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31 Jul 2002 13:58:22 +0200
Gnus/5.09 (Gnus v5.9.0) Emacs/21.2
Richard Stallman <address@hidden> writes:
> IIRC, the scroll bar callback is invoked with action information only,
> Could you explain what "action information" means?
I meant "user action". In the Motif case, for example the scroll bar
callback in invoked for user action meaning "line down", "page up" etc.
> (I'm assuming you are the expert on this--wasn't it you who
> wrote that code? If I should ask someone else instead, please
> tell me who.)
I wouldn't call myself an expert on this stuff. Stefan, BTW, also
worked on the scroll bar code. He probably knows at least as much
about this as I do.
> See, for instance, the LessTif/Motif callback xm_scroll_callback in
> xterm.c. AFAIK, the callback cannot tell which user actions caused
> the action, i.e. up/down events etc.
> I see one "action" is XmCR_DRAG. Can you find out, and tell me,
> exactly when that is given?
The only info I have is a man page. I'll attach it at the end.
> Is it for the down event on the slider, or for an up event after
> sliding the slider, or what?
As I read the man page, XmCR_DRAG is received while the user is
dragging the slider for "each incremental change of position", so it
would be neither up nor down event.
> What does a callback with that code signify?
> I noticed that xm_scroll_callback calls x_send_scroll_bar_event:
> /* Send a client message with message type Xatom_Scrollbar for a
> scroll action to the frame of WINDOW. PART is a value identifying
> the part of the scroll bar that was clicked on. PORTION is the
> amount to scroll of a whole of WHOLE. */
> static void
> x_send_scroll_bar_event (window, part, portion, whole)
> I don't understand the role of this function in the overall
> implementation of toolkit scroll bars. Could you explain it?
> It seems to be sending some sort of X event to Emacs's X window.
> Why is that? What happens when that client message "arrives"
> again? Which part of the code in Emacs handles it then?
> And why not call it directly instead of sending a message
> to the X server?
I've used x_send_scroll_bar_event to "translate" the invocation of the
scroll bar callback to an X event that is handled in XTread_socket
like other events. This seemed to be the easiest way to orderly
produce a scroll bar input event in the kdb queue because I saw no way
to predict when the callback is called (asynchronously).
Description: XmScrollBar man page