CanvasRenderingContext2D.bezierCurveTo()

The CanvasRenderingContext2D.bezierCurveTo() method of the Canvas 2D API adds a cubic Bézier curve to the path. It requires three points. The first two points are control points and the third one is the end point. The starting point is the last point in the current path, which can be changed using moveTo() before creating the Bézier curve.

Syntax

void ctx.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y);

Parameters

cp1x

The x coordinate of the first control point.

cp1y

The y coordinate of the first control point.

cp2x

The x coordinate of the second control point.

cp2y

The y coordinate of the second control point.

x

The x coordinate of the end point.

y

The y coordinate of the end point.

Examples

Using the bezierCurveTo method

This is just a simple code snippet drawing a bezier curve. The control points are red and the start and end points are blue.

HTML

<canvas id="canvas"></canvas>

JavaScript

//  Define Canvas & Context
    var canvas = document.getElementById('canvas');
    var context = canvas.getContext('2d');

//  Define the Points as {x,y}
    var start=    { x: 50,    y: 20 };
    var cp1=    { x: 230,    y: 30 };
    var cp2=    { x: 150,    y: 60 };
    var end=    { x: 50,    y: 100 };

//  Draw Curve
    context.beginPath();
    context.moveTo(start.x,start.y);
    context.bezierCurveTo(cp1.x, cp1.y, cp2.x, cp2.y, end.x, end.y);
    context.stroke();

//  Start & End Points
    context.fillStyle = 'blue';
    context.beginPath();
    context.arc(start.x, start.y, 5, 0, 2*Math.PI);
    context.arc(end.x, end.y, 5, 0, 2*Math.PI);
    context.fill();

//  Control Points
    context.fillStyle = 'red';
    context.beginPath();
    context.arc(cp1.x, cp1.y, 5, 0, 2*Math.PI);
    context.arc(cp2.x, cp2.y, 5, 0, 2*Math.PI);
    context.fill();

Trying the bezierCurveTo parameters

Edit the code below and see your changes update live in the canvas:

<canvas id="canvas" width="400" height="200" class="playable-canvas"></canvas>
<div class="playable-buttons">
  <input id="edit" type="button" value="Edit" />
  <input id="reset" type="button" value="Reset" />
</div>
<textarea id="code" class="playable-code">
ctx.beginPath();
ctx.bezierCurveTo(50, 100, 180, 10, 20, 10);
ctx.stroke();</textarea>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var edit = document.getElementById("edit");
var code = textarea.value;

function drawCanvas() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  eval(textarea.value);
}

reset.addEventListener("click", function() {
  textarea.value = code;
  drawCanvas();
});

edit.addEventListener("click", function() {
  textarea.focus();
})

textarea.addEventListener("input", drawCanvas);
window.addEventListener("load", drawCanvas);

Specifications

Browser compatibility

See also

• The interface defining it, CanvasRenderingContext2D
• WikiPedia article on Bézier curves.