AiFollow: add a threshold when turning to target

[akortunov]

Fixes bug #3749.

Note: in current implementation followers turn faster than in Morrowind. Is there any way to fix it?

[ghost]

We will get NaN here if direction is zero (actor and target in the same position)

[akortunov]

Yes, I got It.
But we have the same code in AiWander, AiFace and pathfinding.cpp (I just took already existing formula).
Should we change these files too?

[akortunov]

Also, IIRC, std::atan2(0, 0) == 0 (atan2 should return NaN only if dir.x() is NaN or dir.y() is NaN).

[ghost]

Note: in current implementation followers turn faster than in Morrowind. Is there any way to fix it?

Don't we have a speed argument to zTurn? Or do you mean there is a delay before they start turning at all?

Is there any reason we can't use the threshold function built in to zTurn ('epsilonRadians') ?

[akortunov]

I mean angular velocity.
Just run in circles around any follower in vanilla game and OpenMW.
Maybe I'm wrong, but looks like in OpenMW followers have higher angular velocity.

Don't we have a speed argument to zTurn?

I tried to use it, but without success. Even with very small values there is no noticeable difference.

[ghost]

Don't we have a speed argument to zTurn?

I tried to use it, but without success. Even with very small values there is no noticeable difference

Then we should probably find out what's wrong with it, rather than adding a new method on top.

What about this one? "Is there any reason we can't use the threshold function built in to zTurn ('epsilonRadians') ?"

[akortunov]

I rewrote this PR to use epsilonRadians.

Notes:

1. I did not change pathTo() function because we need a threshold only in AiFollow.
2. Looks like followers in Morrowind turn around without playing animation. I am not sure if we want to replicate this behaviour.