CanvasRenderingContext2D.quadraticCurveTo()

The CanvasRenderingContext2D.quadraticCurveTo() method of the Canvas 2D API adds a quadratic Bézier curve to the path. It requires two points. The first point is a control point and the second 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 quadratic Bézier curve.

Syntax

void ctx.quadraticCurveTo(cpx, cpy, x, y);

Parameters

cpx

The x axis of the coordinate for the control point.

cpy

The y axis of the coordinate for the control point.

x

The x axis of the coordinate for the end point.

y

The y axis of the coordinate for the end point.

Examples

Using the quadraticCurveTo method

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

HTML

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

JavaScript

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

ctx.beginPath();
ctx.moveTo(50,20);
ctx.quadraticCurveTo(230, 30, 50, 100);
ctx.stroke();

ctx.fillStyle = 'blue';
// start point
ctx.fillRect(50, 20, 10, 10);
// end point
ctx.fillRect(50, 100, 10, 10);

ctx.fillStyle = 'red';
// control point
ctx.fillRect(230, 30, 10, 10);

Trying the quadraticCurveTo 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.moveTo(50,20);
ctx.quadraticCurveTo(230, 30, 50, 100);
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.