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Draw Control points for quadratic Bezier curve in JavaScript

Description

The following code shows how to draw Control points for quadratic Bezier curve.

Example


<!DOCTYPE HTML>
<html>
<head>
</head><!--  www  . j  a  v  a  2 s  . c  o m-->
<body>
<canvas id="canvas" width="500" height="840"></canvas>
<script>
var canvasElem = document.getElementById("canvas");
var ctx = canvasElem.getContext("2d");
var startPoint = [ 150, 100 ];
var endPoint = [ 400, 100 ];
var cp1 = [ 250, 50 ];
draw();
function draw() {
ctx.lineWidth = 3;
ctx.strokeStyle = "red";
ctx.beginPath();
ctx.moveTo(startPoint[0], startPoint[1]);
ctx.quadraticCurveTo(cp1[0], cp1[1], endPoint[0], endPoint[1]);
ctx.stroke();
ctx.lineWidth = 1;
ctx.strokeStyle = "red";
var points = [ startPoint, endPoint, cp1 ];
for ( var i = 0; i < points.length; i++) {
drawPoint(points[i]);
}
drawLine(startPoint, cp1);
drawLine(endPoint, cp1);
}
function drawPoint(point) {
ctx.beginPath();
ctx.strokeRect(point[0] - 2, point[1] - 2, 4, 4);
}
function drawLine(from, to) {
ctx.beginPath();
ctx.moveTo(from[0], from[1]);
ctx.lineTo(to[0], to[1]);
ctx.stroke();
}
</script>
</body>
</html>

Click to view the demo

The code above generates the following result.

Draw Control points for quadratic Bezier curve in JavaScript
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