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How to Draw Smooth Curve Through Multiple Points using JavaScript?
In this article, we will learn how to draw smooth a curve through multiple points using JavaScript with the help of canvas browser API and HTML element.
When it comes to visualizing data or creating interactive graphics on the web, drawing smooth curves through multiple points can greatly enhance the aesthetics and readability of the information. Let’s understand how to implement this with the help of some examples.
Example 1
In this example, we will leverage the concept of Brazier Curves which are defined by a set of control points to draw a smooth curve passing through them. We will predefine the points through which we will draw out our smooth curve using the canvas HTML element and its context API.
Filename: index.html
<html lang="en">
<head>
<title>
How to Draw Smooth Curve Through Multiple Points using JavaScript?
</title>
<style>
canvas {
border: 1px solid #000;
}
</style>
</head>
<body>
<canvas id="myCanvas" width="500" height="300"></canvas>
<script>
const canvas = document.getElementById("myCanvas");
const context = canvas.getContext("2d");
const points = [
{ x: 50, y: 100 },
{ x: 150, y: 200 },
{ x: 250, y: 50 },
{ x: 350, y: 150 },
{ x: 450, y: 100 },
];
function drawSmoothCurve(points) {
context.beginPath();
context.moveTo(points[0].x, points[0].y);
for (let i = 1; i < points.length - 1; i++) {
const xc = (points[i].x + points[i + 1].x) / 2;
const yc = (points[i].y + points[i + 1].y) / 2;
context.quadraticCurveTo(points[i].x, points[i].y, xc, yc);
}
// Connect the last two points with a straight line
context.lineTo(points[points.length - 1].x, points[points.length - 1].y);
context.stroke();
}
drawSmoothCurve(points);
</script>
</body>
</html>
Example 2
In this example, we will follow the above code structure and draw a smooth curve through multiple points using Bézier Curves and Catmull-Rom Splines methods.
Filename: index.html
<html lang="en">
<head>
<title>How to Draw Smooth Curve Through Multiple Points using JavaScript?</title>
<style>
canvas {
border: 1px solid #000;
}
</style>
</head>
<body>
<canvas id="myCanvas" width="500" height="300"></canvas>
<script>
const canvas = document.getElementById("myCanvas");
const context = canvas.getContext("2d");
const points = [
{ x: 50, y: 100 },
{ x: 150, y: 200 },
{ x: 250, y: 50 },
{ x: 350, y: 150 },
{ x: 450, y: 100 },
];
function drawSmoothCurve(points) {
context.beginPath();
context.moveTo(points[0].x, points[0].y);
// Example 1: Bézier Curves
// context.quadraticCurveTo(cp1x, cp1y, x, y);
// context.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y);
for (let i = 1; i < points.length - 1; i++) {
const xc = (points[i].x + points[i + 1].x) / 2;
const yc = (points[i].y + points[i + 1].y) / 2;
context.quadraticCurveTo(points[i].x, points[i].y, xc, yc);
}
// Connect the last two points with a straight line
context.lineTo(points[points.length - 1].x, points[points.length - 1].y);
context.stroke();
}
drawSmoothCurve(points);
// Example 2: Catmull-Rom Splines
function catmullRomSpline(points, context) {
context.beginPath();
context.moveTo(points[0].x, points[0].y);
for (let i = 1; i < points.length - 2; i++) {
const p0 = points[i - 1];
const p1 = points[i];
const p2 = points[i + 1];
const p3 = points[i + 2];
const t = 0.5;
const x1 = (-t * p0.x + (2 - t) * p1.x + (t - 2) * p2.x + t * p3.x) / 2;
const y1 = (-t * p0.y + (2 - t) * p1.y + (t - 2) * p2.y + t * p3.y) / 2;
const x2 = ((2 * t - 3) * p0.x + (3 - 4 * t) * p1.x + (1 + 2 * t) * p2.x + (-t) * p3.x) / 2;
const y2 = ((2 * t - 3) * p0.y + (3 - 4 * t) * p1.y + (1 + 2 * t) * p2.y + (-t) * p3.y) / 2;
const x3 = (t * p1.x + (2 - t) * p2.x) / 2;
const y3 = (t * p1.y + (2 - t) * p2.y) / 2;
context.bezierCurveTo(x1, y1, x2, y2, x3, y3);
}
context.lineTo(points[points.length - 2].x, points[points.length - 2].y);
context.lineTo(points[points.length - 1].x, points[points.length - 1].y);
context.stroke();
}
catmullRomSpline(points, context);
</script>
</body>
</html>
Conclusion
In conclusion, drawing smooth curves through multiple points using JavaScript can greatly enhance the visual aesthetics and readability of web-based graphics and data visualizations. By leveraging the power of Bezier curves, and Catmull-Rom Splines curves, we learned how to draw smooth curves through multiple points using javascript with the help of canvas HTML element and its context API.
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