Modify Curves with Anchor Points

How to modify line points with anchors?

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/[email protected]/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;

// function to build anchor point
function buildAnchor(x, y) {
var anchor = new Konva.Circle({
x: x,
y: y,
radius: 20,
stroke: '#666',
fill: '#ddd',
strokeWidth: 2,
draggable: true,
});
layer.add(anchor);

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

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

return anchor;
}

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

var layer = new Konva.Layer();
stage.add(layer);

// function to update line points from anchors
function updateDottedLines() {
var q = quad;
var b = bezier;

var quadLinePath = layer.findOne('#quadLinePath');
var bezierLinePath = layer.findOne('#bezierLinePath');

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

bezierLinePath.points([
b.start.x(),
b.start.y(),
b.control1.x(),
b.control1.y(),
b.control2.x(),
b.control2.y(),
b.end.x(),
b.end.y(),
]);
layer.draw();
}

// we will use custom shape for curve
var quadraticLine = new Konva.Shape({
stroke: 'red',
strokeWidth: 4,
sceneFunc: (ctx, shape) => {
ctx.beginPath();
ctx.moveTo(quad.start.x(), quad.start.y());
ctx.quadraticCurveTo(
quad.control.x(),
quad.control.y(),
quad.end.x(),
quad.end.y()
);
ctx.fillStrokeShape(shape);
},
});
layer.add(quadraticLine);

// we will use custom shape for curve
var bezierLine = new Konva.Shape({
stroke: 'blue',
strokeWidth: 5,
sceneFunc: (ctx, shape) => {
ctx.beginPath();
ctx.moveTo(bezier.start.x(), bezier.start.y());
ctx.bezierCurveTo(
bezier.control1.x(),
bezier.control1.y(),
bezier.control2.x(),
bezier.control2.y(),
bezier.end.x(),
bezier.end.y()
);
ctx.fillStrokeShape(shape);
},
});
layer.add(bezierLine);

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

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

// special objects to save references to anchors
var quad = {
start: buildAnchor(60, 30),
control: buildAnchor(240, 110),
end: buildAnchor(80, 160),
};

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

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