用fabric.js用二次曲线绘制双线

Question

我试图找出是否可以使用包含在 fabric.js (http://fabricjs.com/quadratic-curve) 中的二次曲线函数绘制一条双线（如附图）。 有谁知道这是否可能或已经做到了？ 谢谢

这是示例图片：

Answer 1

如果您只对视觉效果感兴趣，请查看此双重渲染解决方案。

var canvas = this.__canvas = new fabric.Canvas('c');
  fabric.Object.prototype.originX = fabric.Object.prototype.originY = 'center';

  canvas.on({
    'object:selected': onObjectSelected,
    'object:moving': onObjectMoving,
    'before:selection:cleared': onBeforeSelectionCleared,
    'after:render': rerender
  });

  (function drawQuadratic() {
 
    var line = new fabric.Path('M 65 0 Q 100, 100, 200, 0', { fill: '', stroke: 'black', strokeWidth: 6 });

    line.path[0][1] = 100;
    line.path[0][2] = 100;

    line.path[1][1] = 200;
    line.path[1][2] = 200;

    line.path[1][3] = 300;
    line.path[1][4] = 100;

    line.selectable = false;
    canvas.add(line);

    var p1 = makeCurvePoint(200, 200, null, line, null)
    p1.name = "p1";
    canvas.add(p1);

    var p0 = makeCurveCircle(100, 100, line, p1, null);
    p0.name = "p0";
    canvas.add(p0);

    var p2 = makeCurveCircle(300, 100, null, p1, line);
    p2.name = "p2";
    canvas.add(p2);

  })();

  function makeCurveCircle(left, top, line1, line2, line3) {
    var c = new fabric.Circle({
      left: left,
      top: top,
      strokeWidth: 5,
      radius: 12,
      fill: '#fff',
      stroke: '#666'
    });

    c.hasBorders = c.hasControls = false;

    c.line1 = line1;
    c.line2 = line2;
    c.line3 = line3;

    return c;
  }

  function makeCurvePoint(left, top, line1, line2, line3) {
    var c = new fabric.Circle({
      left: left,
      top: top,
      strokeWidth: 8,
      radius: 14,
      fill: '#fff',
      stroke: '#666'
    });

    c.hasBorders = c.hasControls = false;

    c.line1 = line1;
    c.line2 = line2;
    c.line3 = line3;

    return c;
  }

  function onObjectSelected(e) {
    var activeObject = e.target;

    if (activeObject.name == "p0" || activeObject.name == "p2") {
      activeObject.line2.animate('opacity', '1', {
        duration: 200,
        onChange: canvas.renderAll.bind(canvas),
      });
      activeObject.line2.selectable = true;
    }
  }

  function onBeforeSelectionCleared(e) {
    var activeObject = e.target;
    if (activeObject.name == "p0" || activeObject.name == "p2") {
      activeObject.line2.animate('opacity', '0', {
        duration: 200,
        onChange: canvas.renderAll.bind(canvas),
      });
      activeObject.line2.selectable = false;
    }
    else if (activeObject.name == "p1") {
      activeObject.animate('opacity', '0', {
        duration: 200,
        onChange: canvas.renderAll.bind(canvas),
      });
      activeObject.selectable = false;
    }
  }
  function rerender() {
    var line = canvas.getObjects()[0];
    line.stroke = 'white';
    line.strokeWidth = 4;
    line.render(canvas.contextContainer);
    line.stroke = 'black';
    line.strokeWidth = 6;
  }
  function onObjectMoving(e) {
    if (e.target.name == "p0" || e.target.name == "p2") {
      var p = e.target;

      if (p.line1) {
        p.line1.path[0][1] = p.left;
        p.line1.path[0][2] = p.top;
      }
      else if (p.line3) {
        p.line3.path[1][3] = p.left;
        p.line3.path[1][4] = p.top;
      }
    }
    else if (e.target.name == "p1") {
      var p = e.target;

      if (p.line2) {
        p.line2.path[1][1] = p.left;
        p.line2.path[1][2] = p.top;
      }
    }
    else if (e.target.name == "p0" || e.target.name == "p2") {
      var p = e.target;

      p.line1 && p.line1.set({ 'x2': p.left, 'y2': p.top });
      p.line2 && p.line2.set({ 'x1': p.left, 'y1': p.top });
      p.line3 && p.line3.set({ 'x1': p.left, 'y1': p.top });
      p.line4 && p.line4.set({ 'x1': p.left, 'y1': p.top });
    }
  }

<script src="https://rawgithub.com/kangax/fabric.js/master/dist/fabric.js"></script>
<canvas id='c' width='500' height='500' ></canvas>