What does the FVector2D parameter to AddOnScreenDebugMessage do?

I am familiar with how to use UEngine::AddOnScreenDebugMessage, only the last parameter, FVector2D& TextScale doesn’t seem to do anything. Its default value is the 2D unit vector, but when I pass in something like

const FVector2D Scale = FVector2D(2.f, 2.f);
if (GEngine) GEngine->AddOnScreenDebugMessage(-1, 1.5f, FColor::White, TEXT("Bigger???"), true, Scale);

nothing is different than if I didn’t pass in that last parameter at all. What is this parameter and what does it do?


TextScale may only works with key != -1.