将 float32 数组重新解释为 uint8 数组时字节数不匹配

Question

我们打算将 float32 值数组的 JavaScript 表示更改为 uint8 字节数组。这意味着这样做可能会帮助我们更有效地通过 HTTP 请求传输数据。

为此，我们尝试过：

var vertexBuffer = ...; // Float32Array
console.log('vertex buffer =', vertexBuffer);
console.log('vertex buffer byte length = ', vertexBuffer.byteLength)
var arr = new Uint8Array(vertexBuffer);
console.log('converted to Uint8Array: ', arr);
console.log('Byte length = ', arr.byteLength);
console.log('Byte length / 4 = ', arr.byteLength / 4);

日志是：

含义

Float32Array 的大小是 84942，结果 Uint8Array 也是如此！

意味着每个 float32 值都转换为单个 uint8！这不是我们打算做的！对吧？

我们打算将每个 float32 解释为四个 uint8 值。我们怎样才能以最有效的方式做到这一点？解释的改变应该不需要任何计算吧？

Answer 1

It's implied that doing so might help us more efficiently transfer the data over HTTP requests.

情况并非如此，除非您确实希望将浮点值的精度截断为 8 位整数。只需通过您喜欢的任何方法发送数组的“原始数据”vertexArray.buffer（一个 ArrayBuffer）。（当然你可以在发送之前压缩数据，如果你不喜欢的话。）

然后，您可以通过将收到的 ArrayBuffer 传递给 Float32Array 构造函数来重建 Float32Array。

演示这些转换：

> arr = new Float32Array([Math.sqrt(2), Math.sqrt(3)])
// An array of 2 floats, 4 bytes each
Float32Array(2) [1.4142135381698608, 1.7320507764816284, buffer: ArrayBuffer(8), byteLength: 8, byteOffset: 0, length: 2]

> bytes = new Uint8Array(arr.buffer)
// The same floats but interpreted as 8-bit values (8 integers, 1 byte each)
Uint8Array(8) [243, 4, 181, 63, 215, 179, 221, 63, buffer: ArrayBuffer(8), byteLength: 8, byteOffset: 0, length: 8]

> bytes[1] = 123
// Modifying the byte array 
// (since an ArrayBuffer is just opaque memory, it can't be modified,
//  but we can modify the byte interpretation of it)
123

> new Float32Array(bytes.buffer)
// (this step is not strictly necessary; 
//  modifying `bytes` will have changed the underlying buffer
//  used by the original `Float32Array` since we didn't copy it)
// Reinterpreting the modified bytes as floats 
// (see how the first value has slightly changed)
Float32Array(2) [1.4178451299667358, 1.7320507764816284, buffer: ArrayBuffer(8), byteLength: 8, byteOffset: 0, length: 2]

将 float32 数组重新解释为 uint8 数组时字节数不匹配

Byte count mismatch when re-interpreting float32 array as uint8 array

javascript

arrays

uint8array

含义