make a sprite with only two pixels painted, hold ctrl and crop the sprite to maintain the size of 1x2 pixels.
Align the origin on the left side.
Call it as "Line".
Go to the events system and set the line behavior like this:
= On start of layout
-> Create Line in (Point01.X, Point01.Y)
-> Set Line width to [distance(Line.X, Line.Y, Point02.X, Point02.Y)]
-> Rotate Line to [angle(Line.X, Line.Y, Point02.X, Point02.Y)]
That's it...