CanvasRenderingContext2D.quadraticCurveTo() - Web APIs 编辑

The CanvasRenderingContext2D.quadraticCurveTo() method of the Canvas 2D API adds a quadratic Bézier curve to the current sub-path. It requires two points: the first one is a control point and the second one is the end point. The starting point is the latest 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 coordinate of the control point.

cpy

The y-axis coordinate of the control point.

x

The x-axis coordinate of the end point.

y

The y-axis coordinate of the end point.

Examples

How quadraticCurveTo works

This example shows how a quadratic Bézier curve is drawn.

HTML

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

JavaScript

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

// Quadratic Bézier curve
ctx.beginPath();
ctx.moveTo(50, 20);
ctx.quadraticCurveTo(230, 30, 50, 100);
ctx.stroke();

// Start and end points
ctx.fillStyle = 'blue';
ctx.beginPath();
ctx.arc(50, 20, 5, 0, 2 * Math.PI);   // Start point
ctx.arc(50, 100, 5, 0, 2 * Math.PI);  // End point
ctx.fill();

// Control point
ctx.fillStyle = 'red';
ctx.beginPath();
ctx.arc(230, 30, 5, 0, 2 * Math.PI);
ctx.fill();

Result

In this example, the control point is red and the start and end points are blue.

A simple quadratic curve

This example draws a simple quadratic Bézier curve using quadraticCurveTo().

HTML

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

JavaScript

The curve begins at the point specified by moveTo(): (20, 110). The control point is placed at (230, 150). The curve ends at (250, 20).

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');

ctx.beginPath();
ctx.moveTo(20, 110);
ctx.quadraticCurveTo(230, 150, 250, 20);
ctx.stroke();

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The interface defining this method: CanvasRenderingContext2D
• Wikipedia article on Bézier curves