
        3.1000000000000001,
        -12.890000000000001,
        9.4299999999999997,
        -13.970000000000001
      ],
      [ "c",
        6.4100000000000001,
        -1.01,
        12.460000000000001,
        3.46,
        13.539999999999999,
        10.08
      ],
      [ "c",
        0.85999999999999999,
        5.1799999999999997,
        -1.5800000000000001,
        10.15,
        -5.6900000000000004,
        12.6
      ],
      [ "l",
        1.8700000000000001,
        6.1200000000000001
      ],
      [ "l",
        20.739999999999998,
        -2.8799999999999999
      ],
      [ "C",
        64.010000000000005,
        24.260000000000002,
        65.519999999999996,
        22.75,
        67.390000000000001,
        22.390000000000001
      ],
      [ "L",
        67.390000000000001,
        22.390000000000001
      ],
      [ "z" ],
      [ "M",
        33.909999999999997,
        5.1799999999999997
      ],
      [ "c",
        -3.46,
        0.57999999999999996,
        -5.7599999999999998,
        3.96,
        -5.1100000000000003,
        7.5599999999999996
      ],
      [ "c",
        0.57999999999999996,
        3.6000000000000001,
        3.8900000000000001,
        6.0499999999999998,
        7.2699999999999996,
        5.4699999999999998
      ],
      [ "c",
        3.46,
        -0.57999999999999996,
        5.7599999999999998,
        -3.96,
        5.1799999999999997,
        -7.5599999999999996
      ],
      [ "C",
        40.609999999999999,
        7.0499999999999998,
        37.369999999999997,
        4.6100000000000003,
        33.909999999999997,
        5.1799999999999997
      ],
      [ "z" ]
    ],
  "scaleX" : 3.0299999999999998,
  "scaleY" : 3.0299999999999998,
  "selectable" : true,
  "stroke" : null,
  "strokeWidth" : 1,
  "top" : 220,
  "type" : "path",
  "width" : 99
}

你会有这个：

{ "angle" : 3,
  "fill" : "#00274D",
  "flipX" : false,
  "flipY" : false,
  "height" : 115,
  "left" : 353,
  "opacity" : 1,
  "overlayFill" : null,
  "path" : "http://example.com",
  "scaleX" : 3.0299999999999998,
  "scaleY" : 3.0299999999999998,
  "selectable" : true,
  "stroke" : null,
  "strokeWidth" : 1,
  "top" : 220,
  "type" : "path",
  "width" : 99
}

注意数据的大小，以及通过用url替换路径块来实现相对较小的数据。

这是一个非常简单的形状的代表。

这里唯一的要求是在调用toDatalessObject / toDatalessJSON之前使用setSourcePath方法设置对象的“sourcePath”（“sourcePath”在内部复制到“path”）。

希望这能把事情搞清楚一点。