How to use Huge Typed Array?

[mflux]

Hi Nako, I seem to be running into speed issues passing large arrays from JS into Unreal. The size range is between 3000 to 16000 floats, for passing geometry data from JS to Unreal.

I'm 99% sure the speed loss is due to JS transfering data and needs to use: https://github.com/ncsoft/Unreal.js/wiki/Huge-typed-array

However, I'm uncertain how to actually pass to for example, ProceduralMesh component's UpdateMeshSection function.

I'm comfortable enough with C++ do dive in however this is still confusing to me:

let ab = new ArrayBuffer(32*1024); // 32K bytes buffer
let u8 = new Uint8Array(ab); // typed array
memory.bind(ab);
GWorld.MySuperMemoryFunction();
memory.unbind(ab);

What is MySuperMemoryFunction()? Is this compiled from somewhere? How do you go about creating that function? Is 'ab' variable supposed to be passed in?

void UMyBlueprintFunctionLibrary::MySuperMemoryFunction(UWorld* World)
{
    auto size = FArrayBufferAccessor::GetSize();
    auto buffer = FArrayBufferAccessor::GetData();
}

Is there just a single FArrayBufferAccessor that's bound as a global variable? What's the best way to go from here to ProceduralMesh's UpdateMeshSection?

[mflux]

Continuing from the above... I was able to get a BlueprintFunctionLibrary compiled, however FArrayBufferAccessor is not found.

According to some examples found in the Unreal.js plugin, it comes from one of these:

#include "JavascriptEditor.h"
#include "JavascriptEditorLibrary.h"

However the source for that is not accessible. Am I going about this the right way? Am I supposed to include the plugin source to have access to these functions?

[nakosung]

Array buffer accessor is located at 'JavascriptContext.h`. (https://github.com/ncsoft/Unreal.js-core/blob/master/Source/V8/Public/JavascriptContext.h)

If you want to read back from huge typed array (which is passed from C++), there is a working example. (https://github.com/nakosung/UnrealDarknet/blob/master/Content/Scripts/yolo.js)

[mflux]

Thanks Nako

What's the proper way to include JavascriptContext.h? Should I include all the project files for the plugin into my game project/folder?

[nakosung]

No. Add project dependency in your game.Build.cs. And add #include "JavascriptContext.h" in your cpp. :)

[nakosung]

https://github.com/nakosung/UnrealDarknet/blob/master/Source/darknet/darknet.Build.cs#L26

This is a working example.

[mflux]

Ah thanks! Add V8 instead of Unreal.js? How does Unreal's build system know where to look for this dependency? I currently have the V8 source in my Program Files/Epic/UE/4.1/plugin/UnrealJS/etc... folder. Does the path matter? Should it be inside my project folder instead?

[nakosung]

If you build engine from source, plugin can be installed as an engine plugin. I'm not sure with packaged build from epic.

[mflux]

Alright, will look into it, thanks!

[mflux]

I got it mostly working. It looks like memory.bind is deprecated?

Warning: memory.bind is deprecated. use memory.exec(ab,fn) instead.

Should it be like this?

let ab = new ArrayBuffer(32*1024); // 32K bytes buffer
let u8 = new Uint8Array(ab); // typed array
memory.exec(ab, function(){      
  return [someArrayofData];
});

//  BP-Library Function that uses memory
GWorld.FastArrayCopy();

I couldn't find any documentation of memory.exec.

The yolo.js example you linked https://github.com/nakosung/UnrealDarknet/blob/master/Content/Scripts/yolo.js made no use of memory.bind either.

Furthermore, the Hello.js example has this but it isn't clear to me how the memory value is being used afterwards:

Unreal.js/Examples/Content/Scripts/helloJS.js

Line 29 in 89e2fed

memory.exec(ab,_ => {

[nakosung]

Yes, unguarded operations are deprecated. :)

memory.exec(ab, function() {
  // all operations which accesses array buffer should be guarded within this function.
  GWorld.FastArrayCopy();
})

[mflux]

Haha. Yes, that seems much safer.

Are there examples of accessing the data inside a FArrayBufferAccessor? For example looping over it?

[mflux]

I figured it out 👍

In Javascript

let fa = Float32Array.from( [ 10000, 99999, 123456, 30.2000, 3.1419 ]); // typed array

memory.exec(fa.buffer, function(){
  GWorld.FastArrayCopy();
});

In C++

auto size = FArrayBufferAccessor::GetSize();
auto buffer = FArrayBufferAccessor::GetData();

float* conv = static_cast<float*>(buffer);
int length = size / 4;

UE_LOG(LogTemp, Log, TEXT("length of array %d"), length);
for (int i = 0; i < length; i++) {
    float f = float( conv[i]);
    UE_LOG(LogTemp, Log, TEXT("%f"), f);
}