如何在 fabric.js 中标记双头箭头的大小

Question

首先感谢this answer，解决了我画双箭头的问题

但是我在这个基础上还有一个问题：

如何在绘制双头箭头后添加一个Textbox来表示线的长度？
如何保持Textbox与直线平行？这意味着需要计算角度值。
以上两点完成后，LineArrow和Textbox如何用fabric.Group合并？

// Extended fabric line class
fabric.LineArrow = fabric.util.createClass(fabric.Line, {

  type: 'lineArrow',

  initialize: function(element, options) {
    options || (options = {});
    this.callSuper('initialize', element, options);
  },

  toObject: function() {
    return fabric.util.object.extend(this.callSuper('toObject'));
  },

  _render: function(ctx) {
    this.ctx = ctx;
    this.callSuper('_render', ctx);
    let p = this.calcLinePoints();
    let xDiff = this.x2 - this.x1;
    let yDiff = this.y2 - this.y1;
    let angle = Math.atan2(yDiff, xDiff);
    this.drawArrow(angle, p.x2, p.y2);
    ctx.save();
    xDiff = -this.x2 + this.x1;
    yDiff = -this.y2 + this.y1;
    angle = Math.atan2(yDiff, xDiff);
    this.drawArrow(angle, p.x1, p.y1);
  },

  drawArrow: function(angle, xPos, yPos) {
    this.ctx.save();
    this.ctx.translate(xPos, yPos);
    this.ctx.rotate(angle);
    this.ctx.beginPath();
    // Move 5px in front of line to start the arrow so it does not have the square line end showing in front (0,0)
    this.ctx.moveTo(10, 0);
    this.ctx.lineTo(-15, 15);
    this.ctx.lineTo(-15, -15);
    this.ctx.closePath();
    this.ctx.fillStyle = this.stroke;
    this.ctx.fill();
    this.ctx.restore();
  }
});



fabric.LineArrow.fromObject = function(object, callback) {
  callback && callback(new fabric.LineArrow([object.x1, object.y1, object.x2, object.y2], object));
};

fabric.LineArrow.async = true;


var Arrow = (function() {
  function Arrow(canvas) {
    this.canvas = canvas;
    this.className = 'Arrow';
    this.isDrawing = false;
    this.bindEvents();
  }

  Arrow.prototype.bindEvents = function() {
    var inst = this;
    inst.canvas.on('mouse:down', function(o) {
      inst.onMouseDown(o);
    });
    inst.canvas.on('mouse:move', function(o) {
      inst.onMouseMove(o);
    });
    inst.canvas.on('mouse:up', function(o) {
      inst.onMouseUp(o);
    });
    inst.canvas.on('object:moving', function(o) {
      inst.disable();
    })
  }

  Arrow.prototype.onMouseUp = function(o) {
    var inst = this;
    // Calculate the length of the LineArrow
    var a = this.line.x2 - this.line.x1
    var b = this.line.y2 - this.line.y1
    var lineLength = Math.floor(Math.sqrt(a * a + b * b));
    if (lineLength === 0) {
      inst.canvas.remove(this.line);
      return;
    }

    var textBox = new fabric.Textbox(lineLength.toFixed(), {
      hasBorders: true,
      hasControls: false,
      selectable: true,
      borderColor: 'red',
      fill: 'red',
      left: this.line.left,
      top: this.line.top
    }).setCoords();

    textBox.set('angle', this.line.angle / (Math.PI / 180));

    inst.canvas.add(textBox).setActiveObject(textBox);

    this.line.set({
      dirty: true,
      objectCaching: true
    });
    inst.canvas.renderAll();
    inst.disable();
  };

  Arrow.prototype.onMouseMove = function(o) {
    var inst = this;
    if (!inst.isEnable()) {
      return;
    }

    var pointer = inst.canvas.getPointer(o.e);
    var activeObj = inst.canvas.getActiveObject();
    activeObj.set({
      x2: pointer.x,
      y2: pointer.y
    });
    activeObj.setCoords();
    inst.canvas.renderAll();
  };

  Arrow.prototype.onMouseDown = function(o) {
    var inst = this;
    inst.enable();
    var pointer = inst.canvas.getPointer(o.e);

    var points = [pointer.x, pointer.y, pointer.x, pointer.y];
    this.line = new fabric.LineArrow(points, {
      strokeWidth: 5,
      fill: 'red',
      stroke: 'red',
      originX: 'center',
      originY: 'center',
      hasBorders: false,
      hasControls: false,
      objectCaching: false,
      perPixelTargetFind: true
    });

    inst.canvas.add(this.line).setActiveObject(this.line);
  };

  Arrow.prototype.isEnable = function() {
    return this.isDrawing;
  }

  Arrow.prototype.enable = function() {
    this.isDrawing = true;
  }

  Arrow.prototype.disable = function() {
    this.isDrawing = false;
  }

  return Arrow;
}());

var canvas = new fabric.Canvas('canvas', {
  selection: false
});
var arrow = new Arrow(canvas);

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.17/fabric.min.js"></script>
Please draw arrow here

<div id="canvasContainer">
  <canvas id="canvas" width="400" height="400" style="border: solid 1px"></canvas>
</div>

以上是我修改后的代码，其实并不完美，希望有人能帮帮我。

提前致谢。

Answer 1

至于问题 2，以下似乎适用于您的 onMouseUp 函数：

var angle = Math.atan2(this.line.y2 - this.line.y1, this.line.x2 - this.line.x1);

textBox.set('angle', angle / (Math.PI / 180));

所以，基本上我们计算箭头和 x-axis 之间的 atan 并相应地旋转。

问题 3 - 下面似乎有点把它打包成一个组，检查下面的代码片段是否有帮助（在你的 onMouseUp:

的底部

    var group = new fabric.Group();
    group.addWithUpdate(fabric.util.object.clone(this.line));
    group.addWithUpdate(textBox);
    inst.canvas.add(group).setActiveObject(group);
    inst.canvas.remove(this.line);
    inst.canvas.renderAll();
    inst.disable();

功能内容请见底部

这是一个汇总的片段：

// Extended fabric line class
fabric.LineArrow = fabric.util.createClass(fabric.Line, {

  type: 'lineArrow',

  initialize: function(element, options) {
    options || (options = {});
    this.callSuper('initialize', element, options);
  },

  toObject: function() {
    return fabric.util.object.extend(this.callSuper('toObject'));
  },

  _render: function(ctx) {
    this.ctx = ctx;
    this.callSuper('_render', ctx);
    let p = this.calcLinePoints();
    let xDiff = this.x2 - this.x1;
    let yDiff = this.y2 - this.y1;
    let angle = Math.atan2(yDiff, xDiff);
    this.drawArrow(angle, p.x2, p.y2);
    ctx.save();
    xDiff = -this.x2 + this.x1;
    yDiff = -this.y2 + this.y1;
    angle = Math.atan2(yDiff, xDiff);
    this.drawArrow(angle, p.x1, p.y1);
  },

  drawArrow: function(angle, xPos, yPos) {
    this.ctx.save();
    this.ctx.translate(xPos, yPos);
    this.ctx.rotate(angle);
    this.ctx.beginPath();
    // Move 5px in front of line to start the arrow so it does not have the square line end showing in front (0,0)
    this.ctx.moveTo(10, 0);
    this.ctx.lineTo(-15, 15);
    this.ctx.lineTo(-15, -15);
    this.ctx.closePath();
    this.ctx.fillStyle = this.stroke;
    this.ctx.fill();
    this.ctx.restore();
  }
});



fabric.LineArrow.fromObject = function(object, callback) {
  callback && callback(new fabric.LineArrow([object.x1, object.y1, object.x2, object.y2], object));
};

fabric.LineArrow.async = true;


var Arrow = (function() {
  function Arrow(canvas) {
    this.canvas = canvas;
    this.className = 'Arrow';
    this.isDrawing = false;
    this.bindEvents();
  }

  Arrow.prototype.bindEvents = function() {
    var inst = this;
    inst.canvas.on('mouse:down', function(o) {
      inst.onMouseDown(o);
    });
    inst.canvas.on('mouse:move', function(o) {
      inst.onMouseMove(o);
    });
    inst.canvas.on('mouse:up', function(o) {
      inst.onMouseUp(o);
    });
    inst.canvas.on('object:moving', function(o) {
      inst.disable();
    })
  }

  Arrow.prototype.onMouseUp = function(o) {
    var inst = this;
    // Calculate the length of the LineArrow
    var a = this.line.x2 - this.line.x1
    var b = this.line.y2 - this.line.y1
    var lineLength = Math.floor(Math.sqrt(a * a + b * b));
    if (lineLength === 0) {
      inst.canvas.remove(this.line);
      return;
    }

    var textBox = new fabric.Textbox(lineLength.toFixed(), {
      hasBorders: true,
      hasControls: false,
      selectable: true,
      borderColor: 'red',
      fill: 'red',
      left: this.line.left,
      top: this.line.top
    }).setCoords();
    
    var angle = Math.atan2(this.line.y2 - this.line.y1, this.line.x2 - this.line.x1);

    textBox.set('angle', angle / (Math.PI / 180));

    this.line.set({
      dirty: true,
      objectCaching: true
    });
    
    var group = new fabric.Group();
    group.addWithUpdate(fabric.util.object.clone(this.line));
    group.addWithUpdate(textBox);
    inst.canvas.add(group).setActiveObject(group);
    inst.canvas.remove(this.line);
    inst.canvas.renderAll();
    inst.disable();
  };

  Arrow.prototype.onMouseMove = function(o) {
    var inst = this;
    if (!inst.isEnable()) {
      return;
    }

    var pointer = inst.canvas.getPointer(o.e);
    var activeObj = inst.canvas.getActiveObject();
    activeObj.set({
      x2: pointer.x,
      y2: pointer.y
    });
    activeObj.setCoords();
    inst.canvas.renderAll();
  };

  Arrow.prototype.onMouseDown = function(o) {
    var inst = this;
    inst.enable();
    var pointer = inst.canvas.getPointer(o.e);

    var points = [pointer.x, pointer.y, pointer.x, pointer.y];
    this.line = new fabric.LineArrow(points, {
      strokeWidth: 5,
      fill: 'red',
      stroke: 'red',
      originX: 'center',
      originY: 'center',
      hasBorders: false,
      hasControls: false,
      objectCaching: false,
      perPixelTargetFind: true
    });

    inst.canvas.add(this.line).setActiveObject(this.line);
  };

  Arrow.prototype.isEnable = function() {
    return this.isDrawing;
  }

  Arrow.prototype.enable = function() {
    this.isDrawing = true;
  }

  Arrow.prototype.disable = function() {
    this.isDrawing = false;
  }

  return Arrow;
}());

var canvas = new fabric.Canvas('canvas', {
  selection: false
});
var arrow = new Arrow(canvas);

<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.17/fabric.min.js"></script>
Please draw arrow here

<div id="canvasContainer">
  <canvas id="canvas" width="400" height="400" style="border: solid 1px"></canvas>
</div>

至于第 1 点 - after 是什么意思，即。在之后还是space？ :D

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