% -*- Mode: LaTeX; Package: CLIM-USER -*-
\chapter {Gadgets}
\label {gadgets}

\section {Overview of Gadgets}

\concept{Gadgets} are panes that implement such common toolkit components as
push buttons or scroll bars.  Each gadget class has a set of associated generic
functions that serve the same role that callbacks serve in traditional toolkits.
For example, a push button has an ``activate'' callback function that is invoked
when its button is ``pressed''; a scroll bar has a ``value changed'' callback
that is invoked after its indicator has been moved.

The gadget definitions specified by CLIM are abstract, in that the gadget
definition does not specify the exact user interface of the gadget, but only
specifies the semantics that the gadget should provide.  For instance, it is not
defined whether the user clicks on a push button with the mouse or moves the
mouse over the button and then presses some key on the keyboard to invoke the
``activate'' callback.  Each toolkit implementations will specify the ``look and
feel'' of their gadgets.  Typically, the look and feel will be derived directly
from the underlying toolkit.

Each of CLIM's abstract gadgets has at least one standard implementation that is
written using the facilities provided solely by CLIM itself.  The gadgets'
appearances are achieved via calls to the CLIM graphics functions, and their
interactive behavior is defined in terms of the CLIM input event processing
mechanism.  Since these gadget implementations are written entirely in terms of
CLIM, they are portable across all supported CLIM host window systems.
Furthermore, since the specific look and feel of each such gadget is ``fixed''
in CLIM Lisp code, the gadget implementation will look and behave the same in
all environments.


\section {Abstract Gadgets}

The push button and slider gadgets alluded to above are \concept{abstract
gadgets}.  The callback interface to all of the various implementations of the
gadget is defined by the abstract class.  In the \cl{:panes} clause of
\cl{define-application-frame}, the abbreviation for a gadget is the name of the
abstract gadget class.

At pane creation time (that is, \cl{make-pane}), the frame manager resolves the
abstract class into a specific implementation class; the implementation classes
specify the detailed look and feel of the gadget.  Each frame manager will keep
a mapping from abstract gadgets to an implementation class; if the frame manager
does not implement its own gadget for the abstract gadget classes in the
following sections, it should use the portable class provided by CLIM.  Since
every implementation of an abstract gadget class is a subclass of the abstract
class, they all share the same programmer interface.


\subsection {Using Gadgets}

Every gadget has a \concept{client} that is specified when the gadget is
created.  The client is notified via the callback mechanism when any important
user interaction takes place.   Typically, a gadget's client will be an
application frame or a composite pane.  Each callback generic function is
invoked on the gadget, its client, the gadget id (described below), and other
arguments that vary depending on the callback.

For example, the argument list for \cl{activate-callback} looks like
\arg{(gadget client gadget-id)}.  Assuming the programmer has defined an
application frame called \cl{button-test} that has a CLIM stream pane in the
slot \cl{output-pane}, he could write the following method:

\begin{verbatim}
(defmethod activate-callback
           ((button push-button) (client button-test) gadget-id) 
  (with-slots (output-pane) client
    (format output-pane "The button ~S was pressed, client ~S, id ~S."
       button client gadget-id)))
\end{verbatim}

One problem with this example is that it differentiates on the class of the
gadget, not on the particular gadget instance.  That is, the same method will
run for every push button that has the \cl{button-test} frame as its client.

One way to distinguish between the various gadgets is via the \concept{gadget
id}, which is also specified when the gadget is created.  The value of the
gadget id is passed as the third argument to each callback generic function.  In
this case, if we have two buttons, we might install \cl{start} and \cl{stop} as
the respective gadget ids and then use \cl{eql} specializers on the gadget ids.
We could then refine the above as:

\begin{verbatim}
(defmethod activate-callback
           ((button push-button) (client button-test) (gadget-id (eql 'start)))
  (start-test client))

(defmethod activate-callback
           ((button push-button) (client button-test) (gadget-id (eql 'stop)))
  (stop-test client))

;; Create the start and stop push buttons
(make-pane 'push-button
  :label "Start"
  :client frame :id 'start)
(make-pane 'push-button
  :label "Stop"
  :client frame :id 'stop)
\end{verbatim}

Another way to distinguish between gadgets is to explicitly specify what
function should be called when the callback is invoked.  This is specified when
the gadget is created by supplying an appropriate initarg.  The above example
could then be written as follows:

\begin{verbatim}
;; No callback methods needed, just create the push buttons
(make-pane 'push-button
  :label "Start"
  :client frame :id 'start
  :activate-callback
    #'(lambda (gadget)
        (start-test (gadget-client gadget))))
(make-pane 'push-button
  :label "Stop"
  :client frame :id 'stop
  :activate-callback
    #'(lambda (gadget)
        (stop-test (gadget-client gadget))))
\end{verbatim}


\subsection {Implementing Gadgets}

The following shows how a push button gadget might be implemented.

\begin{verbatim}
;; Here is a concrete implementation of a CLIM PUSH-BUTTON.
;; The "null" frame manager create a pane of type PUSH-BUTTON-PANE when
;; asked to create a PUSH-BUTTON.
(defclass push-button-pane
          (push-button
           leaf-pane
           space-requirement-mixin)
    ((show-as-default :initarg :show-as-default
                      :accessor push-button-show-as-default)
     (armed :initform nil)))

;; General highlight-by-inverting method.
(defmethod highlight-button ((pane push-button-pane) medium)
  (with-bounding-rectangle* (left top right bottom) (sheet-region pane)
    (draw-rectangle* medium left top right bottom
                     :ink +flipping-ink+ :filled t)
    (medium-force-output medium)))

;; Compute the amount of space required by a PUSH-BUTTON-PANE.
(defmethod compose-space ((pane push-button-pane) &key width height)
  (let ((x-margin 4)
        (y-margin 2))
  (multiple-value-bind (width height)
      (compute-gadget-label-size pane)
    (make-space-requirement :width  (+ width  (* x-margin 2))
                            :height (+ height (* y-margin 2))))

;; This gets invoked to draw the push button.
(defmethod handle-repaint ((pane push-button-pane) region)
  (declare (ignore region))
  (with-sheet-medium (medium pane)
    (let ((text (gadget-label pane))
          (text-style (slot-value pane 'text-style))
          (armed (slot-value pane 'armed))
          (region (sheet-region pane)))
      (multiple-value-call #'draw-rectangle*
        medium (bounding-rectangle* (sheet-region pane))
        :filled nil)
      (draw-text medium text (bounding-rectangle-center region)
                 :text-style text-style
                 :align-x ':center :align-y ':center)
      (when (eql armed ':button-press)
        (highlight-button pane medium)))))

(defmethod handle-event :around ((pane push-button-pane) (event pointer-event))
  (when (gadget-active-p pane)
    (call-next-method)))

;; When we enter the push button's region, arm it.  If there is a pointer
;; button down, make the button active as well.
(defmethod handle-event ((pane push-button-pane) (event pointer-enter-event))
  (with-slots (armed) pane
    (unless armed
      (cond ((let ((pointer (pointer-event-pointer event)))
               (and (pointer-button-state pointer)
                    (not (zerop (pointer-button-state pointer)))))
             (setf armed :active)
             (with-sheet-medium (medium pane)
               (highlight-button pane medium)))
            (t (setf armed t)))
      (armed-callback pane (gadget-client pane) (gadget-id pane)))))

;; When we leave the push button's region, disarm it.
(defmethod handle-event ((pane push-button-pane) (event pointer-exit-event))
  (with-slots (armed) pane
    (when armed
      (when (prog1 (eq armed :active) (setf armed nil))
        (with-sheet-medium (medium pane)
          (highlight-button pane medium)))
      (disarmed-callback pane (gadget-client pane) (gadget-id pane)))))

;; When the user presses a pointer button, ensure that the button
;; is armed, and highlight it. 
(defmethod handle-event ((pane push-button-pane) (event pointer-button-press-event))
  (with-slots (armed) pane
    (when armed
      (setf armed :active)
      (with-sheet-medium (medium pane)
        (highlight-button pane medium)))))

;; When the user releases the button and the button is still armed,
;; call the activate callback.
(defmethod handle-event ((pane push-button-pane) (event pointer-button-release-event))
  (with-slots (armed) pane
    (when (eq armed :active)
      (setf armed t)
      (with-sheet-medium (medium pane)
        (highlight-button pane medium))
      (activate-callback pane (gadget-client pane) (gadget-id pane)))))
\end{verbatim}


\section {Basic Gadget Classes}

The following are the basic gadget classes upon which all gadgets are built.

\Defprotoclass {gadget}

The protocol class that corresponds to a gadget, a subclass of \cl{pane}.
\IfYouWantClass {a} {gadget} {gadget}

All of the subclasses of \cl{gadget} are mutable.

\Defpredicate {gadgetp} {object}

Returns \term{true} if \arg{object} is a \term{gadget}, otherwise returns
\term{false}.

\Defclass {basic-gadget}

The basic class on which all CLIM gadgets are built, a subclass of \cl{gadget}.
\AbstractClass

\definitarg {:id}
\definitarg {:client}
\definitarg {:armed-callback}
\Definitarg {:disarmed-callback}

All subclasses of \cl{gadget} must handle these four initargs, which are used to
specify, respectively, the gadget id, client, armed callback, and disarmed
callback of the gadget.

\defgeneric {gadget-id} {gadget}
\Defgeneric {(setf gadget-id)} {id gadget}

Returns (or sets) the gadget id of the gadget \arg{gadget}.  The id is typically
a simple Lisp object that uniquely identifies the gadgets.

\defgeneric {gadget-client} {gadget}
\Defgeneric {(setf gadget-client)} {client gadget}

Returns the client of the gadget \arg{gadget}.  The client is often an
application frame, but it could be another gadget (for example, in the case of a
push button that is contained in a radio box, the client of the button could be
the radio box).

\defgeneric {gadget-armed-callback} {gadget}
\Defgeneric {gadget-disarmed-callback} {gadget}

Returns the functions that will be called when the armed or disarmed callback,
respectively, are invoked.  These functions will be invoked with a single
argument, the gadget.

When these functions return \cl{nil}, that indicates that there is no armed (or
disarmed) callback for the gadget.

\callback {armed-callback} {gadget client gadget-id}
\Callback {disarmed-callback} {gadget client gadget-id}

These callbacks are invoked when the gadget \arg{gadget} is, respectively, armed
or disarmed.

The exact definition of arming and disarming varies from gadget to gadget, but
typically a gadget becomes armed when the pointer is moved into its region, and
disarmed when the pointer moves out of its region.  A gadget will not call the
activate or value-changed callback unless it is armed.

The default methods (on \cl{basic-gadget}) call the function stored in
\cl{gadget-armed-callback} or \cl{gadget-disarmed-callback} with one argument,
the gadget.

\Defgeneric {activate-gadget} {gadget}

Causes the host gadget to become active, that is, available for input.

\Defgeneric {deactivate-gadget} {gadget}

Causes the host gadget to become inactive, that is, unavailable for input.  In
some environments this may cause the gadget to become grayed over; in others, no
visual effect may be detected.

\Defgeneric {gadget-active-p} {gadget}

Returns \cl{t} if the gadget \arg{gadget} is active (that is, has been activated
with \cl{activate-gadget}), otherwise returns \cl{nil}.

\Defgeneric {note-gadget-activated} {client gadget}

This function is invoked after a gadget is made active.  It is intended to allow
the client of the gadget to notice when the gadget has been activated.

\Defgeneric {note-gadget-deactivated} {client gadget}

This function is invoked after a gadget is made inactive.  It is intended to
allow the client of the gadget to notice when the gadget has been activated.
For instance, when the client is an application frame, the frame may invoke the
frame manager to ``gray out'' deactivated gadgets.


\Defclass {value-gadget}

The class used by gadgets that have a value; a subclass of \cl{basic-gadget}.
\AbstractClass

\definitarg {:value}
\Definitarg {:value-changed-callback}

All subclasses of \cl{value-gadget} must handle these two initargs, which are
used to specify, respectively, the initial value and the value changed callback
of the gadget.

\Defgeneric {gadget-value} {value-gadget}

Returns the value of the gadget \arg{value-gadget}.  The interpretation of the
value varies from gadget to gadget.  For example, a scroll bar's value might be
a number between 0 and 1, while a toggle button's value is either \cl{t} or
\cl{nil}.  (The documentation of each individual gadget below specifies how to
interpret the value.)

\Defgeneric {(setf gadget-value)} {value value-gadget \key invoke-callback}

Sets the gadget's value to the specified value.

If \arg{invoke-callback} is \term{true}, the value changed callback for the
gadget is invoked.  The default is \term{false}.  The syntax for using
\cl{(setf~gadget-value)} in conjunction with \arg{invoke-callback} is:

\begin{verbatim}
(setf (gadget-value gadget :invoke-callback t) new-value)
\end{verbatim}

\Defgeneric {gadget-value-changed-callback} {value-gadget}

Returns the function that will be called when the value changed callback is
invoked.  This function will be invoked with a two arguments, the gadget and
the new value.

When this function returns \cl{nil}, that indicates that there is no value
changed callback for the gadget.

\Callback {value-changed-callback} {value-gadget client gadget-id value}

This callback is invoked when the value of a gadget is changed, either by the
user or programatically.

The default method (on \cl{value-gadget}) calls the function stored in
\cl{gadget-value-changed-callback} with two arguments, the gadget and the new
value.

CLIM implementations must implement or inherit a method for
\cl{value-changed-callback} for every gadget that is a subclass of
\cl{value-gadget}.


\Defclass {action-gadget}

The class used by gadgets that perform some kind of action, such as a push
button; a subclass of \cl{basic-gadget}.
\AbstractClass

\Definitarg {:activate-callback}

All subclasses of \cl{action-gadget} must handle this initarg, which is used to
specify the activate callback of the gadget.

\Defgeneric {gadget-activate-callback} {action-gadget}

Returns the function that will be called when the gadget is activated.  This
function will be invoked with one argument, the gadget.

When this function returns \cl{nil}, that indicates that there is no value
activate callback for the gadget.

\Callback {activate-callback} {action-gadget client gadget-id}

This callback is invoked when the gadget is activated.

The default method (on \cl{action-gadget}) calls the function stored in
\cl{gadget-activate-callback} with one argument, the gadget.

CLIM implementations must implement or inherit a method for
\cl{activate-callback} for every gadget that is a subclass of
\cl{action-gadget}.


\Defclass {oriented-gadget-mixin}

The class that is mixed in to a gadget that has an orientation associated with
it, for example, a slider.  This class is not intended to be instantiated.

\Definitarg {:orientation}

All subclasses of \cl{oriented-gadget-mixin} must handle this initarg,
which is used to specify the orientation of the gadget.

\Defgeneric {gadget-orientation} {oriented-gadget}

Returns the orientation of the gadget \arg{oriented-gadget}.  Typically, this
will be a keyword such as \cl{:horizontal} or \cl{:vertical}.


\Defclass {labelled-gadget-mixin}

The class that is mixed in to a gadget that has a label, for example, a push
button.  This class is not intended to be instantiated.

\definitarg {:label}
\definitarg {:align-x}
\Definitarg {:align-y}

All subclasses of \cl{labelled-gadget-mixin} must handle these initargs, which
are used to specify the label, and its $x$ and $y$ alignment.  Labelled gadgets
will also have a text style for the label, but this is managed by the usual text
style mechanism for panes.

\defgeneric {gadget-label} {labelled-gadget}
\Defgeneric {(setf gadget-label)} {label labelled-gadget}

Returns (or sets) the label of the gadget \arg{labelled-gadget}.  The label must
be a string.  Changing the label of a gadget may result in invoking the layout
protocol on the gadget and its ancestor sheets.

\defgeneric {gadget-label-align-x} {labelled-gadget}
\defgeneric {(setf gadget-label-align-x)} {alignment labelled-gadget}
\defgeneric {gadget-label-align-y} {labelled-gadget}
\Defgeneric {(setf gadget-label-align-y)} {alignment labelled-gadget}

Returns (or sets) the alignment of the label of the gadget
\arg{labelled-gadget}.  Changing the alignment a gadget may result in invoking
the layout protocol on the gadget and its ancestor sheets.


\Defclass {range-gadget-mixin}

The class that is mixed in to a gadget that has a range, for example, a slider.
This class is not intended to be instantiated.

\definitarg {:min-value}
\Definitarg {:max-value}

All subclasses of \cl{range-gadget-mixin} must handle these two initargs, which
are used to specify the minimum and maximum value of the gadget.

\defgeneric {gadget-min-value} {range-gadget}
\Defgeneric {(setf gadget-min-value)} {min-value range-gadget}

Returns (or sets) the minimum value of the gadget \arg{range-gadget}.  It will be a real
number.

\defgeneric {gadget-max-value} {range-gadget}
\Defgeneric {(setf gadget-max-value)} {max-value range-gadget}

Returns (or sets) the maximum value of the gadget \arg{range-gadget}.  It will
be a real number.

\Defgeneric {gadget-range} {range-gadget}

Returns the range of \arg{range-gadget}, that is, the difference of the maximum value
and the minimum value.

\Defgeneric {gadget-range*} {range-gadget}

Returns the minimum and maximum values of \arg{range-gadget} as two values.


\section {Abstract Gadget Classes}

CLIM supplies a set of abstract gadgets that have been designed to be compatible
with with a variety of user interface toolkits, including Xt widget-based
toolkits (such as Motif), OpenLook, and MacApp and MicroSoft Windows.

CLIM's ``concrete'' gadget classes will all be subclasses of these abstract
gadget classes.  Each concrete gadget maps to an implementation-specific object
that is managed by the underlying toolkit.  For example, while a CLIM program
manipulates an object of class \cl{scroll-bar}, the underlying
implementation-specific object might be an Xt widget of type
\cl{Xm\_Scroll\_Bar}.  As events are processed on the underlying object the
corresponding generic operations are applied to the Lisp gadget.

\issue {ILA} {Do we want to define something like \cl{gadget-handle} that is a
documented way to get ahold of the underlying toolkit object?}

Note that not all operations will necessarily be generated by particular toolkit
implementations.  For example, a user interface toolkit that is designed for a
3-button mouse may generate significantly more gadget events than one designed
for a 1-button mouse.

%% Use \tt instead of \cl, such the hairy \cl macro will blow chow
\def\Gadget #1 {\subsection {The {\tt #1} Gadget}}


\Gadget {push-button}

The \cl{push-button} gadget provides press-to-activate switch behavior.

\cl{arm-callback} will be invoked when the push button becomes armed (such as
when the pointer moves into it, or a pointer button is pressed over it).  When
the button is actually activated (by releasing the pointer button over it),
\cl{activate-callback} will be invoked.  Finally, \cl{disarm-callback} will be
invoked after \cl{activate-callback}, or when the pointer is moved outside of
the button.

\Defclass {push-button}

The instantiable class that implements an abstract push button.  It is a
subclass of \cl{action-gadget} and \cl{labelled-gadget-mixin}.

\Definitarg {:show-as-default}

This is used to initialize the ``show as default'' property for the gadget,
described below.

\Defgeneric {push-button-show-as-default} {push-button}

Returns the ``show as default'' property for the push button gadget.  When
\term{true}, the push button will be drawn with a heavy border, which indicates
that this button is the ``default operation''.

\Defclass {push-button-pane}

The instantiable class that implements a portable push button; a subclass of
\cl{push-button}.


\Gadget {toggle-button}

The \cl{toggle-button} gadget provides ``on/off'' switch behavior.  This gadget
typically appears as a box that is optionally highlighted with a check-mark.  If
the check-mark is present, the gadget's value is \cl{t}, otherwise it is
\cl{nil}.

\cl{arm-callback} will be invoked when the toggle button becomes armed (such as
when the pointer moves into it, or a pointer button is pressed over it).  When
the toggle button is actually activated (by releasing the pointer button over
it), \cl{value-changed-callback} will be invoked.  Finally, \cl{disarm-callback}
will be invoked after \cl{value-changed-callback}, or when the pointer is moved
outside of the toggle button.

\Defclass {toggle-button}

The instantiable class that implements an abstract toggle button.  It is a
subclass of \cl{value-gadget} and \cl{labelled-gadget-mixin}.

\Definitarg {:indicator-type}

This is used to initialize the indicator type property for the gadget,
described below.

\Defgeneric {toggle-button-indicator-type} {toggle-button}

Returns the indicator type for the toggle button.  This will be either
\cl{:one-of} or \cl{:some-of}.  The indicator type controls the appearance of
the toggle button.  For example, many toolkits present a one-of-many choice
differently from a some-of-many choice.

\Defmethod {gadget-value} {(button \cl{toggle-button})}

Returns \term{true} if the button is selected, otherwise returns \term{false}.

\Defclass {toggle-button-pane}

The instantiable class that implements a portable toggle button; a subclass of
\cl{toggle-button}.


\Gadget {menu-button}

The \cl{menu-button} gadget provides similar behavior to the \cl{toggle-button}
gadget, except that it is intended for items in menus.  The returned value is
generally the item chosen from the menu.

\cl{arm-callback} will be invoked when the menu button becomes armed (such as
when the pointer moves into it, or a pointer button is pressed over it).  When
the menu button is actually activated (by releasing the pointer button over
it), \cl{value-changed-callback} will be invoked.  Finally, \cl{disarm-callback}
will be invoked after \cl{value-changed-callback}, or when the pointer is moved
outside of the menu button.

\Defclass {menu-button}

The instantiable class that implements an abstract menu button.  It is a
subclass of \cl{value-gadget} and \cl{labelled-gadget-mixin}.

\Defclass {menu-button-pane}

The instantiable class that implements a portable menu button; a subclass of
\cl{menu-button}.


\Gadget {scroll-bar}

The \cl{scroll-bar} gadget corresponds to a scroll bar.

\Defclass {scroll-bar}

The instantiable class that implements an abstract scroll bar.  This is a
subclass of \cl{value-gadget}, \cl{oriented-gadget-mixin}, and
\cl{range-gadget-mixin}.

\definitarg {:drag-callback}
\definitarg {:scroll-to-bottom-callback}
\definitarg {:scroll-to-top-callback}
\definitarg {:scroll-down-line-callback}
\definitarg {:scroll-up-line-callback}
\definitarg {:scroll-down-page-callback}
\Definitarg {:scroll-up-page-callback}

Specifies the drag and other scrolling callbacks for the scroll bar.

\Defgeneric {scroll-bar-drag-callback} {scroll-bar}

Returns the function that will be called when the indicator of the scroll bar is
dragged.  This function will be invoked with a two arguments, the scroll bar and
the new value.

\defgeneric {scroll-bar-scroll-to-bottom-callback} {scroll-bar}
\defgeneric {scroll-bar-scroll-to-top-callback} {scroll-bar}
\defgeneric {scroll-bar-scroll-down-line-callback} {scroll-bar}
\defgeneric {scroll-bar-scroll-up-line-callback} {scroll-bar}
\defgeneric {scroll-bar-scroll-down-page-callback} {scroll-bar}
\Defgeneric {scroll-bar-scroll-up-page-callback} {scroll-bar}

Returns the functions that will be used as callbacks when various parts of the
scroll bar are clicked on.  These are all functions of a single argument, the
scroll bar.

When any of these functions returns \cl{nil}, that indicates that there is no
callback of that type for the gadget.

\Callback {drag-callback} {scroll-bar client gadget-id value}

This callback is invoked when the value of the scroll bar is changed while the
indicator is being dragged.  This is implemented by calling the function stored
in \cl{scroll-bar-drag-callback} with two arguments, the scroll bar and the new
value.

The \cl{value-changed-callback} is invoked only after the indicator is released
after dragging it.

\callback {scroll-to-top-callback} {scroll-bar client gadget-id}
\callback {scroll-to-bottom-callback} {scroll-bar client gadget-id}
\callback {scroll-up-line-callback} {scroll-bar client gadget-id}
\callback {scroll-up-page-callback} {scroll-bar client gadget-id}
\callback {scroll-down-line-callback} {scroll-bar client gadget-id}
\Callback {scroll-down-page-callback} {scroll-bar client gadget-id}

All of the callbacks above are invoked when appropriate parts of the scroll bar
are clicked on.  Note that each implementation may not have ``hot spots''
corresponding to each of these callbacks.

\Defmethod {gadget-value} {(button \cl{scroll-bar})}

Returns a real number within the specified range.

\Defclass {scroll-bar-pane}

The instantiable class that implements a portable scroll bar; a subclass of
\cl{scroll-bar}.


\Gadget {slider}

The \cl{slider} gadget corresponds to a slider.

\Defclass {slider}

The instantiable class that implements an abstract slider.  This is a subclass
of \cl{value-gadget}, \cl{oriented-gadget-mixin}, \cl{range-gadget-mixin}, and
\cl{labelled-gadget-mixin}.

\definitarg {:drag-callback}
\definitarg {:show-value-p}
\Definitarg {:decimal-places}

Specifies the drag callback for the slider, whether the slider should show its
current value, and how many decimal places to the right of the decimal point
should be displayed when the slider is showing its current value.

\definitarg {:min-label}
\definitarg {:max-label}
\Definitarg {:range-label-text-style}

Specifies a label to be used at the low end and high end of the sldier, and what
the text style of those labels should be.

\definitarg {:number-of-tick-marks}
\Definitarg {:number-of-quanta}

Specifies the number of tick marks that should be drawn on the scroll bar, and
the number of quanta in the scroll bar.  If the scroll bar is quantized, the
scroll bar will consist of discrete values rather than continuous values.

\Defgeneric {gadget-show-value-p} {slider}

Returns \term{true} if the slider shows its value, otherwise returns \term{false}

\Defgeneric {slider-drag-callback} {slider}

Returns the function that will be called when the indicator of the slider is
dragged.  This function will be invoked with a two arguments, the slider and the
new value.

When this function returns \cl{nil}, that indicates that there is no drag
callback for the gadget.

\Callback {drag-callback} {slider client gadget-id value}

This callback is invoked when the value of the slider is changed while the
indicator is being dragged.  This is implemented by calling the function stored
in \cl{slider-drag-callback} with two arguments, the slider and the new value.

The \cl{value-changed-callback} is invoked only after the indicator is released
after dragging it.

\Defmethod {gadget-value} {(button \cl{slider})}

Returns a real number within the specified range.

\Defclass {slider-pane}

The instantiable class that implements a portable slider; a subclass of
\cl{slider}.


\subsection {The {\tt radio-box} and {\tt check-box} Gadgets}

Radio boxes and check boxes are special kinds of gadgets that constrain one or
more toggle buttons.  At any one time, only one of the buttons managed by the
radio box, or zero or more of the buttons managed by a check box, may be ``on''.
The contents of a radio box or a check box are its buttons, and as such a radio
box or check bnox is responsible for laying out the buttons that it contains.  A
radio box or check box is a client of each of its buttons so that the value of
the radio or check box can be properly computed.

As the current selection changes, the previously selected button and the newly
selected button both have their \cl{value-changed-callback} handlers invoked.

\Defclass {radio-box}

The instantiable class that implements an abstract radio box, that is, a gadget
that constrains a number of toggle buttons, only one of which may be selected at
any one time.  It is a subclass of \cl{value-gadget} and
\cl{oriented-gadget-mixin}.

\Definitarg {:current-selection}

This is used to specify which button, if any, should be initially selected.

\defgeneric {radio-box-current-selection} {radio-box}
\Defgeneric {(setf radio-box-current-selection)} {button radio-box}

Returns (or sets) the current selection for the radio box.  The current
selection will be one of the toggle buttons in the box.

\Defgeneric {radio-box-selections} {radio-box}

Returns a sequence of all of the selections in the radio box.  The elements of
the sequence will be toggle buttons.

\Defmethod {gadget-value} {(button \cl{radio-box})}

Returns the selected button.  This will return the same value as
\cl{radio-box-current-selection}

\Defclass {radio-box-pane}

The instantiable class that implements a portable radio box; a subclass of
\cl{radio-box}.


\Defclass {check-box}

The instantiable class that implements an abstract check box, that is, a gadget
that constrains a number of toggle buttons, zero or more of which may be
selected at any one time.  It is a subclass of \cl{value-gadget} and
\cl{oriented-gadget-mixin}.

\Definitarg {:current-selection}

This is used to specify which buttons, if any, should be initially selected.

\defgeneric {check-box-current-selection} {check-box}
\Defgeneric {(setf check-box-current-selection)} {button check-box}

Returns (or sets) the current selection for the check box.  The current
selection will be a list of zero or more of the toggle buttons in the box.

\Defgeneric {check-box-selections} {check-box}

Returns a sequence of all of the selections in the check box.  The elements of
the sequence will be toggle buttons.

\Defmethod {gadget-value} {(button \cl{check-box})}

Returns the selected buttons as a list.  This will return the same value as
\cl{check-box-current-selection}

\Defclass {check-box-pane}

The instantiable class that implements a portable check box; a subclass of
\cl{check-box}.


\Defmacro {with-radio-box} {(\rest options \key (type \cl{:one-of}) \allow) \body body} 

Creates a radio box whose buttons are created by the forms in \arg{body}.  The
macro \cl{radio-box-current-selection} can be wrapped around one of forms in
\arg{body} in order to indicate that that button is the current selection.

If \arg{type} is \cl{:one-of}, a \cl{radio-box} will be created.  If \arg{type}
is \cl{:some-of}, a \cl{check-box} will be created.

For example, the following creates a radio box with three buttons in it, the
second of which is initially selected.

\begin{verbatim}
(with-radio-box ()
  (make-pane 'toggle-button :label "Mono")
  (radio-box-current-selection
    (make-pane 'toggle-button :label "Stereo"))
  (make-pane 'toggle-button :label "Quad"))
\end{verbatim}

The following simpler form can also be used when the programmer does not need to
control the appearance of each button closely.

\begin{verbatim}
(with-radio-box ()
  "Mono" "Stereo" "Quad")
\end{verbatim}


\subsection {The {\tt list-pane} and {\tt option-pane} Gadgets}

\Defclass {list-pane}

The instantiable class that implements an abstract list pane, that is, a gadget
whose semantics are similar to a radio box or check box, but whose visual
appearance is a list of buttons.  It is a subclass of \cl{value-gadget}.

\Definitarg {:mode}

Either \cl{:nonexclusive} or \cl{:exclusive}.  When it is \cl{:exclusive}, the
list pane acts like a radio box, that is, only a single item can be selected.
Otherwise, the list pane acts like a check box, in that zero or more items can
be selected. The default is \cl{:exclusive}.

\definitarg {:items}
\definitarg {:name-key}
\definitarg {:value-key}
\Definitarg {:test}

The \cl{:items} initarg specifies a sequence of items to use as the items of the
list pane.  The name of the item is extracted by the function that is the value
of the \cl{:name-key} initarg, which defaults to \cl{princ-to-string}.  The
value of the item is extracted by the function that is the value of the
\cl{:value-key} initarg, which defaults to \cl{identity}.  The \cl{:test}
initarg specifies a function of two arguments that is used to compare items; it
defaults to \cl{eql}.

For example,

\begin{verbatim}
(make-pane 'list-pane
  :value '("Lisp" "C++")
  :mode :nonexclusive
  :items '("Lisp" "Fortran" "C" "C++" "Cobol" "Ada")
  :test 'string=)
\end{verbatim}

\Defmethod {gadget-value} {(button \cl{list-pane})}

Returns the single selected item when the mode is \cl{:exclusive}, or a sequence
of selected items when the mode is \cl{:nonexclusive}.

\Defclass {generic-list-pane}

The instantiable class that implements a portable list pane; a subclass of
\cl{list-pane}.

\Defclass {option-pane}

The instantiable class that implements an abstract option pane, that is, a
gadget whose semantics are identical to a list pane, but whose visual appearance
is a single push button which, when pressed, pops up a menu of selections..  It
is a subclass of \cl{value-gadget}.

\Definitarg {:mode}

Either \cl{:nonexclusive} or \cl{:exclusive}.  When it is \cl{:exclusive}, the
option pane acts like a radio box, that is, only a single item can be selected.
Otherwise, the option pane acts like a check box, in that zero or more items can
be selected. The default is \cl{:exclusive}.

\definitarg {:items}
\definitarg {:name-key}
\definitarg {:value-key}
\Definitarg {:test}

The \cl{:items} initarg specifies a sequence of items to use as the items of the
option pane.  The name of the item is extracted by the function that is the value
of the \cl{:name-key} initarg, which defaults to \cl{princ-to-string}.  The
value of the item is extracted by the function that is the value of the
\cl{:value-key} initarg, which defaults to \cl{identity}.  The \cl{:test}
initarg specifies a function of two arguments that is used to compare items; it
defaults to \cl{eql}.

For example,

\begin{verbatim}
(make-pane 'option-pane
  :value '("Lisp" "C++")
  :mode :nonexclusive
  :items '("Lisp" "Fortran" "C" "C++" "Cobol" "Ada")
  :test 'string=)
\end{verbatim}

\Defmethod {gadget-value} {(button \cl{option-pane})}

Returns the single selected item when the mode is \cl{:exclusive}, or a sequence
of selected items when the mode is \cl{:nonexclusive}.

\Defclass {generic-option-pane}

The instantiable class that implements a portable option pane; a subclass of
\cl{option-pane}.


\Gadget {text-field}

The \cl{text-field} gadget corresponds to a small field containing text.

\Defclass {text-field}

The instantiable class that implements an abstract text field.  This is a subclass of
\cl{value-gadget} and \cl{action-gadget}.

The value of a text field is the text string.  

\Definitarg {:editable-p}

This is used to specify whether or not the text field may be edited.

\Defmethod {gadget-value} {(button \cl{text-field})}

Returns the resulting string.

\Defclass {text-field-pane}

The instantiable class that implements a portable text field; a subclass of
\cl{text-field}.


\Gadget {text-editor}

The \cl{text-editor} gadget corresponds to a large field containing multiple
lines of text.

\Defclass {text-editor}

The instantiable class that implements an abstract large text field.  This is a
subclass of \cl{text-field}.

The value of a text editor is the text string.  

\definitarg {:ncolumns}
\Definitarg {:nlines}

Specifies the width and height of the text editor in columns and number of lines.

\Defmethod {gadget-value} {(button \cl{text-editor})}

Returns the resulting string.

\Defclass {text-editor-pane}

The instantiable class that implements a portable text editor; a subclass of
\cl{text-editor}.


\section {Integrating Gadgets and Output Records}

In addition to gadget panes, CLIM allows gadgets to be used inside of CLIM
stream panes.  For instance, an \cl{accepting-values} whose fields consist of
gadgets may appear in an ordinary CLIM stream pane.

Note that many of the functions in the output record protocol must correctly
manage the case where there are gadgets contained within output records.  For
example, \cl{(setf* output-record-position)} may need to notify the host window
system that the toolkit object representing the gadget has moved,
\cl{window-clear} needs to deactive any gadgets, and so forth.

\Defclass {gadget-output-record}

The instantiable class the represents an output record class that contains a
gadget.  This is a subclass of \cl{output-record}.

\Defmacro {with-output-as-gadget} {(stream \rest options) \body body} 

Invokes \arg{body} to create a gadget, and then creates a gadget output record
that contains the gadget and install's it into the output history of the output
recording stream \arg{stream}.  The returned value of \arg{body} must be the
gadget.

The options in \arg{options} are passed as initargs to the call to
\cl{invoke-with-new-output-record} that is used to create the gadget output
record.

The \arg{stream} argument is not evaluated, and must be a symbol that is bound to
an output recording stream.  If \arg{stream} is \cl{t}, \cl{*standard-output*} is
used.  \arg{body} may have zero or more declarations as its first forms.

For example, the following could be used to create an output record containing a
radio box that itself contains several toggle buttons:

\begin{verbatim}
(with-output-as-gadget (stream)
  (let* ((radio-box
           (make-pane 'radio-box 
             :client stream :id 'radio-box)))
    (dolist (item sequence)
      (make-pane 'toggle-button 
        :label (princ-to-string (item-name item))
        :value (item-value item)
        :id item :parent radio-box))
    radio-box))
\end{verbatim}

A more complex (and somewhat contrived) example of a push button that calls back
into the presentation type system to execute a command might be as follows:

\begin{verbatim}
(with-output-as-gadget (stream)
  (make-pane 'push-button
    :label "Click here to exit"
    :activate-callback
      #'(lambda (button)
          (declare (ignore button))
          (throw-highlighted-presentation
            (make-instance 'standard-presentation
              :object `(com-exit ,*application-frame*)
              :type 'command)
            *input-context*
            (make-instance 'pointer-button-press-event
              :sheet (sheet-parent button)
              :x 0 :y 0
              :modifiers 0
              :button +pointer-left-button+)))))
\end{verbatim}
