luma.gl

Buffer

A Buffer is a WebGL object that stores an chunk of memory allocated by the GPU. This memory can be accessed directly by the GPU and is used to store things like vertex data, pixel data retrieved from images or the framebuffer, etc. The Buffer class provides mechanism for allocating such memory, together with facilities for copying data to and from the GPU (usually via JavaScript typed arrays).

For additional information, see OpenGL Wiki.

Usage

import {Buffer} from '@luma.gl/core';

Creating a generic buffer

const buffer = new Buffer(gl);

Creating an elements buffer

const buffer = new Buffer(gl, {target: GL.ELEMENT_ARRAY_BUFFER});

Allocating memory in a buffer

const buffer = new Buffer(gl, {byteLength: 200});
const buffer = new Buffer(gl).initialize({byteLength: 200});

Allocating and initializing a buffer

const buffer = new Buffer(gl, {
  target: GL.ELEMENTS_ARRAY_BUFFER,
  data: new Uint32Array([1, 2, 3])
});
const buffer = new Buffer(gl, new Float32Array([1, 2, 3])); // Allocate+init 12 bytes of GPU memory
const buffer = new Buffer(gl, 200); // Allocate 200 bytes of GPU memory

Updating a buffer

const buffer = new Buffer(gl, {byteLength: 200})
buffer.subData(new Float32Array(...));

Copying data between buffers (WebGL2)

const sourceBuffer = ...
const destinationBuffer = ...

// To copy 32 bytes from sourceBuffer to destinationBuffer
destinationBuffer.copyData({sourceBuffer, size: 32});

// To copy 32 bytes from sourceBuffer at 8 byte offset into
// destinationBuffer at 16 byte offset.
destinationBuffer.copyData({
  sourceBuffer,
  readOffset: 8,
  writeOffset: 16,
  size: 32
});

Getting data from a buffer (WebGL2)

const buffer = ...;

// To get all the data from buffer
const data = buffer.getData();

// To get all the data from buffer starting from byteOffset 8
// into existing ArrayBufferView.
const existingArray = ...
const data = buffer.getData({dstData: existingArray, srcByteOffset: 8});
// Maximum possible elements will be copied based buffer and dstData size.

// To get 5 elements from source buffer starting from byteOffset 8
// into existing ArrayBufferView starting from 3rd element position.
const existingArray = ...
const data = buffer.getData({dstData: existingArray, srcByteOffset: 8, dstOffset: 3, length: 5});

Members

handle : WebGLBuffer

Holds the underlying WebGL object reference.

byteLength : Number

Number of bytes of allocated memory.

bytesUsed : Number

Same as byteLength unless the Buffer.reallocate has been called with a value smaller than the actual length of the buffer.

accessor : Accessor

Holds an Accessor instance. By default it contains type information that is automatically deducted from the type of data used to initialize the buffer, but the application can store any Accessor it wants with the Buffer. This can simplify handling of buffer related data in many basic use cases (e.g. when buffers are not shared by multiple attributes etc).

Constructor

Buffer(gl : WebGLRenderingContext, props : Object | TypedArray | Number)

Creates a new Buffer. Multiple signatures are supported:

const buffer = new Buffer(gl, {target, ...initOptions, accessor, ...accessorOptions});

• gl (WebGLRenderingContext) - gl context
• target= (GLenum, optional) - the type of buffer, see below.
• ...initOptions (Object) - options passed on to initialize.
• accessor - options used to create the accessor
• ...accessorOptions (DEPRECATED) - options passed on to setAccessor. Use accessor instead.

const buffer = new Buffer(gl, typedArray);

• gl (WebGLRenderingContext) - gl context
• typedArray - typed array with values that should be used to size and initialize the new GPU buffer. Short hand for new Buffer({data: typedArray}).

const buffer = new Buffer(gl, byteLength);

• gl (WebGLRenderingContext) - gl context
• byteLength - specifies the number of bytes that should be allocated (but not initialized). Short hand for new Buffer({byteLength}).

The newly constructed buffer will either be a an “element” buffer used for storing vertex indices, or a “generic” buffer that can be used to store other things. To create an element buffer, specify target: GL.ELEMENT_ARRAY_BUFFER. If target is not specified, it will be a generic buffer that can be used in a variety of situations.

• In WebGL1, the default target is GL.ARRAY_BUFFER which will work as a “generic” (i.e. non-element) buffer.
• In WebGL2, the default target is GL.COPY_READ_BUFFER which means the buffer can work either as a generic buffer and an element buffer. This will be determined when it is first used with (bound to) a specific target. From that point on, WebGL will consider it either as an element buffer or a generic buffer.

Methods

initialize(props : Object) : Buffer

Allocates and optionally initializes buffer memory/data store (releasing any previously allocated memory).

Also extracts characteristics of stored data, hints for vertex attribute.

Buffer.initialize({data, byteLength, usage=, dataType=, size=, accessor=, ...accessorOptions})
Buffer(gl, typedArray);
Buffer(gl, byteLength);

• data (ArrayBufferView) - contents
• byteLength (Number) - the size of the buffer object’s data store.
• usage=GL.STATIC_DRAW (GLenum) - Allocation hint for GPU driver.
• accessor (Object) - object with accessor props to be stored as accessor.
• ...accessorOptions (DEPRECATED) - parameters passed to setAccessor

reallocate(byteLength : Number) : Buffer

If necessary, increases buffer size to byteLength. Does not decrease the buffer’s size if already long enough.

• byteLength (Number) - the minimum size of the buffer object’s data store.

Returns:

• true - if reallocation happened (in which case any stored data was invalidated).
• false - if the Buffer was already big enough in which case any uploaded data remains intact.

subData({data , offset=, srcOffset=, length=}) : Buffer

Updates part or all of a buffer’s allocated memory.

Buffer.subData({data, offset=, srcOffset=, length=})

• data (ArrayBufferView) - length is inferred unless provided
• offset=0 - Offset into buffer
• srcOffset=0 - WebGL2: Offset into srcData
• length - WebGL2: Number of bytes to be copied

copyData(options : Object) : Buffer (WebGL2)

Copies part of the data of another buffer into this buffer. The copy happens on the GPU and is expected to be efficient.

Buffer.copyData({sourceBuffer, readOffset=, writeOffset=, size})

• options.sourceBuffer (Buffer) - the buffer to read data from.
• options.readOffset=0 (GLint) - byte offset from which to start reading from the buffer.
• options.writeOffset=0 (GLint) - byte offset from which to start writing to the buffer.
• options.size (GLsizei) - byte count, specifying the size of the data to be copied.

Note:

• readOffset, writeOffset and size must all be greater than or equal to zero.
• readOffset + sizereadOffset + size must not exceeed the size of the source buffer object
• writeOffset + sizewriteOffset + size must not exceeed the size of the buffer bound to writeTarget.
• If the source and destination are the same buffer object, then the source and destination ranges must not overlap.

getData() : TypedArray (WebGL2)

Reads data from buffer into an ArrayBufferView or SharedArrayBuffer.

Buffer.getData({dstData, srcByteOffset, srcOffset, length})

• dstData=null (ArrayBufferView

  SharedArrayBuffer

  null) - memory to which to write the buffer data. New ArrayBufferView allocated with correct type if not provided.

• srcByteOffset=0 (GLintptr) - byte offset from which to start reading from the buffer.
• srcOffset=0 (GLuint) - element index offset where to start reading the buffer.
• length=0 (GLuint) Optional, Element count to be copied, optimal value calculated when not provided.

Returns a typed array containing the data from the buffer (if dstData was supplied it will be returned, otherwise this will be a freshly allocated array).

getElementCount([accessor : Accessor]) : Number

Returns number of elements in the buffer. In a buffer created with Float32Array typed array, each float is an element and takes 4 bytes (or 32 bits).

setAccessor(accessor : Accessor | Object) : Buffer

Allows you to optionally describe the accessor properties of the data in the buffer. This does not affect the buffer itself, but if supplied can avoid having to supply this data again when you use this buffer as an attribute later (see VertexArray.setAttributes).

For details on accessor props, see the documentation for the Accessor class.

Types

Usage

Usage	WebGL2	WebGL1	Description
GL.STATIC_DRAW	Yes	Yes	Buffer will be used often and not change often. Contents are written to the buffer, but not read.
GL.DYNAMIC_DRAW	Yes	Yes	Buffer will be used often and change often. Contents are written to the buffer, but not read.
GL.STREAM_DRAW	Yes	Yes	Buffer will not be used often. Contents are written to the buffer, but not read.
GL.STATIC_READ	Yes	No	Buffer will be used often and not change often. Contents are read from the buffer, but not written.
GL.DYNAMIC_READ	Yes	No	Buffer will be used often and change often. Contents are read from the buffer, but not written.
GL.STREAM_READ	Yes	No	Buffer will not be used often. Contents are read from the buffer, but not written.
GL.STATIC_COPY	Yes	No	Buffer will be used often and not change often. Contents are neither written or read by the user.
GL.DYNAMIC_COPY	Yes	No	Buffer will be used often and change often. Contents are neither written or read by the user.
GL.STREAM_COPY	Yes	No	Buffer will be used often and not change often. Contents are neither written or read by the user.

Parameters

Parameter	Type	Value
GL.BUFFER_SIZE	GLint	The size of the buffer in bytes
GL.BUFFER_USAGE	GLenum	The usage pattern of the buffer

“Manually” Binding Buffers

If you are an experienced WebGL or OpenGL programmer you are probably used to constantly binding buffers. Buffer binding and unbinding is handled internal by luma.gl methods and applications typically do not need to bind buffers.

To support use cases integrating with external libraries or raw webgl code, it is of course possible to “manually” bind and unbind luma.gl Buffer instances:

const buffer = ...;
buffer.bind({target: GL.ARRAY_BUFFER});
...
buffer.unbind({target: GL.ARRAY_BUFFER});

WebGL2 examples

buffer.bind({target: GL.PIXEL_PACK_BUFFER});
buffer.bind({target: GL.PIXEL_UNPACK_BUFFER});
buffer.bind({target: GL.TRANSFORM_FEEDBACK_BUFFER, index: 0});
buffer.bind({target: GL.UNIFORM_BUFFER, index: 0, offset: ..., size: ...});
buffer.unbind({target: GL.UNIFORM_BUFFER, index: 0});

Remarks

• All instance methods in a buffer (unless they return some documented value) are chainable.
• While transferring memory between CPU and GPU takes some time, once the memory is available as a buffer on the GPU it can be very efficiently used as inputs and outputs by the GPU.

Note that in WebGL, there are two types of buffers:

• “element” buffers. These can only store vertex attributes with indices (a.k.a “elements”) and can only be used by binding them to the GL.ELEMENT_ARRAY_BUFFER before draw calls.
• “generic” buffers. These can be used interchangeably to store different types of data, including (non-index) vertex attributes.

For more on the GL.ELEMENT_ARRAY_BUFFER restrictions in WebGL, see this page for WebGL1 and this page for WebGL2.

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