Web/API/WebGLRenderingContext/readPixels

The WebGLRenderingContext.readPixels() method of the WebGL API reads a block of pixels from a specified rectangle of the current color framebuffer into an ArrayBufferView object.

Syntax

// WebGL1: 
void gl.readPixels(x, y, width, height, format, type, pixels); 

// WebGL2: 
void gl.readPixels(x, y, width, height, format, type, GLintptr offset); 
void gl.readPixels(x, y, width, height, format, type, ArrayBufferView pixels, GLuint dstOffset);

Parameters

x

A GLint specifying the first horizontal pixel that is read from the lower left corner of a rectangular block of pixels.

y

A GLint specifying the first vertical pixel that is read from the lower left corner of a rectangular block of pixels.

width

A GLsizei specifying the width of the rectangle.

height

A GLsizei specifying the height of the rectangle.

format

A GLenum specifying the format of the pixel data. Possible values:

gl.ALPHA: Discards the red, green and blue components and reads the alpha component.
gl.RGB: Discards the alpha components and reads the red, green and blue components.
gl.RGBA: Red, green, blue and alpha components are read from the color buffer.

WebGL2 adds

gl.RED
gl.RG
gl.RED_INTEGER
gl.RG_INTEGER
gl.RGB_INTEGER
gl.RGBA_INTEGER

type

A GLenum specifying the data type of the pixel data. Possible values:

gl.UNSIGNED_BYTE
gl.UNSIGNED_SHORT_5_6_5
gl.UNSIGNED_SHORT_4_4_4_4
gl.UNSIGNED_SHORT_5_5_5_1
gl.FLOAT

WebGL2 adds

gl.BYTE
gl.UNSIGNED_INT_2_10_10_10_REV
gl.HALF_FLOAT
gl.SHORT
gl.UNSIGNED_SHORT
gl.INT
gl.UNSIGNED_INT
gl.UNSIGNED_INT_10F_11F_11F_REV
gl.UNSIGNED_INT_5_9_9_9_REV

pixels

An ArrayBufferView object to read data into. The array type must match the type of the type parameter.

Uint8Array for gl.UNSIGNED_BYTE.
Uint16Array for gl.UNSIGNED_SHORT_5_6_5, gl.UNSIGNED_SHORT_4_4_4_4, or gl.UNSIGNED_SHORT_5_5_5_1.
Float32Array for gl.FLOAT.

dstOffset Optional

Offset. Defaults to 0.

Return value

None.

Exceptions

A gl.INVALID_ENUM error is thrown if format or type is not an accepted value.
A gl.INVALID_OPERATION error is thrown if
- type is gl.UNSIGNED_SHORT_5_6_5 and format is not gl.RGB.
- type is gl.UNSIGNED_SHORT_4_4_4_4 and format is not gl.RGBA.
- type does not match the typed array type of pixels.
A gl.INVALID_FRAMEBUFFER_OPERATION error is thrown if the currently bound framebuffer is not framebuffer complete.

Examples

var canvas = document.getElementById('canvas');
var gl = canvas.getContext('webgl');
var pixels = new Uint8Array(gl.drawingBufferWidth * gl.drawingBufferHeight * 4);
gl.readPixels(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight, gl.RGBA, gl.UNSIGNED_BYTE, pixels);
console.log(pixels); // Uint8Array

Specifications

Specification	Status	Comment
WebGL 1.0The definition of 'readPixels' in that specification.	Recommendation	Initial definition.
OpenGL ES 2.0The definition of 'glReadPixels' in that specification.	Standard	Man page of the OpenGL API.

Browser compatibility

The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`readPixels`	Chrome Full support 9	Edge Full support 12	Firefox Full support 4	IE Full support 11	Opera Full support 12	Safari Full support 5.1	WebView Android Full support Yes	Chrome Android Full support 25	Firefox Android Full support Yes	Opera Android Full support 12	Safari iOS Full support 8	Samsung Internet Android Full support 1.5
`WebGL2`	Chrome Full support 56	Edge Full support 79	Firefox Full support 51	IE No support No	Opera Full support 43	Safari No support No	WebView Android Full support 58	Chrome Android Full support 58	Firefox Android Full support 51	Opera Android Full support 43	Safari iOS No support No	Samsung Internet Android Full support 7.0

Legend

Full support: Full support
No support: No support