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https://github.com/GoogleChromeLabs/buffer-backed-object

Buffer-backed objects in JavaScript.
https://github.com/GoogleChromeLabs/buffer-backed-object

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Buffer-backed objects in JavaScript.

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README 

        
# `BufferBackedObject`



**`BufferBackedObject` creates objects that are backed by an `ArrayBuffer`**. It takes a schema definition and de/serializes data on-demand using [`DataView`][dataview] under the hood. The goal is to make [`ArrayBuffer`][arraybuffer]s more convenient to use.



```

npm i -S buffer-backed-object

```



## Why?



### Web Workers



When using [Web Workers], the performance of `postMessage()` (or the [structured clone algorithm][structured clone] to be exact) is often a concern. While [`postMessage()` is a lot faster than most people give it credit for][is postmessage slow], it can still occasionally be a bottle-neck, especially with bigger payloads. [`ArrayBuffer`][arraybuffer] and their [views][arraybufferview] are incredibly quick to clone (or can even be [transferred][transferable]), but getting data in and out of `ArrayBuffer`s can be cumbersome. `BufferBackedObject` makes this easy by giving you a (seemingly) normal JavaScript object that reads and write values from the `ArrayBuffer` on demand. This means that the serialization & deserialization costs are deferred to the point of access rather than paid upfront, as it is the case with `postMessage()`.



### WebGL



[WebGL Buffers][webgl buffer] can store multiple attributes per vertex using [`vertexAttribPointer()`][vertexattribpointer]. These attributes can be a 3D position, but also other additional data like a normal vector, a color or a texture ID. The underlying buffer contains all the attributes for all the vertices in an interleaved format, which can make manipulating that data quite hard. With `ArrayOfBufferBackedObjects` you can manipulate each vertex individually. Additionally, `ArrayOfBufferBackedObjects` is populated lazily (see more below), allowing you to handle big arrays of vertices more efficiently.



### WebGPU



Similary, you can define structs in WGLS and read from/write to GPU memory buffers. With `BufferBackedObject` or `ArrayOfBufferBackedObjects`, you can manipulate those structs from JavaScript more easily and efficiently.



## Example



```js

import * as BBO from "buffer-backed-object";



const buffer = new ArrayBuffer(100);

const view = BBO.BufferBackedObject(buffer, {

  id: BBO.BufferBackedObject.Uint16({ endianness: "big" }),

  position: BBO.NestedBufferBackedObject({

    x: BBO.Float32(),

    y: BBO.Float32(),

    z: BBO.Float32(),

  }),

  normal: BBO.NestedBufferBackedObject({

    x: BBO.Float32(),

    y: BBO.Float32(),

    z: BBO.Float32(),

  }),

  textureId: BBO.Uint8(),

});



view.id = 3;

console.log(new Uint8Array(buffer));

// logs: Uint8Array(100) [3, 0, ...]

console.log(JSON.stringify(view));

// logs: {"id": 3, "position": {"x": 0, ...}, ...}

```



`ArrayOfBufferBackedObjects` interprets the given `ArrayBuffer` as an _array_ of objects with the given schema:



```js

import * as BBO from "buffer-backed-object";



const buffer = new ArrayBuffer(100);

const view = BBO.ArrayOfBufferBackedObjects(buffer, {

  id: BBO.Uint16({ endianness: "big" }),

  position: BBO.NestedBufferBackedObject({

    x: BBO.Float32(),

    y: BBO.Float32(),

    z: BBO.Float32(),

  }),

  normal: BBO.NestedBufferBackedObject({

    x: BBO.Float32(),

    y: BBO.Float32(),

    z: BBO.Float32(),

  }),

  textureId: BBO.Uint8(),

});



// The struct takes up a total of 27 bytes, so

// 3 structs can fit into a 100 byte `ArrayBuffer`.

console.log(view.length);

// logs: 3



view[0].id = 1000;

view[1].id = 1001;

view[2].id = 1002;

console.log(new Uint8Array(buffer));

// logs: Uint8Array(100) [232, 3, ...]

console.log(JSON.stringify(view));

// logs: [{"id": 1000, ...}, {"id": 1001}, ...]

```



## API



The module has the following exports:



### `function BufferBackedObject(buffer, descriptors, {byteOffset = 0})`



The key/value pairs in the `descriptors` object must be declared in the same order as they are laid out in the buffer. The returned object has getters and setters for each of `descriptors` properties and de/serializes them `buffer`, starting at the given `byteOffset`.



### `function ArrayOfBufferBackedObjects(buffer, descriptors, {byteOffset = 0, length = 0})`



Like `BufferBackedObject`, but returns an _array_ of `BufferBackedObject`s. If `length` is 0, as much of the buffer is used as possible. The array is populated lazily under the hood for performance purposes. That is, the individual `BufferBackedObject`s will only be created when their index is accessed.



### `function structSize(descriptors)`



Returns the number of bytes required to store a value with the schema outlined by `descriptors`.



### Descriptors



The following descriptor types are available as individually exported functions



- `function reserved(numBytes)`: A number of unused bytes. This field will now show up in the object.

- `function Int8()`: An 8-bit signed integer

- `function Uint8()`: An 8-bit unsigned integer

- `function Int16({align = 2, endianness = 'little'})`: An 16-bit signed integer

- `function Uint16({align = 2, endianness = 'little'})`: An 16-bit unsigned integer

- `function Int32({align = 4, endianness = 'little'})`: An 32-bit signed integer

- `function Uint32({align = 4, endianness = 'little'})`: An 32-bit unsigned integer

- `function BigInt64({align = 8, endianness = 'little'})`: An 64-bit signed [`BigInt`][bigint]

- `function BigUint64({align = 8, endianness = 'little'})`: An 64-bit unsigned [`BigInt`][bigint]

- `function Float32({align = 4, endianness = 'little'})`: An 32-bit IEEE754 float

- `function Float64({align = 8, endianness = 'little'})`: An 64-bit IEEE754 float (“double”)

- `function UTF8String(maxBytes)`: A UTF-8 encoded string with the given maximum number of bytes. Trailing NULL bytes will be trimmed after decoding.

- `function NestedBufferBackedObject(descriptors)`: A nested `BufferBackedObject` with the given descriptors

- `function NestedArrayOfBufferBackedObjects(numItems, descriptors)`: A nested `ArrayOfBufferBackedObjects` of length `numItems` with the given descriptors



## Defining your own descriptor types



All the descriptor functions return an object with the following structure:



```js

{

  align?: 1, // Required aligment

  size: 4, // Size required by the type

  get(dataView, byteOffset) {

    // Decode the value at byteOffset using

    // `dataView` or `dataView.buffer` and

    // return it.

  },

  set(dataView, byteOffset, value) {

    // Store `value` at `byteOffset` using

    // `dataView` or `dataView.buffer`.

  }

}

```



---



License Apache-2.0



[dataview]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView

[arraybuffer]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer

[web workers]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API

[structured clone]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm

[is postmessage slow]: https://surma.dev/things/is-postmessage-slow/

[arraybufferview]: https://developer.mozilla.org/en-US/docs/Web/API/ArrayBufferView

[transferable]: https://developer.mozilla.org/en-US/docs/Web/API/Transferable

[bigint]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt

[webgl buffer]: https://developer.mozilla.org/en-US/docs/Web/API/WebGLBuffer

[vertexattribpointer]: https://developer.mozilla.org/en-US/docs/Web/API/WebGLRenderingContext/vertexAttribPointer