[WebAssembly, ArrayBuffer] Low-level input for structs?

[maierfelix]

[WebAssembly, ArrayBuffer] Low-level input for structs?

[maierfelix]

This is already possible:

let buf: ArrayBuffer = new ArrayBuffer(VkInstanceCreateInfo.byteLength);
let instanceInfo: VkInstanceCreateInfo = new VkInstanceCreateInfo({
  $memoryBuffer: buf,
  $memoryOffset: 0x0
});

I've added this when adding support for sub-structures - e.g. VkRect2D, where offset and extent are VkOffset2D structs using the same memory as VkRect2D, but with a different offset.

You can check the Default Properties section in the docs, for example here, which shows the underlying methods and properties for low-level access.

What you're probably most interested in are the $memoryBuffer and $memoryOffset properties and the reflect method, which synchronizes the JS Object with the ArrayBuffer.

Structs also come with a memoryLayout object, which describes the byteOffset and byteLength of each struct member, e.g.:

VkInstanceCreateInfo.byteLength = 0x40;
VkInstanceCreateInfo.memoryLayout = {
  sType: {
    byteOffset: 0x0,
    byteLength: 0x4
  },
  pNext: {
    byteOffset: 0x8,
    byteLength: 0x8
  },
  ...
};

Also, if you're interested about how nvk works internally, checkout this file.

Edit:
I'm not sure your question is exactly about this, but I've also created a package callced nvk-struct-cache to mimic stack allocation when working with nvk, to reduce heap pressure.

I'm getting some skills and experience for professional purposes. Just interesting how work these worlds together. So, I trying to combine NVK with AssemblyScript (and run from that script language)…

UPDATE! Needs getAddressFromArrayBuffer and getArrayBufferFromAddress a public, because natively WebAssembly can't handle alike C++ pointers (i.e. addressing "limited" local-memory). Ah, I found that way...

[maierfelix]

nvk extends the ArrayBuffer Object with additional low-level methods - see the docs here

Note that one minor problem with Wasm is that it is in a fixed 32bit world, while NAPI is 64bit, so when you fill a Vulkan struct in Wasm, the memory doesn't align correctly.

I don't know your Wasm setup, but you might do it like this (pseudo code):

Setup:

let heap = new ArrayBuffer(2<<15);
let heapU32 = new Uint32Array(heap);
let module = new WebAssembly.Module(buffer);
let instance = new WebAssembly.Instance(module);

In C or AssemblyScript:

int test() {
  VkInstanceCreateInfo* info = (VkInstanceCreateInfo*) malloc(sizeof(VkInstanceCreateInfo));
  return (int) info;
}

In JS:

let infoAddr = instance.test();
let infoAddrView = new VkInstanceCreateInfo({
  $memoryBuffer: heap,
  $memoryOffset: infoAddr
});

I already tried to use with AssemblyScript and custom methods (with structure's). I found some critical bugs when create VkInstanceCreateInfo from WebAssembly memory with offset: no extension layers lists, application crash with that structure. I checked alignment, but has correct. Probably, there is internal "get" and "set" issues. Also in WASM structures I used globalify hack for pointers.