Variable: pre-redisplay-function
pre-redisplay-function is a variable defined in xdisp.c.
Value
redisplay--pre-redisplay-functions
Documentation
Function run just before redisplay.
It is called with one argument, which is the set of windows that are to be redisplayed. This set can be nil (meaning, only the selected window), or t (meaning all windows).
Probably introduced at or before Emacs version 24.4.
Source Code
// Defined in /usr/src/emacs/src/xdisp.c
DEFVAR_LISP ("pre-redisplay-function", Vpre_redisplay_function,
doc: /* Function run just before redisplay.
It is called with one argument, which is the set of windows that are to
be redisplayed. This set can be nil (meaning, only the selected window),
or t (meaning all windows). */);