[UE] FString和v8::String用UTF16传参，无需使用UTF8编码转换

[BlurryLight]

v8::String 支持用UTF-16存储字符串，不需要在JSEnv里传参的时候转成UTF-8。
见 https://v8.github.io/api/head/classv8_1_1String.html#aac41d1932f0897dace0a507abda6d49f

UE2JS:

v8::String::NewFromTwoByte(Isolate, TCHAR_TO_UTF16(String), v8::NewStringType::kNormal).ToLocalChecked();

JS2UE:

uint16_t* UTF16Bytes = *v8::String::Value(Isolate, Info[1]);
Result = FString(UTF16_TO_TCHAR(UTF16Bytes));

简单写了个benchmark,

static void UE2JSStringBenchMark(const v8::FunctionCallbackInfo<v8::Value>& Info)
{
    auto Isolate = Info.GetIsolate();
    v8::HandleScope HandleScope(Isolate);
    v8::Local<v8::Context> Context = Isolate->GetCurrentContext();

     FString ShortString = TEXT("我能吞下玻璃而不伤身体。");
     FString LongString(1000, TEXT("我能吞下玻璃而不伤身体。")) ;

    TArray<int, TInlineAllocator<32>> LoopNum{1'000, 10'000, 100'000, 1'000'000};
    for (auto loop : LoopNum)
    {
        for (int j = 0; j < 2; j++)
        {
            const FString& Str = j == 0 ? ShortString : LongString;
            UE_LOG(LogTemp, Log, TEXT("Convert V8 String %s, %d time"), j == 0 ? TEXT("ShortString") : TEXT("LongString"), loop);
            {
                SCOPE_LOG_TIME("Convert To UTF8", nullptr);
                for (int i = 0; i < loop; i++)
                {
                    FV8Utils::ToV8String(Isolate, *Str);
                }
            }
            {
                SCOPE_LOG_TIME("Convert To UTF16", nullptr);
                for (int i = 0; i < loop; i++)
                {
                    FV8Utils::ToV8String_UTF16(Isolate, *Str);
                }
            }
        }
        Isolate->RequestGarbageCollectionForTesting(v8::Isolate::kFullGarbageCollection);
    }
    auto Result = v8::Object::New(Isolate);
    Result->Set(Context, 0, FV8Utils::ToV8String(Isolate, *ShortString));
    Result->Set(Context, 1, FV8Utils::ToV8String_UTF16(Isolate, *ShortString));
    Info.GetReturnValue().Set(Result);
}

测试数据

Convert V8 String ShortString, 1000 time
                  Convert To UTF8 -  0.185 ms
                 Convert To UTF16 -  0.039 ms
Convert V8 String LongString, 1000 time
                  Convert To UTF8 -  0.187 ms
                 Convert To UTF16 -  0.035 ms
Convert V8 String ShortString, 10000 time
                  Convert To UTF8 -  1.872 ms
                 Convert To UTF16 -  0.341 ms
Convert V8 String LongString, 10000 time
                  Convert To UTF8 -  3.701 ms
                 Convert To UTF16 -  0.242 ms
Convert V8 String ShortString, 100000 time
                  Convert To UTF8 - 21.398 ms
                 Convert To UTF16 - 10.617 ms
Convert V8 String LongString, 100000 time
                  Convert To UTF8 - 16.938 ms
                 Convert To UTF16 - 20.640 ms
Convert V8 String ShortString, 1000000 time
                  Convert To UTF8 - 238.680 ms
                 Convert To UTF16 - 96.221 ms
Convert V8 String LongString, 1000000 time
                  Convert To UTF8 - 330.778 ms
                 Convert To UTF16 - 136.779 ms
Puerts: (0x000002A0174AE390) 我能吞下玻璃而不伤身体。
Puerts: (0x000002A0174AE390) 我能吞下玻璃而不伤身体。

[chexiongsheng]

早期试过，忘记什么原因放弃了。
我当时的性能测试用例也测试过：https://github.com/chexiongsheng/puerts_unreal_demo/blob/master/Source/puerts_unreal_demo/UTGUnitTestCalleeWrap.cpp#L63

你可以先试试。

[chexiongsheng]

你们在你们项目中验证这想法了么？

[BlurryLight]

铺开用了一段时间了，没啥问题。全部走UTF-16

[chexiongsheng]

那可以PR过来呀