@c -*-texinfo-*-
@c This is part of the XEmacs Lisp Reference Manual.
@c Copyright (C) 1994, 1995 Ben Wing.
@c Copyright (C) 1999 Andy Piper.
@c Copyright (C) 1999 Stephen J. Turnbull.
@c See the file lispref.texi for copying conditions.
@setfilename ../../info/gutter.info
@node Gutter, Scrollbars, Toolbar, top
@chapter Gutter
@cindex gutter

  A gutter is a rectangle displayed along one edge of a frame.  It
can contain arbitrary text or graphics.

@menu
* Gutter Intro::		An introduction.
* Creating Gutters::            How to create a gutter.
* Specifying a Gutter::		Setting a gutter's contents.
* Other Gutter Variables::	Controlling the size of gutters.
* Common Gutter Widgets::       Things to put in gutters.
@end menu

@node Gutter Intro, Creating Gutters, Gutter, Gutter
@section Gutter Intro

  A @dfn{gutter} is a rectangle displayed along one edge of a frame.  It
can contain arbitrary text or graphics.  It could be considered a
generalization of a toolbar, although toolbars are not currently
implemented using gutters.

  In XEmacs, a gutter can be displayed along any of the four edges
of the frame, and two or more different edges can be displaying
gutters simultaneously.  The contents, thickness, and visibility of
the gutters can be controlled separately, and the values can
be per-buffer, per-frame, etc., using specifiers (@pxref{Specifiers}).

  Normally, there is one gutter displayed in a frame.  Usually, this is
the default gutter, containing buffer tabs, but modes can override this
and substitute their own gutter.  This default gutter is usually
positioned along the top of the frame, but this can be changed using
@code{set-default-gutter-position}.

  Note that, for each of the gutter properties (contents, thickness,
and visibility), there is a separate specifier for each of the four
gutter positions (top, bottom, left, and right), and an additional
specifier for the ``default'' gutter, i.e. the gutter whose
position is controlled by @code{set-default-gutter-position}.  The
way this works is that @code{set-default-gutter-position} arranges
things so that the appropriate position-specific specifiers for the
default position inherit from the corresponding default specifiers.
That way, if the position-specific specifier does not give a value
(which it usually doesn't), then the value from the default
specifier applies.  If you want to control the default gutter, you
just change the default specifiers, and everything works.  A package
such as VM that wants to put its own gutter in a different location
from the default just sets the position-specific specifiers, and if
the user sets the default gutter to the same position, it will just
not be visible.

@node Creating Gutters, Specifying a Gutter, Gutter Intro, Gutter
@section Creating Gutters

@defun make-gutter-specifier spec-list

Return a new @code{gutter} specifier object with the given specification
list.  @var{spec-list} can be a list of specifications (each of which is
a cons of a locale and a list of instantiators), a single instantiator,
or a list of instantiators.  @xref{Specifiers}, for more information
about specifiers.

Gutter specifiers are used to specify the format of a gutter.  The
values of the variables @code{default-gutter}, @code{top-gutter},
@code{left-gutter}, @code{right-gutter}, and @code{bottom-gutter} are
always gutter specifiers.

Valid gutter instantiators are called ``gutter descriptors.''  A gutter
descriptor may be a string, a property-list with symbol keys and string
values, or @code{nil}.  If @code{nil}, nothing will be displayed in the
gutter.  If a string, the string will be displayed, with text properties
such as faces and additional glyphs taken from the extents in the
string, if any.  If a property-list of strings, the string values will
be conditionally concatenated according to the contents of the
corresponding @samp{gutter-visible} variable, and displayed according to
any text properties they contain.
@end defun

@defun make-gutter-size-specifier spec-list

Return a new @code{gutter-size} specifier object with the given spec
list.  @var{spec-list} can be a list of specifications (each of which is
a cons of a locale and a list of instantiators), a single instantiator,
or a list of instantiators.  @xref{Specifiers}, for more information
about specifiers.

Gutter-size specifiers are used to specify the size of a gutter.
The width of top and bottom gutters and the height of left and right
gutters are always adjusted to the size of the frame, so ``size'' means
``thickness,'' @emph{i.e.}, height for top and bottom gutters and width
for left and right gutters.  The values of the variables
@code{default-gutter-size}, @code{top-gutter-size},
@code{left-gutter-size}, @code{right-gutter-size}, and
@code{bottom-gutter-size} are always gutter-size specifiers.

Valid gutter-size instantiators are either integers or the special
symbol @code{autodetect}.  If a gutter-size is set to @code{autodetect}
them the size of the gutter will be adjusted to just accommodate the
gutter's contents.  @code{autodetect} only works for top and bottom
gutters.
@end defun

@defun make-gutter-visible-specifier spec-list

Return a new @code{gutter-visible} specifier object with the given spec
list.  @var{spec-list} can be a list of specifications (each of which is
a cons of a locale and a list of instantiators), a single instantiator,
or a list of instantiators.  @xref{Specifiers}, for more information
about specifiers.

Gutter-visible specifiers are used to specify the visibility of a
gutter.  The values of the variables @code{default-gutter-visible-p},
@code{top-gutter-visible-p}, @code{left-gutter-visible-p},
@code{right-gutter-visible-p}, and @code{bottom-gutter-visible-p} are
always gutter-visible specifiers.

Valid gutter-visible instantiators are @code{t}, @code{nil} or a list of
symbols.  If a gutter-visible instantiator is set to a list of symbols,
and the corresponding gutter specification is a property-list of strings,
then property values of the gutter specification will only be visible if the
corresponding key occurs in the gutter-visible instantiator.
@end defun

@node Specifying a Gutter, Other Gutter Variables, Creating Gutters, Gutter
@section Specifying a Gutter

  In order to specify the contents of a gutter, set one of the specifier
variables @code{default-gutter}, @code{top-gutter},
@code{bottom-gutter}, @code{left-gutter}, or @code{right-gutter}.
These are specifiers, which means you set them with @code{set-specifier}
and query them with @code{specifier-specs} or @code{specifier-instance}.
You will get an error if you try to set them using @code{setq}.  The
valid instantiators for these specifiers are gutter descriptors, as
described above.  @xref{Specifiers}, for more information.

  Most of the time, you will set @code{default-gutter}, which allows
the user to choose where the gutter should go.

@defvr Specifier default-gutter
The position of this gutter is specified in the function
@code{default-gutter-position}.  If the corresponding
position-specific gutter (e.g. @code{top-gutter} if
@code{default-gutter-position} is @code{top}) does not specify a
gutter in a particular domain, then the value of @code{default-gutter}
in that domain, of any, will be used instead.
@end defvr

  Note that the gutter at any particular position will not be displayed
unless its thickness (width or height, depending on orientation) is
non-zero and its visibility status is true.  The thickness is controlled
by the specifiers @code{top-gutter-height},
@code{bottom-gutter-height}, @code{left-gutter-width}, and
@code{right-gutter-width}, and the visibility status is controlled by
the specifiers @code{top-gutter-visible-p},
@code{bottom-gutter-visible-p}, @code{left-gutter-visible-p}, and
@code{right-gutter-visible-p} (@pxref{Other Gutter Variables}).

@defun set-default-gutter-position position
This function sets the position that the @code{default-gutter} will be
displayed at.  Valid positions are the symbols @code{top},
@code{bottom}, @code{left} and @code{right}.  What this actually does is
set the fallback specifier for the position-specific specifier
corresponding to the given position to @code{default-gutter}, and set
the fallbacks for the other position-specific specifiers to @code{nil}.
It also does the same thing for the position-specific thickness and
visibility specifiers, which inherit from one of
@code{default-gutter-height} or @code{default-gutter-width}, and from
@code{default-gutter-visible-p}, respectively (@pxref{Other Gutter
Variables}).
@end defun

@defun default-gutter-position
This function returns the position that the @code{default-gutter} will
be displayed at.
@end defun

  You can also explicitly set a gutter at a particular position.  When
redisplay determines what to display at a particular position in a
particular domain (i.e. window), it first consults the position-specific
gutter.  If that does not yield a gutter descriptor, the
@code{default-gutter} is consulted if @code{default-gutter-position}
indicates this position.

@defvr Specifier top-gutter
Specifier for the gutter at the top of the frame.
@end defvr

@defvr Specifier bottom-gutter
Specifier for the gutter at the bottom of the frame.
@end defvr

@defvr Specifier left-gutter
Specifier for the gutter at the left edge of the frame.
@end defvr

@defvr Specifier right-gutter
Specifier for the gutter at the right edge of the frame.
@end defvr

@defun gutter-specifier-p object
This function returns non-@code{nil} if @var{object} is a gutter specifier.
Gutter specifiers are the actual objects contained in the gutter
variables described above, and their valid instantiators are
gutter descriptors.
@end defun

@node Other Gutter Variables, Common Gutter Widgets, Specifying a Gutter, Gutter
@section Other Gutter Variables

  The variables to control the gutter thickness, visibility status, and
captioned status are all specifiers.  @xref{Specifiers}.

@defvr Specifier default-gutter-height
This specifies the height of the default gutter, if it's oriented
horizontally.  The position of the default gutter is specified by the
function @code{set-default-gutter-position}.  If the corresponding
position-specific gutter thickness specifier
(e.g. @code{top-gutter-height} if @code{default-gutter-position} is
@code{top}) does not specify a thickness in a particular domain (a
window or a frame), then the value of @code{default-gutter-height} or
@code{default-gutter-width} (depending on the gutter orientation) in
that domain, if any, will be used instead.
@end defvr

@defvr Specifier default-gutter-width
This specifies the width of the default gutter, if it's oriented
vertically.  This behaves like @code{default-gutter-height}.
@end defvr

  Note that @code{default-gutter-height} is only used when
@code{default-gutter-position} is @code{top} or @code{bottom}, and
@code{default-gutter-width} is only used when
@code{default-gutter-position} is @code{left} or @code{right}.

@defvr Specifier top-gutter-height
This specifies the height of the top gutter.
@end defvr

@defvr Specifier bottom-gutter-height
This specifies the height of the bottom gutter.
@end defvr

@defvr Specifier left-gutter-width
This specifies the width of the left gutter.
@end defvr

@defvr Specifier right-gutter-width
This specifies the width of the right gutter.
@end defvr

  Note that all of the position-specific gutter thickness specifiers
have a fallback value of zero when they do not correspond to the
default gutter.  Therefore, you will have to set a non-zero thickness
value if you want a position-specific gutter to be displayed.

@defvr Specifier default-gutter-visible-p
This specifies whether the default gutter is visible.  The position of
the default gutter is specified by the function
@code{set-default-gutter-position}.  If the corresponding position-specific
gutter visibility specifier (e.g. @code{top-gutter-visible-p} if
@code{default-gutter-position} is @code{top}) does not specify a
visible-p value in a particular domain (a window or a frame), then the
value of @code{default-gutter-visible-p} in that domain, if any, will
be used instead.
@end defvr

@defvr Specifier top-gutter-visible-p
This specifies whether the top gutter is visible.
@end defvr

@defvr Specifier bottom-gutter-visible-p
This specifies whether the bottom gutter is visible.
@end defvr

@defvr Specifier left-gutter-visible-p
This specifies whether the left gutter is visible.
@end defvr

@defvr Specifier right-gutter-visible-p
This specifies whether the right gutter is visible.
@end defvr

@code{default-gutter-visible-p} and all of the position-specific
gutter visibility specifiers have a fallback value of true.

@c #### is this true?
  Internally, gutter thickness and visibility specifiers are instantiated
in both window and frame domains, for different purposes.  The value in
the domain of a frame's selected window specifies the actual gutter
thickness or visibility that you will see in that frame.  The value in
the domain of a frame itself specifies the gutter thickness or
visibility that is used in frame geometry calculations.

  Thus, for example, if you set the frame width to 80 characters and the
left gutter width for that frame to 68 pixels, then the frame will be
sized to fit 80 characters plus a 68-pixel left gutter.  If you then
set the left gutter width to 0 for a particular buffer (or if that
buffer does not specify a left gutter or has a @code{nil} value specified for
@code{left-gutter-visible-p}), you will find that, when that buffer is
displayed in the selected window, the window will have a width of 86 or
87 characters -- the frame is sized for a 68-pixel left gutter but the
selected window specifies that the left gutter is not visible, so it is
expanded to take up the slack.

@node Common Gutter Widgets, , Other Gutter Variables, Gutter
@section Common Gutter Widgets

  A gutter can contain arbitrary text.  So, for example, in an Info
buffer you could put the title of the current node in the top gutter,
and it would not scroll out of view in a long node.  (This is an
artificial example, since usually the node name is sufficiently
descriptive, and Info puts that in the mode line.)

  A more common use for the gutter is to hold some kind of active
widget.  The buffer-tab facility, available in all XEmacs frames,
creates an array of file-folder-like tabs, which the user can click with
the mouse to switch buffers.  W3 and font-lock use progress-bar widgets in the
bottom gutter to give a visual indication of the progress of
time-consuming operations like downloading and syntax highlighting.

@c #### Remove the following sentence when the subnodes are created.
These widgets are currently documented only in the library
@file{gutter-items}.

@menu
* Buffer Tabs::         Tabbed divider index metaphor for switching buffers.
* Progress Bars::       Visual indication of operation progress.
@end menu


@node Buffer Tabs, Progress Bars, ,Common Gutter Widgets
@subsection Buffer Tabs

  Not documented yet.


@node Progress Bars,  , Buffer Tabs, Common Gutter Widgets
@subsection Progress Bars

  Not documented yet.

