WebGL2RenderingContext.getBufferSubData

The WebGL2RenderingContext.getBufferSubData() method of the WebGL 2 API reads data from a buffer binding point and writes them to an ArrayBuffer or SharedArrayBuffer.

Syntax

void gl.getBufferSubData(target, srcByteOffset, ArrayBufferView dstData, optional dstOffset, optional length);

Parameters

target

A GLenum specifying the binding point (target). Possible values:

• gl.ARRAY_BUFFER: Buffer containing vertex attributes, such as vertex coordinates, texture coordinate data, or vertex color data.
• gl.ELEMENT_ARRAY_BUFFER: Buffer used for element indices.
• gl.COPY_READ_BUFFER: Buffer for copying from one buffer object to another.
• gl.COPY_WRITE_BUFFER: Buffer for copying from one buffer object to another.
• gl.TRANSFORM_FEEDBACK_BUFFER: Buffer for transform feedback operations.
• gl.UNIFORM_BUFFER: Buffer used for storing uniform blocks.
• gl.PIXEL_PACK_BUFFER: Buffer used for pixel transfer operations.
• gl.PIXEL_UNPACK_BUFFER: Buffer used for pixel transfer operations.

srcByteOffset

A GLintptr specifying the byte offset from which to start reading from the buffer.

dstData

An ArrayBuffer or SharedArrayBuffer to which to write the buffer data.

srcOffset Optional

A GLuint specifying the element index offset where to start reading the buffer.

length Optional

A GLuint defaulting to 0.

Return value

None.

Exceptions

An INVALID_VALUE error is generated if:

• offset + returnedData.byteLength would extend beyond the end of the buffer
• returnedData is null
• offset is less than zero.

An INVALID_OPERATION error is generated if:

• zero is bound to target
• target is TRANSFORM_FEEDBACK_BUFFER, and any transform feedback object is currently active.

Examples

var buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

var arrBuffer = new ArrayBuffer(vertices.length * Float32Array.BYTES_PER_ELEMENT);
gl.getBufferSubData(gl.ARRAY_BUFFER, 0, arrBuffer);

Specifications

Specification	Status	Comment
WebGL 2.0 The definition of 'getBufferSubData' in that specification.	Editor's Draft	Initial definition.

Browser compatibility

See also

• WebGLRenderingContext.bufferData()
• WebGLRenderingContext.bufferSubData()
• WebGLRenderingContext.getBufferParameter()
• WebGL2RenderingContext.copyBufferSubData()