30.3 Gutter Descriptor Format

The contents of a gutter are specified using a gutter descriptor. The format of a gutter descriptor is a list of gutter button descriptors. Each gutter button descriptor is a vector in one of the following formats:

• [glyph-list function enabled-p help]
• [:style 2d-or-3d]
• [:style 2d-or-3d :size width-or-height]
• [:size width-or-height :style 2d-or-3d]

Optionally, one of the gutter button descriptors may be nil instead of a vector; this signifies the division between the gutter buttons that are to be displayed flush-left, and the buttons to be displayed flush-right.

The first vector format above specifies a normal gutter button; the others specify blank areas in the gutter.

For the first vector format:

• glyph-list should be a list of one to six glyphs (as created by make-glyph) or a symbol whose value is such a list. The first glyph, which must be provided, is the glyph used to display the gutter button when it is in the “up” (not pressed) state. The optional second glyph is for displaying the button when it is in the “down” (pressed) state. The optional third glyph is for when the button is disabled. The last three glyphs are for displaying the button in the “up”, “down”, and “disabled” states, respectively, but are used when the user has called for captioned gutter buttons (using gutter-buttons-captioned-p). The function gutter-make-button-list is useful in creating these glyph lists.
• Even if you do not provide separate down-state and disabled-state glyphs, the user will still get visual feedback to indicate which state the button is in. Buttons in the up-state are displayed with a shadowed border that gives a raised appearance to the button. Buttons in the down-state are displayed with shadows that give a recessed appearance. Buttons in the disabled state are displayed with no shadows, giving a 2-d effect.
• If some of the gutter glyphs are not provided, they inherit as follows:

       UP:                up
       DOWN:              down -> up
       DISABLED:          disabled -> up
       CAP-UP:            cap-up -> up
       CAP-DOWN:          cap-down -> cap-up -> down -> up
       CAP-DISABLED:      cap-disabled -> cap-up -> disabled -> up
  

• The second element function is a function to be called when the gutter button is activated (i.e. when the mouse is released over the gutter button, if the press occurred in the gutter). It can be any form accepted by call-interactively, since this is how it is invoked.
• The third element enabled-p specifies whether the gutter button is enabled (disabled buttons do nothing when they are activated, and are displayed differently; see above). It should be either a boolean or a form that evaluates to a boolean.
• The fourth element help, if non-nil, should be a string. This string is displayed in the echo area when the mouse passes over the gutter button.

For the other vector formats (specifying blank areas of the gutter):

• 2d-or-3d should be one of the symbols 2d or 3d, indicating whether the area is displayed with shadows (giving it a raised, 3-d appearance) or without shadows (giving it a flat appearance).
• width-or-height specifies the length, in pixels, of the blank area. If omitted, it defaults to a device-specific value (8 pixels for X devices).

Function: gutter-make-button-list up &optional down disabled cap-up cap-down cap-disabled

This function calls make-glyph on each arg and returns a list of the results. This is useful for setting the first argument of a gutter button descriptor (typically, the result of this function is assigned to a symbol, which is specified as the first argument of the gutter button descriptor).

Function: check-gutter-button-syntax button &optional noerror

Verify the syntax of entry button in a gutter description list. If you want to verify the syntax of a gutter description list as a whole, use check-valid-instantiator with a specifier type of gutter.