Re: "after" variable watchers

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Eli Zaretskii <eliz@gnu.org>, npostavs@gmail.com, emacs-devel@gnu.org
> From: martin rudalics <rudalics@gmx.at>
> Date: Tue, 18 May 2021 19:01:34 +0200
> 
>  > What was the problem you encountered when you tried to add:
>  >
>  >      if (<dirty>) window_updeco_window (...);
>  >
>  > to the getters of the realized values?
> 
> There are too many implicit "realized" values to make this work nicely.
> Think of macros like WINDOW_BODY_PIXEL_WIDTH, WINDOW_BOX_LEFT_EDGE_X,
> WINDOW_BOX_RIGHT_EDGE_X, WINDOW_SCROLL_BAR_X or functions like
> window_box_height in addition to the things window_updeco_window sets
> directly.

I don't think I understand this reasoning.  Changes in these values
are only visible as result of the next redisplay cycle, no?  So in
effect these values "wait" for the next redisplay anyway, right?

> Right.  But note that I implicitly call window_updeco_window also
> whenever I change a window's size, for example, from adjust_frame_size
> after a frame got resized.

I think Stefan asks why do we need to do that.  Why not wait for when
these values are needed by redisplay, and calculate them only then?