window-size-change-functions

window-size-change-functions is a variable defined in `C source code'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
Functions called before redisplay, if window sizes have changed.
The value should be a list of functions that take one argument.
Just before redisplay, for each frame, if any of its windows have changed
size since the last redisplay, or have been split or deleted,
all the functions in the list are called, with the frame as argument.