Hacky way to see if the cursor is over a UI element. Useful for detecting whether to do raycasts into the world or not.

IsOverUIElement.h

static const FString RootName = "SGameLayerManager";

bool IsOverUIElement()
{
	FVector2D CursorPos = FSlateApplication::Get().GetCursorPos();
	FWidgetPath WidgetPath = FSlateApplication::Get().LocateWindowUnderMouse( CursorPos, FSlateApplication::Get().GetInteractiveTopLevelWindows() );

	if ( WidgetPath.IsValid() )
	{
		const FArrangedChildren::FArrangedWidgetArray& AllArrangedWidgets = WidgetPath.Widgets.GetInternalArray();
		bool FoundRoot = false;
		for ( int32 i = 0; i < WidgetPath.Widgets.Num(); ++i )
		{
			FArrangedWidget& ArrangedWidget = WidgetPath.Widgets[ i ];
			TSharedRef<SWidget> Widget = ArrangedWidget.Widget;
			if ( Widget->GetTypeAsString() == RootName )
			{
				// Wait until the next child to return to see if we're over something inside the root
				FoundRoot = true;
			}
			else if ( FoundRoot )
			{
				return true;
			}
		}
	}
	return false;
}