Modify Curves with Anchor Points

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Instructions: Use your mouse or finger and drag and drop the anchor points to
modify the curvature of the quadratic curve and the Bezier curve.

Konva Modify Curves with Anchor Points Demoview raw
<!DOCTYPE html>
<html>
  <head>
    <script src="https://unpkg.com/konva@4.0.18/konva.min.js"></script>
    <meta charset="utf-8" />
    <title>Konva Modify Curves with Anchor Points Demo</title>
    <style>
      body {
        margin: 0;
        padding: 0;
        overflow: hidden;
        background-color: #f0f0f0;
      }
    </style>
  </head>
  <body>
    <div id="container"></div>
    <script>
      var width = window.innerWidth;
      var height = window.innerHeight;

      // globals
      var curveLayer, lineLayer, anchorLayer, quad, bezier;

      function updateDottedLines() {
        var q = quad;
        var b = bezier;

        var quadLine = lineLayer.findOne('#quadLine');
        var bezierLine = lineLayer.findOne('#bezierLine');

        quadLine.points([
          q.start.attrs.x,
          q.start.attrs.y,
          q.control.attrs.x,
          q.control.attrs.y,
          q.end.attrs.x,
          q.end.attrs.y
        ]);

        bezierLine.points([
          b.start.attrs.x,
          b.start.attrs.y,
          b.control1.attrs.x,
          b.control1.attrs.y,
          b.control2.attrs.x,
          b.control2.attrs.y,
          b.end.attrs.x,
          b.end.attrs.y
        ]);
        lineLayer.draw();
      }
      function buildAnchor(x, y) {
        var anchor = new Konva.Circle({
          x: x,
          y: y,
          radius: 20,
          stroke: '#666',
          fill: '#ddd',
          strokeWidth: 2,
          draggable: true
        });

        // add hover styling
        anchor.on('mouseover', function() {
          document.body.style.cursor = 'pointer';
          this.strokeWidth(4);
          anchorLayer.draw();
        });
        anchor.on('mouseout', function() {
          document.body.style.cursor = 'default';
          this.strokeWidth(2);
          anchorLayer.draw();
        });

        anchor.on('dragend', function() {
          drawCurves();
          updateDottedLines();
        });

        anchorLayer.add(anchor);
        return anchor;
      }
      function drawCurves() {
        var context = curveLayer.getContext();

        context.clear();

        // draw quad
        context.beginPath();
        context.moveTo(quad.start.attrs.x, quad.start.attrs.y);
        context.quadraticCurveTo(
          quad.control.attrs.x,
          quad.control.attrs.y,
          quad.end.attrs.x,
          quad.end.attrs.y
        );
        context.setAttr('strokeStyle', 'red');
        context.setAttr('lineWidth', 4);
        context.stroke();

        // draw bezier
        context.beginPath();
        context.moveTo(bezier.start.attrs.x, bezier.start.attrs.y);
        context.bezierCurveTo(
          bezier.control1.attrs.x,
          bezier.control1.attrs.y,
          bezier.control2.attrs.x,
          bezier.control2.attrs.y,
          bezier.end.attrs.x,
          bezier.end.attrs.y
        );
        context.setAttr('strokeStyle', 'blue');
        context.setAttr('lineWidth', 4);
        context.stroke();
      }

      var stage = new Konva.Stage({
        container: 'container',
        width: width,
        height: height
      });

      anchorLayer = new Konva.Layer();
      lineLayer = new Konva.Layer();

      // curveLayer just contains a canvas which is drawn
      // onto with the existing canvas API
      curveLayer = new Konva.Layer();

      var quadLine = new Konva.Line({
        dash: [10, 10, 0, 10],
        strokeWidth: 3,
        stroke: 'black',
        lineCap: 'round',
        id: 'quadLine',
        opacity: 0.3,
        points: [0, 0]
      });

      var bezierLine = new Konva.Line({
        dash: [10, 10, 0, 10],
        strokeWidth: 3,
        stroke: 'black',
        lineCap: 'round',
        id: 'bezierLine',
        opacity: 0.3,
        points: [0, 0]
      });

      // add dotted line connectors
      lineLayer.add(quadLine);
      lineLayer.add(bezierLine);

      quad = {
        start: buildAnchor(60, 30),
        control: buildAnchor(240, 110),
        end: buildAnchor(80, 160)
      };

      bezier = {
        start: buildAnchor(280, 20),
        control1: buildAnchor(530, 40),
        control2: buildAnchor(480, 150),
        end: buildAnchor(300, 150)
      };

      // keep curves insync with the lines
      anchorLayer.on('beforeDraw', function() {
        drawCurves();
        updateDottedLines();
      });

      stage.add(curveLayer);
      stage.add(lineLayer);
      stage.add(anchorLayer);

      drawCurves();
      updateDottedLines();
    </script>
  </body>
</html>
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