Path: utzoo!attcan!uunet!husc6!purdue!decwrl!asente
From: asente@decwrl.dec.com (Paul Asente)
Newsgroups: comp.windows.x
Subject: Re: accelerators
Message-ID: <901@bacchus.dec.com>
Date: 14 Nov 88 22:28:40 GMT
References: <861@fxgrp.UUCP>
Organization: DEC Western Software Lab
Lines: 65

In article <861@fxgrp.UUCP> grady@fxgrp (Steven Grady) writes:
>This accelerator can be used after it has been installed in
>other widgets, using XtInstallAccelerators().  The destination
>widget, after this call, will have all the mappings of the
>accelerators of the source widget available.  Thus, if I
>say "XtInstallAccelerators(textEditingWidget, menuWidget)",
>then all my accelerators for the menu widget will now be available
>from within the context of the text-editing widget.
>
>Do I have it right so far?

So far, so good.

>OK, assuming I do..  What does it mean to "display" an accelerator?
>Why would a widget want to display its accelerators?
>What exactly does the display_accelerator function do?

Often times a widget will want to display in itself some representation of
the accelerator.  For example, if you have a menu item accessible through
the ^C accelerator, you might want to display the string "^C" in your menu
item.  The display_accelerator function gets called when a widget's
accelerator is installed, and gets passed a text representation of the
accelerator.  It can do anything it wants with it, including ignoring it.

>There is a variable used by some programs, XtInheritDisplayAccelerator,
>which is mentioned in the Xt doc, but not described.
>This variable is the only reference to accelerators I've found
>in _any_ of the X11 code.  Makes it hard to learn by looking
>at examples..  Does anyone actually use accelerators?

The built-in widgets (Core, Composite...) are basically prototypes; they
normally have no actions, and thus, no accelerators.  Displaying
accelerators is meaningless for them, so they have NULL
display_accelerator functions.  XtInheritDisplayAccelerator, like other
XtInherit values, specifies that a widget should inherit its parent's
display_accelerator function.

>My other concern is the design of accelerators in general.
>My thought is that it would be better to allow have widgets
>make public (within the application) those functions that
>can be associated with accelerators.  Then, any widget which
>wants to use an accelerator can bind to that action in a way
>similar to other translations, ie:
>	program*textEditingWidget.translations: #override\
>		<Ctrl>X: program*menuWidget*itemX()

What you specify for the toolkit is
	program*menuWidget.accelerator: <Ctrl>X:itemX()
and install the accelerator for menuWidget in some other widget (e.g.
textEditingWidget) in your code.

>This would allow different widgets to use different accelerators
>to access a function -- for instance, one widget could use
>"<Key>?" to pop up a help widget, whereas another could use
>"<Ctrl>H".  To make an accelerator available to all widgets,
>you could simply say:
>	program*translations: #augment\
>		<Ctrl>X: program*menuWidget*itemX()

One design aim was that a particular widget instance should always have
the same accelerator anywhere it is available -- you don't want people to
type one accelerator sequence one place and another one someplace else.
You may disagree with this, but it seems a laudible goal.

	-paul asente