CanvasRenderingContext2D.clearRect() - Web APIs 编辑

The CanvasRenderingContext2D.clearRect() method of the Canvas 2D API erases the pixels in a rectangular area by setting them to transparent black.

Note: Be aware that clearRect() may cause unintended side effects if you're not using paths properly. Make sure to call beginPath() before starting to draw new items after calling clearRect().

Syntax

void ctx.clearRect(x, y, width, height);

The clearRect() method sets the pixels in a rectangular area to transparent black (rgba(0,0,0,0)). The rectangle's corner is at (x, y), and its size is specified by width and height.

Parameters

x

The x-axis coordinate of the rectangle's starting point.

y

The y-axis coordinate of the rectangle's starting point.

width

The rectangle's width. Positive values are to the right, and negative to the left.

height

The rectangle's height. Positive values are down, and negative are up.

Examples

Erasing the whole canvas

This code snippet erases the entire canvas. This is commonly required at the start of each frame in an animation. The dimensions of the cleared area are set to equal the <canvas> element's width and height attributes.

const canvas = document.getElementById('canvas');
const ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);

Erasing part of a canvas

This example draws a blue triangle on top of a yellowish background. The clearRect() method then erases part of the canvas.

HTML

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

JavaScript

The cleared area is rectangular in shape, with its top-left corner at (10, 10). The cleared area has a width of 120 and a height of 100.

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

// Draw yellow background
ctx.beginPath();
ctx.fillStyle = '#ff6';
ctx.fillRect(0, 0, canvas.width, canvas.height);

// Draw blue triangle
ctx.beginPath();
ctx.fillStyle = 'blue';
ctx.moveTo(20, 20);
ctx.lineTo(180, 20);
ctx.lineTo(130, 130);
ctx.closePath();
ctx.fill();

// Clear part of the canvas
ctx.clearRect(10, 10, 120, 100);

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• The interface defining this method: CanvasRenderingContext2D
• CanvasRenderingContext2D.fillRect()
• CanvasRenderingContext2D.strokeRect()