mouse-position-function

mouse-position-function 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:
If non-nil, function to transform normal value of `mouse-position'.
`mouse-position' and `mouse-pixel-position' call this function, passing their
usual return value as argument, and return whatever this function returns.
This abnormal hook exists for the benefit of packages like `xt-mouse.el'
which need to do mouse handling at the Lisp level.