Re: Emacs-devel Digest, Vol 131, Issue 82

[Eli Zaretskii <eliz@gnu.org>]

> From: David Requena Zabala <DRequena@gamalquiler.com>
> Date: Tue, 20 Jan 2015 10:23:37 +0100
> 
> At any rate, if someone was to implement an hypothetical 
> '--without-w32-toolkit-scroll-bars', would it take entering much into the elisp 
> realm?

No, it shouldn't touch the Lisp level at all.  The implementation of
the scroll bars is entirely on the C level.

> Probably having different kinds of sc means some form of common scroll bar api
> exists for sc implementation code to use and/or plug in. I mean, kind of how 
> the w32_wnd_proc callback handles the WM_EMACS_CREATESCROLLBAR message by 
> calling w32_createscrollbar. Is this the case? Is it described somewhere?

See w32term.c:w32_set_vertical_scroll_bar for the Windows
implementation and xterm.c:XTset_vertical_scroll_bar for the X
implementation.  The guts are in x_scroll_bar_create in both cases,
but the API you were asking about is defined by the former two
functions, which implement the hook called by Emacs when it wants to
display the scroll bar.  How this maps into the windowing system is
entirely hidden from the higher levels; on Windows this sends a
message to the GUI thread, which calls the corresponding Windows API.