Make the trace line persistent

[Xiaocheng Song (songxiaocheng)]

It is supposed to press "T" to toggle a persistent trace line but it is just shown as a little tail behind the drone. This commit fixes this problem.

[Ratnesh Madaan (madratman)]

thanks for this.
I think it would be nice to have a call to FlushPersistentDebugLines as well, perhaps with another key, to clear the debug lines on demand https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Source/Runtime/Engine/Public/DrawDebugHelpers.h#L18

[Xiaocheng Song (songxiaocheng)]

thanks for this.
I think it would be nice to have a call to FlushPersistentDebugLines as well, perhaps with another key, to clear the debug lines on demand https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Source/Runtime/Engine/Public/DrawDebugHelpers.h#L18

I believe this is already implemented in the previous version here where UKismetSystemLibrary::FlushPersistentDebugLines works well which did the same thing with FlushPersistentDebugLines. Just press "T" to toggle the trace line on and off.

The DrawDebugLine was replaced by UKismetSystemLibrary::DrawDebugLine in this commit but it seems the latter function lacks a bPersistentLines option which causes the problem I mentioned above.