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30. Gutter

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

30.1 Gutter Intro  An introduction.
30.2 Creating Gutters  How to create a gutter.
30.3 Specifying a Gutter  Setting a gutter's contents.
30.4 Other Gutter Variables  Controlling the size of gutters.
30.5 Common Gutter Widgets  Things to put in gutters.


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30.1 Gutter Intro

A 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 (see section 48. 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 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 set-default-gutter-position. The way this works is that 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.


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30.2 Creating Gutters

Function: make-gutter-specifier spec-list

Return a new gutter specifier object with the given specification list. 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. See section 48. Specifiers, for more information about specifiers.

Gutter specifiers are used to specify the format of a gutter. The values of the variables default-gutter, top-gutter, left-gutter, right-gutter, and 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 nil. If 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 `gutter-visible' variable, and displayed according to any text properties they contain.

Function: make-gutter-size-specifier spec-list

Return a new gutter-size specifier object with the given spec list. 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. See section 48. 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," i.e., height for top and bottom gutters and width for left and right gutters. The values of the variables default-gutter-size, top-gutter-size, left-gutter-size, right-gutter-size, and bottom-gutter-size are always gutter-size specifiers.

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

Function: make-gutter-visible-specifier spec-list

Return a new gutter-visible specifier object with the given spec list. 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. See section 48. Specifiers, for more information about specifiers.

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

Valid gutter-visible instantiators are t, 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.


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30.3 Specifying a Gutter

In order to specify the contents of a gutter, set one of the specifier variables default-gutter, top-gutter, bottom-gutter, left-gutter, or right-gutter. These are specifiers, which means you set them with set-specifier and query them with specifier-specs or specifier-instance. You will get an error if you try to set them using setq. The valid instantiators for these specifiers are gutter descriptors, as described above. See section 48. Specifiers, for more information.

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

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

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 top-gutter-height, bottom-gutter-height, left-gutter-width, and right-gutter-width, and the visibility status is controlled by the specifiers top-gutter-visible-p, bottom-gutter-visible-p, left-gutter-visible-p, and right-gutter-visible-p (see section 30.4 Other Gutter Variables).

Function: set-default-gutter-position position
This function sets the position that the default-gutter will be displayed at. Valid positions are the symbols top, bottom, left and right. What this actually does is set the fallback specifier for the position-specific specifier corresponding to the given position to default-gutter, and set the fallbacks for the other position-specific specifiers to nil. It also does the same thing for the position-specific thickness and visibility specifiers, which inherit from one of default-gutter-height or default-gutter-width, and from default-gutter-visible-p, respectively (see section 30.4 Other Gutter Variables).

Function: default-gutter-position
This function returns the position that the default-gutter will be displayed at.

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 default-gutter is consulted if default-gutter-position indicates this position.

Specifier: top-gutter
Specifier for the gutter at the top of the frame.

Specifier: bottom-gutter
Specifier for the gutter at the bottom of the frame.

Specifier: left-gutter
Specifier for the gutter at the left edge of the frame.

Specifier: right-gutter
Specifier for the gutter at the right edge of the frame.

Function: gutter-specifier-p object
This function returns non-nil if 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.


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30.4 Other Gutter Variables

The variables to control the gutter thickness, visibility status, and captioned status are all specifiers. See section 48. Specifiers.

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 set-default-gutter-position. If the corresponding position-specific gutter thickness specifier (e.g. top-gutter-height if default-gutter-position is top) does not specify a thickness in a particular domain (a window or a frame), then the value of default-gutter-height or default-gutter-width (depending on the gutter orientation) in that domain, if any, will be used instead.

Specifier: default-gutter-width
This specifies the width of the default gutter, if it's oriented vertically. This behaves like default-gutter-height.

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

Specifier: top-gutter-height
This specifies the height of the top gutter.

Specifier: bottom-gutter-height
This specifies the height of the bottom gutter.

Specifier: left-gutter-width
This specifies the width of the left gutter.

Specifier: right-gutter-width
This specifies the width of the right gutter.

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.

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

Specifier: top-gutter-visible-p
This specifies whether the top gutter is visible.

Specifier: bottom-gutter-visible-p
This specifies whether the bottom gutter is visible.

Specifier: left-gutter-visible-p
This specifies whether the left gutter is visible.

Specifier: right-gutter-visible-p
This specifies whether the right gutter is visible.

default-gutter-visible-p and all of the position-specific gutter visibility specifiers have a fallback value of 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 nil value specified for 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.


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30.5 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.

These widgets are currently documented only in the library `gutter-items'.

30.5.1 Buffer Tabs  Tabbed divider index metaphor for switching buffers.
30.5.2 Progress Bars  Visual indication of operation progress.


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30.5.1 Buffer Tabs

Not documented yet.


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30.5.2 Progress Bars

Not documented yet.


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