How to use Huge Typed Array? about unreal.js

[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);
}

[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?