Strange Access violation reading landscape texture

Development Programming & Scripting C++
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1

Hello,
I’ve got a plugin that reads the landscape heightmap into a texture and then extracts the texture data.
It reads the heightmap into a texture but then trying to read its contents into CPU causes an access violation. I do not understand why - the memcpy is done on the render thread.

asd
asd1505×890 66 KB

Creating the texture/RT

constexpr int gHeightmapSizeX = 1024;
constexpr int gHeightmapSizeY = 1024;

void FHeightmapToolModule::StartupModule()
{
	...

	_Heightmap = UTexture2D::CreateTransient( gHeightmapSizeX, gHeightmapSizeY, EPixelFormat::PF_G16 );
	_Heightmap->AddToRoot();
	_HeightMapRT = NewObject<UTextureRenderTarget2D>();
	_HeightMapRT->AddToRoot();
}

Reading the landscape heightmap into the texture

void FHeightmapToolModule::UpdateTextureFromLandscape( UTexture2D& Heightmap )
{
	UWorld* pWorld = GEditor->GetEditorWorldContext().World();
	assert( pWorld );

	TArray<AActor*> LandscapeActors;
	UGameplayStatics::GetAllActorsOfClass( pWorld, ALandscape::StaticClass(), LandscapeActors );
	assert( LandscapeActors.Num() == 1 );

	ALandscape* pLandscapeActor = Cast<ALandscape>( LandscapeActors[ 0 ] );
	const FTransform& LandscapeActorTransform = pLandscapeActor->GetTransform();

	_HeightMapRT->InitCustomFormat( gHeightmapSizeX, gHeightmapSizeY, EPixelFormat::PF_G16, false );

	pLandscapeActor->RenderHeightmap( FTransform::Identity, {}, _HeightMapRT );

	_HeightMapRT->UpdateTexture( &Heightmap );
}

Trying to read the texture data into memory. Trigger on clicking the “Read Heightmap” button.

void FHeightmapToolModule::CopyHeightmapData()
{
	UTexture2D& Heightmap = *_Heightmap;

	struct FCopyBufferData {
		UTexture2D* Texture;
		TPromise<void> Promise;
		TArray<FColor> DestBuffer;
	};
	using FCommandDataPtr = TSharedPtr<FCopyBufferData, ESPMode::ThreadSafe>;
	FCommandDataPtr CommandData = MakeShared<FCopyBufferData, ESPMode::ThreadSafe>();
	CommandData->Texture = &Heightmap;
	CommandData->DestBuffer.SetNum( Heightmap.GetSizeX() * Heightmap.GetSizeY() );

	{
		ENQUEUE_RENDER_COMMAND( ReadHeightmapTexture )(
			[CommandData]( FRHICommandListImmediate& RHICmdList )
			{
				auto Texture2DRHI = CommandData->Texture->GetResource()->GetTexture2DRHI();
				uint32 DestPitch{ 0 };
				void* MappedTextureMemory = RHILockTexture2D( Texture2DRHI, 0, EResourceLockMode::RLM_ReadOnly, DestPitch, false );

				uint32 SizeX = CommandData->Texture->GetSizeX();
				uint32 SizeY = CommandData->Texture->GetSizeY();

				FMemory::Memcpy( CommandData->DestBuffer.GetData(), MappedTextureMemory, SizeX * SizeY * sizeof( FColor ) );

				RHIUnlockTexture2D( Texture2DRHI, 0, false );
				// signal completion of the operation
				CommandData->Promise.SetValue();
			} );

		CommandData->Promise.GetFuture().Get();
	}
}

It crashes on the memcpy() when trying to access the texture memory. Anyone got any clues why? The destination buffer is sized correctly.