Bisector orientation

[carlos_m_gil_p]

Hello guys, how have you been?
I wanted to see if you can help me with this.
I am trying to draw a line on the bisector between three points.
Int - First point I always select (Intersection)
P1 and P2 - They have no order when selecting them (Direction of angles)
The problem is that sometimes it is drawn correctly and other times in the opposite direction and I don't know how to guide how the new line is drawn.
I attach how I am doing it and I am also going to attach a dwg file so that you can understand me better.
Or I don't know if anyone already has a better routine.

(defun c:xxx (/ int p1 p2 direct) 
  (setq int (getpoint))
  (setq p1 (getpoint))
  (setq p2 (getpoint))
  (setq direct (polar int (/ (+ (angle int p1) (angle int p2)) 2.0) 20.0))
  (command "_.line" "_non" int "_non" direct "")
  (princ))

Thank you.

[Kent1Cooper]

You don't show what the wrong result looks like.  But I suspect the issue has to do with the 0° direction falling between the directions to the two points.  For example, if the direction from the intersection to one point is 45° and to the other is -45°, that second direction is really 315°, so the sum is 360°, meaning halfway between is 180°, not the 0° you want.

[carlos_m_gil_p]

Hello @Kent1Cooper how are you.
As always, thanks for your help.
I don't understand much about the angles, but anyway, I'm going to attach a dwg with the correct one and what's wrong when I apply the lisp, sorry for not doing it in the previous one.
Thank you.

[Kent1Cooper · Accepted solution]

As I suspected, the problem occurs when the two directions you want to split between straddle the 0° direction [dashed blue] from the intersection:

I think it might be valid to test whether the difference between the two angles is greater than 180°, and if so, reverse the angle argument in the (polar) function [i.e add pi radians to it].  From this:

(defun c:xxx (/ int p1 p2 direct)
  (setq
    int (getpoint)
    p1 (getpoint)
    p2 (getpoint)
    direct
      (polar
        int
        (+
          (/ (+ (angle int p1) (angle int p2)) 2.0)
          (if (> (abs (- (angle int p1) (angle int p2))) pi) pi 0)
        ); +
        20.0
      ); polar
  )
  (command "_.line" "_non" int "_non" direct "")
  (princ)
)

in your sample drawing, using your Polylines and Points, I got the yellow results here at those corners:

[I have not tested it any more than that.]

[carlos_m_gil_p]

Thank you very much brother, for me so far it works very well.
God bless you and fill you with patience to continue helping.
Greetings.