UTexture2D::UpdateTextureRegions has no effect

Development Asset Creation
, ,
1

Hi!

I’m running UE4.18.1 PCD3D_SM5 on Win10 x64 Fall Creators Update (16299), GPU is GTX 750 Ti.

I develop yet another fog of war and have following code:

void AFogOfWar::BeginPlay()
{
    Super::BeginPlay();
    this->FogMapTexture = UTexture2D::CreateTransient(30, 60, EPixelFormat::PF_A8);
    FogMapTexture->UpdateResource();

    if (this->TargetVolume != nullptr)
    {

        UMaterialInstanceDynamic* MaterialInstance = UMaterialInstanceDynamic::Create(this->PostProcessMaterial, this);
        if (MaterialInstance != nullptr)
        {
            MaterialInstance->SetTextureParameterValue(TEXT("FogMapTexture"), FogMapTexture);
            TargetVolume->AddOrUpdateBlendable(MaterialInstance, 1.f);
        }

    }

}

void AFogOfWar::Tick(float DeltaTime)
{
    Super::Tick(DeltaTime);

    static struct FPayload {
        uint8 Data[30 * 60];
        FPayload() { memset(Data, 255, 30 * 60); }
    } Payload;
    
    static FUpdateTextureRegion2D region(0, 0, 0, 0, 30, 60);
    FogMapTexture->UpdateTextureRegions(0, 1, &region, 30, 1, Payload.Data);
    FogMapTexture->UpdateResource();
}

The problem is, UpdateTextureRegions has no effect on FogMapTexture, but direct modification of texture mip’s BulkData works nice although is not efficient:

void AFogOfWar::Tick(float DeltaTime)
{
    Super::Tick(DeltaTime);

    void* TextureData = FogMapTexture->PlatformData->Mips[0].BulkData.Lock(LOCK_READ_WRITE);

    for (uint32 iY = 0; iY < 60; ++iY)
    {
        FMemory::Memset((uint8*)TextureData + (iY * 30), 255, 30);
    }

    FogMapTexture->PlatformData->Mips[0].BulkData.Unlock();
    FogMapTexture->UpdateResource();
}

I came up with similar questions on AnswerHub and forums, but no proposed solutions seems working for me. How to use UpdateTextureRegions properly?

2

Finally found the solution and related pitfall on Setting Up a Dynamic Texture - #4 by anonymous_user_4827d1c0 - C++ - Epic Developer Community Forums

Before updating the regions, we must make sure the resource exists and is updated. I call UpdateResource() right after UTexture2D::CreateTransient as seen above, but UTexture2D::UpdateResource has no effect within AActor::BeginPlay!

We must UpdateResource within AActor::Tick, before first UpdateTextureRegions. This way the texture is created and initialized properly and we can modify/update it further.