@node Part III Popups
@chapter Popups

Popup is not an object class. In contrast to normal objects popups are
only shown for a short time in their own window and, while they are
shown, no interaction with other objects is possible. So they don't
fit directly into the normal event loop where one waits for user
actions via @code{@ref{fl_do_forms()}}. Instead, when used stand-alone
(e.g.@: for a context menu) they are shown on a call of the function
@code{@ref{fl_popup_do()}}, which returns when the the user is done
with the popup and it has been removed from the screen. Only idle
callbacks and timers etc.@: are executed in the background while a
popup is being shown.

Popups are the building blocks for menu and selector objects, which
internally create and use popups. Thus it might be helpful to
understand how popups work to get the most out of these objects.

All functions dealing with popups have names starting with
@code{'fl_popup_'}, functions for individual entries start with
@code{'fl_popup_entry_'} and typedefs as well as macros with
@code{'FL_POPUP_'}. 

@ifnottex

@menu
* Adding Popups:          Adding Popups
* Popup Interaction:      Popup Interaction
* Other Popup Routines:   Other Popup Routines
* Popup Attributes:       Popup Attributes
@end menu

@end ifnottex

@node Adding Popups
@section Adding Popups

There are two ways to create and populate a popup with entries. The
first method, that allows more fine-grained control consists of first
generating a popup and then adding entries. Using this method all the
properties of entries can be set immediately. The second method, to be
discussed later, is simpler and may be sufficient for many
applications, and internally uses the first method.

To define a new popup using the more general interface call
@findex fl_popup_add()
@anchor{fl_popup_add()}
@example
FL_POPUP *fl_popup_add(Window win, const char *title);
@end example
@noindent
The function returns the address of the new popup on success and
@code{NULL} on failure. @code{win} is the window of a parent object
(use @code{@ref{FL_ObjWin()}} to find out about it). You can also use
@code{fl_root} for the root window, with @code{None} having the same
effect . @code{title} is an optional string that gets shown at the top
of the popup in a framed box. If not wanted pass an empty string or
@code{NULL}. The function returns a pointer to a new popup or
@code{NULL} on failure.

The title may contain embedded newline characters, this allows to
create titles that span more than one line.)

There is no built-in limit to the number of popups that can be
created.

Once you have popup you may add one or more entries by using
@findex fl_popup_add_entries()
@anchor{fl_popup_add_entries()}
@example
FL_POPUP_ENTRY *fl_popup_add_entries(FL_POPUP *popup,
                                     const char *entries, ...);
@end example
@noindent
On success the return value is the address of the first entry created
and @code{NULL} on failure. The first argument, @code{entries}, is a
pointer to the popup the new entry (or entries) is added to. The
second argument, @code{entries}, encodes information about the entries
to add. In the most simple case it consists just of the entries texts,
separated by @code{|} characters, e.g. @w{@code{"Item 1|Item 2|Item
3"}}. This would create three simple entries in the popup with labels
@code{"Item 1"}, @code{"Item 2"} and @code{"Item 3"}.

The @code{entries} string may contain newline characters which allows
to create entries that span more than a single line.

There's no built-in limit to the number of entries than be added to a
popup. @code{@ref{fl_popup_add_entries()}} can be called repeatedly to
append further entries to a popup.

It often is necessary to have more complex entries. E.g.@: one may
want to have keyboard shortcuts for entries, which are shown on the
right hand side of an entry, one may want to have sub-popups or set
callbacks etc. This can be achieved by embedding special character
sequences within the string describing the entries and passing further
arguments to the function, similar to the use of a format string in
e.g.@: @code{printf(3)}. All special sequences start with a @code{%}.

The following sequences are recognized:
@table @code
@item %x
Set a value of type @code{long int} that's passed to all callback
routines for the entry. The value must be given in the arguments
following the @code{entries} string.

@item %u
Set a @code{user_void} pointer that's passed to all callbacks of the
entry. The pointer must be specified in the arguments following the
@code{entries} string.

@item %f
Set a callback function that gets called when the entry is selected.
The function is of type
@example
int callback(FL_POPUP_RETURN *r);
@end example
Information about the entry etc.@: gets passed to the callback function
via the @code{FL_POPUP_RETURN} structure (see below) and the return
value of the function can be used to keep the selection being reported
back to the caller of @code{@ref{fl_popup_do()}} by returning a value
of @code{FL_IGNORE} (-1). The functions address must be given in the
arguments following the @code{entries} string.

@item %E
Set a callback routine that gets called each time the mouse enters the
entry (as long as the entry isn't disabled or hidden). The type of the
function is the same as that of the callback function for the
selection of the item but it's return value is never used. The
functions address must be given in the arguments following the
@code{entries} string.

@item %L
Set a callback routine that gets called each time the mouse leaves the
entry. The type of the function is the same as that of the callback
function for the selection of the entry but it's return value is never
used. The functions address must be given in the arguments following
the @code{entries} string.

@item %m
When this is specified a sub-popup gets opened when the mouse enters the
entry (the entry itself thus can't be selected). The sub-popup to be
opened must be an already existing popup and its address must be given
in the arguments following the @code{entries} string. A triangle will
be drawn on the right of the entry to indicate that it's an entry
for a sub-popup.

Mutually exclusive with @code{%t}, @code{%T}, @code{%r}, @code{%R}
and @code{%l}.

@item %t
@itemx %T
This makes the entry a "toggle" entry, an entry that represents binary
states and gets a check-mark drawn on its left if in "on" state. If
created with @code{%t} its in "off" state at the start, if created with
@code{"T"} its in "on" state. Switching states happens automatically
when the entry is selected.

Mutually exclusive with @code{%m}, @code{%r}, @code{%R} and @code{%l}.

@item %r
@itemx %R
This makes the entry a "radio" entry, i.e.@: it becomes part of a
group of entries of which only one can be "on" at a time. The group,
an integer value (don't use @code{INT_MIN} and @code{INT_MIN}), must
be given in the arguments following the @code{entries} string.

Radio entries are drawn with a small circle to the left, with the one
for the entry in "on" state filled with a color (blue per default).
When a radio entry is selected by the user that was in "off" state the
entry of the group that was is "on" state before is automatically
switched to "off" state.

If the entry gets created with @code{%r} the entry is in "off" state,
if created with @code{%R} it's in "on" state (in that case all entries
created before in "on" state are reset to "off" state, i.e.@: the
one created last "wins").

Mutually exclusive with @code{%m}, @code{%t}, @code{%T} and @code{%l}.

@item %l
This creates not a real entry but indicates that a line is to be drawn 
to visually group other entries. While other properties can be set for
such an "entry" only the "hidden" property (see below) is taken into
acount.

Mutually exclusive with @code{%m}, @code{%t}, @code{%T}, @code{%} and
@code{%R}.

@item %d
Marks the entry as disabled, i.e.@: it can't be selected and its text is
per default drawn in a different color
@item %h
Marks the entry as hidden, i.e.@: it is not shown while in this state.

@item %S
For entries with shortcut keys it's quite common to have them shown on
the right hand side. Using @code{%S} you can split the entrys text
into two parts, the first one (before @code{%S}) being drawn flushed
left and the second part flushed right. Note that using this special
sequence doesn't automatically sets a shortcut key, this still has to
be done using @code{%s}.

@item %s
Sets one or more shortcut keys for an entry. Requires a string with
the shortcuts in the arguments following the @code{entries} string.
@xref{Shortcuts}, for details on how to define shortcuts. Please note
that the character in the label identical to the shortcut character is
only shown as underlined if @code{%S} isn't used.

@item %%
Use this to put a @code{%} character within the text of an entry.
@end table

Please note that since @code{@ref{fl_popup_add_entries()}} is a
variadic function (i.e.@: it takes a variable number of arguments)
only very limited error checking is possible and thus it is of
importance that the arguments passed to the function have exactly the
required types!

The return value of @code{@ref{fl_popup_add_entries()}} is a pointer
to the first of the entries created. Since entries are stored as a
linked list this value can be used to iterate over the list (see below
for more information about the @code{@ref{FL_POPUP_ENTRY}} structure).
If the function returns @code{NULL} no entries were created.

A typical piece of code creating a popup may look like this:
@example
int save_cb(FL_POPUP_RETURN *result) @{
    ...
@}

int main(int argc, char *argv[]) @{
   FL_POPUP *popup;
   File *fp;

   ...

   popup = fl_popup_add(None, NULL);
   fl_popup_add_entries(popup,
                        "Save%SCtrl+S%s%f%u|"
                        "Quit%SEsc%s|"
                        "%l|"
                        "Work Offline%SCtrl+O%T%s",
                        "^S", save_cb, (void *) fp,
                        "^[",
                        "^O");
    ...
@}
@end example
@noindent
This creates a popup with three entries. The first one has the label
@code{"Save"} shown at the left and @code{"Ctrl+S"} at the right can
be selected by pressing @code{<Ctrl>S}, in which case the function
@code{save_cb()} will be invoked with a pointer to a structure that,
beside other informations, contains the file pointer @code{fp}. The
second entry has the labels @code{"Quit"} and @code{"Esc"} and it's
shortcut key is set to @code{<Esc>}. Below this entry a separator line
is drawn, followed by the third entry with labels @code{"Work
Offline"} and @code{"Ctrl+O"} and shortcut key @code{<Ctrl>O}. This
label is a "toggle" entry in "on" state, thus a check-marker is shown
beside it.

A few remarks about the callback routines. All have a type of
@code{FL_POPUP_CB} as given by this @code{typedef}:
@anchor{FL_POPUP_CB}
@tindex FL_POPUP_CB
@example
typedef int (*FL_POPUP_CB)(FL_POPUP_RETURN *);
@end example
@noindent
There are three kinds of callbacks, all with the same type. Whenever
an item is entered (by moving the mouse on top of it or with the
keyboard) its enter callback function is invoked (if one is set).
Exceptions are entries that are disabled or hidden or entries, that
just stand for separator lines. When an entry that can receive enter
callbacks is left, its leave callback is invoked.

Leave callbacks are not called when a selection has been made.
Instead, only the selection callback for the selected entry is
invoked.

A "sub-popup entry", i.e.@: an entry that when entered results in a
sub-popup to open, also can have an enter callback. Its leave
callback is not called when the user moves the mouse onto the
sub-popup but only once the sub-popup has been closed again and the
mouse has been moved off the sub-popup entry.

While enter and leave callback functions are defined to return an
integer value, it's never used. But for the third kind of callback,
invoked on selection of an entry, this isn't true. Instead, the
callbacks return value is important: if it is @code{FL_IGNORE} (-1),
the selection isn't reported back to the caller (and following
callbacks also aren't called). This can be useful when the callback
function already does everything required and nothing is left to be
done.

All callbacks receive a pointer to a structure of the type
@code{FL_POPUP_RETURN}:
@anchor{FL_POPUP_RETURN}
@tindex FL_POPUP_RETURN
@example
typedef struct @{
    long int              val;       /* value assigned to entry */
    void                 *user_data; /* pointer to user data */
    const char           *text;      /* text of selected popup entry */
    const char           *label;     /* text drawn on left */        
    const char           *accel;     /* text drawn on right */
    const FL_POPUP_ENTRY *entry;     /* selected popup entry */
    const FL_POPUP       *popup;     /* (sub-) popup it belongs to */
@} FL_POPUP_RETURN;
@end example

@code{val} is the value set by @code{"%x"}. If @code{"%x"} wasn't
given, it's an automatically generated value: when a popup is created
with @code{@ref{fl_popup_add_entries()}} a counter is initalized to 0.
Whenever an entry gets added the value of the counter is assigned to
the entry and then incremented. Unless a different value is set
explicitely via @code{"%x"} the first entry added to a popup thus gets
a value @code{val} of 0, the second one gets 1 etc. This even holds
for entries that just stand for separator lines. In simple situations
the value of @code{val} is probably sufficient to identify which entry
got selected.

Please note: it is possible that by setting the @code{val} members two
or more structures for items of the same popup get the same value. It
is the programmers responsibility to avoid that (unless, of course,
that's just what you intended).

The @code{user_data} member of the structure is the @code{user_void}
pointer set via @code{"%u"}. It allows to pass more complex data to
the callback function (or have returned on selection of an entry.

The @code{text} member is exactly the string used to create the entry,
including all the special sequences starting with @code{'%'}.
@code{label} is what's left after all those sequences as well as
backspace characters have been removed, tabs replaced by single spaces
and the string is split at @code{"%S"}. I.e.@: it's exactly what's
drawn left-flushed for the entry in the popup. @code{accel} is then
what's left after clean-up and came after @code{"%S"}, i.e.@: it's
what appears as the right-flushed text of the entry. Please note that
one or more of these pointers could under some circumstances be
@code{NULL}.

Finally, the two member @code{entry} and @code{popup} are pointers to
the entry itself and the popup the callback function is invoked for -
to find out the popup the selected entry itself belongs to use the
@code{popup} member of the entrys @code{@ref{FL_POPUP_ENTRY}}
structure.

Please note: while in a callback you are only allowed to change the
values of the @code{val} and @code{user_data} members. This can be
useful in the case of a cascade of selection callback calls since all
the selection callbacks receive the same structure (and this is also
the structure that finally gets passed back to the caller of
@code{@ref{fl_popup_do()}}) at the end in order to implement more
complex information interchange between the callbacks involved.

The elements of a @code{FL_POPUP_ENTRY} structure that might be of
interest) are
@anchor{FL_POPUP_ENTRY}
@tindex FL_POPUP_ENTRY
@example
typedef @{
    FL_POPUP_ENTRY *prev;    /* previous popup entry */
    FL_POPUP_ENTRY *next;    /* next popup entry */
    int             type;    /* normal, toggle, radio, sub-popup, line*/
    unsigned int    state;   /* disabled, hidden, checked */
    int             group;   /* group (for radio entries only) */
    FL_POPUP       *sub;     /* sub-popup bound to entry */
    ...
@} FL_POPUP_ENTRY;
@end example
@noindent
Note that you should not change the members of a
@code{@ref{FL_POPUP_ENTRY}} structure directly! Use the appropriate
functions documented below to modify them instead.

@code{prev} and @code{next} are pointers to the previous and the
following popup entry (or @code{NULL} if none exists).

@code{type} tells what kind of popup entry this is. There are five
different types:
@table @code
@anchor{FL_POPUP_NORMAL}
@tindex FL_POPUP_NORMAL
@item FL_POPUP_NORMAL
Normal popup entry with no special properties
@anchor{FL_POPUP_TOGGLE}
@tindex FL_POPUP_TOGGLE
@item FL_POPUP_TOGGLE
"Toggle" or "binary" entry, drawn with a check-mark to its left if in
"on" state
@anchor{FL_POPUP_RADIO}
@tindex FL_POPUP_RADIO
@item FL_POPUP_RADIO
Radio entry, drawn with a circle to its left (color-filled when "on".
The @code{group} member of the @code{@ref{FL_POPUP_ENTRY}} structure
determines to which group the entry belongs.
@anchor{FL_POPUP_SUB}
@tindex FL_POPUP_SUB
@item FL_POPUP_SUB
Entry for a sub-popup. The @code{sub} member of its
@ref{FL_POPUP_ENTRY} structure is a pointer to the sub-popup
that gets shown when the mouse enters the entry.
@anchor{FL_POPUP_LINE}
@tindex FL_POPUP_LINE
@item FL_POPUP_LINE
Not a "real" entry, just indicates that a separator line is to be
drawn between the previous and the next entry.
@end table

Finally, the @code{state} member can have the following values:
@table @code
@anchor{FL_POPUP_NONE}
@tindex FL_POPUP_NONE
@item FL_POPUP_NONE
No special state is set for the entry, the default.
@anchor{FL_POPUP_DISABLED}
@tindex FL_POPUP_DISABLED
@item FL_POPUP_DISABLED
The entry is disabled, i.e.@: isn't selectable (and normally is drawn in
a way to indicate this).
@anchor{FL_POPUP_HIDDEN}
@tindex FL_POPUP_HIDDEN
@item FL_POPUP_HIDDEN
The entry is not drawn at all (and thus can't be selected).
@anchor{FL_POPUP_CHECKED}
@tindex FL_POPUP_CHECKED
@item FL_POPUP_CHECKED
Only relevant for toggle and radio entries. Indicates that the state of
a toggle entry is "on" (drawn with a check-marker) and for a radio entry
that it is the one in "on" state of its group.
@end table
@noindent
The state can be a combination of the above constants by using a
bitwise OR.

The more interesting members of a @code{FL_POPUP} structure are
@tindex FL_POPUP
@example
typedef struct @{
    FL_POPUP       *next;        /* previously created popup */
    FL_POPUP       *prev;        /* later created popup */
    FL_POPUP       *parent;      /* for sub-popups: direct parent */
    FL_POPUP       *top_parent;  /* and top-most parent */
    Window          win;         /* window of the popup */
    FL_POPUP_ENTRY *entries;     /* pointer to list of entries */
    char           *title;       /* title string of the popup */
    ...
@} FL_POPUP;
@end example
@noindent
Note again that you are not supposed to change the members of the
structure.

Like popup entries also popups are stored in a (doubly) linked list.
Thus the @code{prev} and @code{next} members of the structure are
pointers to popups created earlier or later. If a popup is a sub-popup
of another popup then @code{parent} points to the next higher level
popup (otherwise it's @code{NULL}). In case there's a cascade of
popups the @code{top_parent} member points to the "root" popup (i.e.@:
the top-level popup), while for popups that aren't sub-popups it
always points back to the popup itself (in that case @code{parent} is
@code{NULL}).

@code{win} is the window created for the popup. It's @code{None} (0)
while the popup isn't shown, so it can be used to check if the popup
is currently visible.

The @code{entries} member points to the first element of the list of
entries of the popup. See the @code{@ref{FL_POPUP_ENTRY}} structure
documented above on how to iterate over all entries.

Finally, @code{title} is the title shown at the top of the popup (if
one is set). Never try to change it directly, there's the function
@code{@ref{fl_popup_set_title()}}, described below, for that.

To remove a popup entry use
@findex fl_popup_entry_delete()
@anchor{fl_popup_entry_delete()}
@example
int fl_popup_entry_delete(FL_POPUP_ENTRY *entry);
@end example
@noindent
The function return 0 on success and -1 if it failed for some reasons.
Note that the function for a sub-popup entry also deletes the popup
that was associated with the entry!

You may also insert one or more entries into a popup at
arbitrary places using
@tindex fl_popup_insert_entries()
@example
FL_POPUP_ENTRY *fl_popup_insert_entries(FL_POPUP *popup,
                                        FL_POPUP_ENTRY *after,
                                        const char *entries, ...);
@end example
@noindent
@code{popup} is the popup the entries are to be inserted in,
@code{after} is the entry after which the new entries are to be added
(use @code{NULL} if the new entries are to be inserted at the very
first position), and @code{entries} is the same kind if string as
already used in @code{@ref{fl_popup_add_entries()}}, including all the
available special sequences. The arguments indicated by @code{...}
have to be given according to the @code{entries} string.

Finally, when you don't need a popup anymore simply call
@tindex fl_popup_delete()
@example
int fl_popup_delete(FL_POPUP *popup);
@end example
@noindent
The function returns 0 on success and -1 on failure. It's not possible
to call the function while the popup is still visible on the screen.
Calling it from any callback function is problematic unless you know
for sure that the popup to be deleted (and sub-popups of it) won't be
used later and thus normally should be avoided.

Above was described how to first generate a popup and then populate
it. But there's also a (though less general) method to create and
populate a popup in a single function call. For this use
@findex fl_popup_create()
@anchor{fl_popup_create()}
@example
FL_POPUP *fl_popup_create(Window win, const char *title,
                          FL_POPUP_ITEM *items);
@end example
@noindent
The @code{win} and @code{title} arguments are the same as used in
@code{@ref{fl_popup_add()}}, i.e.@: they are parent window for the
popup (or @code{fl_root} or @code{None}) and the (optional, can be
@code{NULL}) title for the popup.

@code{items} is a pointer to an array of structures of the following
form:
@anchor{FL_POPUP_ITEM}
@tindex FL_POPUP_ITEM
@example
typedef struct @{
    const char  *text;        /* text of entry */
    FL_POPUP_CB  callback;    /* (selection) callback */
    const char  *shortcut;    /* keyboard shortcut description */
    int          type;        /* type of entry */
    int          state;       /* disabled, hidden, checked */
@} FL_POPUP_ITEM;
@end example
@noindent
The array must contain one structure for each entry of the popup and
must end in a structure where at least the @code{text} member is set
to @code{NULL}.

The @code{text} member describes the text of the entry. If it contains
the string @code{"%S"} the text is split up at this position and the
first part is used as the label drawn left-flushed for the entry and
the second part for the right-flushed part (for showing accelerator
keys etc.). Two more characters have a special meaning if they appear
at the very start of the string (and which then do not become part of
the label shown):
@table @code
@item '_'
Draw a separator line above this entry.
@item '/'
This entry is a sub-popup entry and the following elements of the
@code{items} array (until the first element with @code{text} set to
@code{NULL} define the entries of the sub-popup.
@end table
@noindent
Both @code{'_'} and @code{'/'} can appear at the start of the string,
it doesn't matter which one comes first.

The @code{callback} member is a function to be invoked when the entry
is selected (irrelevant for sub-popup entries). @code{shortcut} is a
string, encoding which keyboard shortcut keys can be used to select
the item (@pxref{Shortcuts}, for details on how such a string has to
be assembled).

@code{type} describes the type of the entry and must be one of
@code{@ref{FL_POPUP_NORMAL}}, @code{@ref{FL_POPUP_RADIO}} (all radio
entries automatically belong to the same group (numbered
@code{INT_MIN}). You can't use @code{@ref{FL_POPUP_LINE}} or
@code{@ref{FL_POPUP_SUB}}. If you want a sub-popup entry use
@code{@ref{FL_POPUP_NORMAL}} and set @code{'/'} as the first character
of the @code{text} member of the structure. If you need a separator
line put a @code{'_'} at the start of the @code{text} member string of
the entry which comes after the separator line.

Finally, the @code{state} member can be 0 or the bitwise or of
@code{@ref{FL_POPUP_DISABLED}}, @code{@ref{FL_POPUP_HIDDEN}} and
@code{@ref{FL_POPUP_CHECKED}}. The first one makes the entry appear
disabled and non-selectable, the second will keep the entry from being
drawn at all, and the third one puts the entry into "on" state
(relevant for toggle and radio entries only). If you try to set
@code{@ref{FL_POPUP_CHECKED}} for more than a single radio entry the
last one you set if for "wins", i.e.@: only this one will be in "on"
state. See below for a more detailed discussion of these entry
properties.

@code{@ref{fl_popup_create()}} does not allow to associate values or
pointers to user data to individual entries, set titles for
sub-popups, have radio entries belong to different groups or set enter
or leave callback functions (though there exist a number of functions
to remedy the situation in case such things are needed).

The function returns a pointer to the newly created popup (or
@code{NULL} on failure). You are guaranteed that each entry has been
assigned a unique value, starting at 0 and which is identical to the
index of corresponding element in the @code{items} array, i.e.@: the
first element results in an entry assigned 0, the second entry gets
1 etc.

All functions working on popups or entries can, of course, be used on
popups and their entries generated via @code{@ref{fl_popup_create()}}.
They can be employed to remedy some of the limitations imposed by the
simpler popup creation API.

Here's an example of how to create a popup using
@code{fl_popup_create()}:
@example
FL_POPUP *popup;

FL_POPUP_ITEMS items[] = @{
  @{"Item 1%S^1", NULL, "^1", FL_POPUP_NORMAL, FL_POPUP_NONE    @},
  @{"Item 2%S^2", NULL, "^2", FL_POPUP_RADIO,  FL_POPUP_CHECKED @},
  @{"Item 3%S^3", NULL, "^3", FL_POPUP_RADIO,  FL_POPUP_NONE    @},
  @{"_/Item 4",   NULL, NULL, FL_POPUP_NORMAL, FL_POPUP_NONE    @},
    @{"Sub-item A",  cbA, "^A", FL_POPUP_NORMAL, FL_POPUP_DISABLED@},
    @{"Sub-item B",  cbB, "^B", FL_POPUP_TOGGLE, FL_POPUP_NONE    @},
    @{NULL,         NULL, NULL, 0,               0                @},
  @{"Item 5",     NULL, NULL, FL_POPUP_NORMAL, FL_POPUP_NONE    @},
  @{NULL,         NULL, NULL, 0,               FL_POPUP_NONE    @}
@};

popup = fl_popup_create(None, "Test", items);
@end example
@noindent
This creates a new popup with the title @code{"Test"} and 5 entries as
well as a a sub-popup with two entries, that gets opened when the
mouse is over the entry labeled @code{"Item 4"}.

The first entry in the main popup has the label @code{"Item 1"} on the
left and @code{"^1"} of the right side. It has no callback routine and
can be selected via the @code{<Crtl>1} shortcut. It's just a normal
menu entry.

The second entry has the label @code{"Item 2"} on the left and
@code{"^2"} of the right side, also no callack and @code{<Crtl>2} as
its keyboard shortcut. It's a radio entry that is in "on" state. The
third entry is like the second, labels are @code{"Item 3"} and
@code{"^3"} and it reacts to @code{<Crtl>3}, except that it's in "off"
state. The second and third label belong to the same group (with the
group number set to @code{INT_MIN}), i.e.@: when the third entry gets
selected the second one gets switched to "off" state (and vice versa).

Before the fourth entry a separator line will be drawn (that's the
effect of its text starting with @code{'_'}. It's a sub-popup entry
(due to the @code{'/'} at the start of its text). It's label is simply
@code{"Item 4"} and no right hand label (but that isn't supposed to
indicate that sub-entries couldn't have shortcuts!). It has no
selection callback (which wouldn't sense make sense for a sub-popup
entry anyway).

The following three elements of the @code{items} array are for the
sub-popup that gets opened when the mouse is over the fourth item of
the main popup. In the sub-popup we first have an normal entry with
label @code{"Sub-item A"}. The function @code{cbA()} will be called
when this entry of the sub-popup is selected. Then we have a second
entry, labled @code{"Sub-item B"}, which is a currently disabled
toggle entry in "off" state. If it weren't disabled its selection
would result in the callback function @code{cbB()} getting called. The
next element of the @code{items} array, having @code{NULL} as its
@code{text} member, signifies the end of the sub-popup.

Now that we're done with the sub-popup another entry in the main popup
follows, a normal entry with just a left-label of @code{Item 5}. The
final element of @code{items}, where @code{text} is set to @code{NULL}
then signifies that this is the end of the popup.

As there are functions to append to and insert entries into a popup with
a kind of format string, followed by a variable list of arguments,
there are also functions for adding and inserting entries using an
array of @code{@ref{FL_POPUP_ITEM}}. These are
@anchor{fl_popup_add_items()}
@findex fl_popup_add_items()
@anchor{fl_popup_insert_items()}
@findex fl_popup_insert_items()
@example
FL_POPUP_ENTRY *fl_popup_add_items(FL_POPUP *popup,
                                   FL_POPUP_ITEM *items);
FL_POPUP_ENTRY *fl_popup_insert_items(FL_POPUP *popup,
                                      FL_POPUP_ENTRY *after,
                                      FL_POPUP_ITEM  *items);
@end example
@noindent
Both functions return the address of the first entry created on
success and @code{NULL} on error. The first argument is the popup the
entries are to be appended to or inserted into, the last argument the
array of items (as in the case of @code{@ref{fl_popup_create()}} at
least the @code{text} member of the last element must be a @code{NULL}
pointer to indicate the end). @code{fl_popup_insert_items()} takes
another argument, @code{after}, the entry after which the new entries
are to be inserted (if called with @code{after} set to @code{NULL} the
new entries are inserted at the very start of the popup).


@node Popup Interaction
@section Popup Interaction

A popup will be drawn on the screen when the function
@tindex fl_popup_do()
@anchor{fl_popup_do()}
@example
FL_POPUP_RETURN *fl_popup_do(FL_POPUP *popup);
@end example
@noindent
is called. It only returns when the user either selects an entry or
closes it in some other way (e.g.@: by clicking outside the popup's
area). When a selection was made the function returns a pointer to a
@code{@ref{FL_POPUP_RETURN}} structure with information about the
entry that was selected (please note that the structure is internal
storage belonging to the Forms Library and is re-used when the popup
is shown again, so copy out all data you may need to keep). If no
selection was made (or one of the invoked callback routines returned a
value of @code{FL_IGNORE} (-1) @code{NULL} is returned.

While the popup is shown the user can interact with the popup using
the mouse or the keyboard. When the mouse is hovering over a
selectable entry of the popup the entry is highlighted, when the mouse
reaches an entry for a sub-popup, the associated sub-popup
automatically gets opened. A selection is made by clicking on an entry
(or, in case that the popup was opened while a mouse button was
pressed down, when the mouse button is released). Clicking outside the
popups window (or, depending on the "policy", see below, releasing the
mouse button somewhere else than over a selectable item) closes the
popup without a selection being made.

Popups also can be controlled via the keyboard. First of all, on
pressing a key, the shortcuts set for items are evaluated and, if a
match is found, the corresponding entry is returned as selected (if
the popup currently shown is a sub-popup, first the shortcuts for this
sub-popup are checked, then those of its parent etc.@: until the
top-most popup has been reached and checked for). The user can also
navigate through the selectable entires using the @code{<Up>} and
@code{<Down>} arrow keys and open and close sub-popups with the
@code{<Right>} and @code{<Left>} cursor keys. Pressing the
@code{<Home>} key highlights the first (selectable) entry in the
popup, @code{<End>} the last one. By using the @code{<Esc>} key (or
@code{<Cancel>} if available) the currently shown popup is closed (if
an entry in a sub-popup was highlighted just this sub-popup is
closed). Finally, pressing @code{<Return>} while on a selectable entry
results in this entry being reported as selected.

Once the user has selected an entry its callback function is invoked
with a @code{@ref{FL_POPUP_RETURN}} structure as the argument. When
this function returns, the callback for the popup the entry belongs to
is called with exactly the same structure. If the popup is a
sub-popup, next the callback for its "parent" popup is invoked, again
with the same structure (except that the @code{popup} member is
changed each time to indicate which popup the call is made for).
Repeat until the callback for the top-most popup has been called.
Finally the structure used in all those callback invocations is
returned from @code{@ref{fl_popup_do()}}. This chain of callback calls
is interrupted when one of the callbacks returns a value of
@code{FL_IGNORE} (-1). In that case no further callbacks are invoked
and @code{@ref{fl_popup_do()}} returns @code{NULL}, i.e.@: from the
callers perspective it looks as if no selection has been made. This
can be useful when one of the callbacks was already was able to do all
the work required on a selection.

Per default a popup stays open when the user releases the mouse button
anywhere else than on a selectable entry. It only gets closed when the
user either selects an entry or clicks somewhere outside of the popup
area. An alternative is a "drag-down" popup that gets closed whenever
the mouse button is released, even if the mouse isn't on the area of
the popup or a selectable entry. To achieve this effect you can change
the "policy" using the function
@findex fl_popup_set_policy()
@anchor{fl_popup_set_policy()}
@example
int fl_popup_set_policy(FL_POPUP *popup, int policy);
@end example
@noindent
There are two values @code{policy} can have:
@table @code
@anchor{FL_POPUP_NORMAL_SELECT}
@tindex FL_POPUP_NORMAL_SELECT
@item FL_POPUP_NORMAL_SELECT
Default, popup stays open until mouse button is released on a
selectable entry or button is clicked outside the popups area.
@anchor{FL_POPUP_DRAG_SELECT}
@tindex FL_POPUP_DRAG_SELECT
@item FL_POPUP_DRAG_SELECT
Popup is closed when the mouse button is released anywhere.
@end table
@noindent
The function can be called with either a (valid) popup address, in
which case the policy for that popup is changed, or with a @code{NULL}
pointer to change the default setting of the policy, used in the
creation of new popups. The function returns the previous policy value
or -1 on errors.

It's also possible to determine the policy setting by using
@findex fl_popup_get_policy()
@anchor{fl_popup_get_policy()}
@example
int fl_popup_get_policy(Fl_POPUP *popup);
@end example
If called with the address of a (valid) popup the policy for this
popup (or its parent if one exists) gets returned. If called with a
@code{NULL} pointer the default policy used in creating new popups is
returned. On error -1gets returned.

Calling the function with @code{NULL} as the @code{popup} argument
changes the default setting for the popups created afterwards.

If the popup is partially off-screen the user can push the mouse at
the screen borders in the direction of the currently invisible popup
entries. This results in the popups window getting moved so that
previosuly invisible entries become accessible. The popup window gets
shifted vertically in single entry steps, in horizontal direction by a
tenth of the screen width. The delay between shifts is about @w{100
ms}.


@node Other Popup Routines
@section Other Popup Routines

When @code{@ref{fl_popup_do()}} is called the popup per default is
shown with its left upper corner at the mouse position (unless the
popup wouldn't fit onto the screen). Using
@findex fl_popup_set_position()
@anchor{fl_popup_set_position()}
@example
void fl_popup_set_position(FL_POPUP *popup, int x, int y);
@end example
@noindent
the position where the popup is drawn can be changed (but if it
wouldn't fit onto the screen at that position it will also changed
automatically). @code{x} and @code{y}. to be given relative to the
root window, define the position of the upper left hand corner. Using
this function for sub-popups is useless, they always get opened as
near as possible to the corresponding sub-popup entry.

When setting the position of a popup it can be useful to know the
exact sizes of its window in advance. These can be obtained by calling
@findex fl_popup_get_size()
@anchor{fl_popup_get_size()}
@example 
int fl_popup_get_size(FL_POPUP *popup, unsigned int *w, unsigned int
*h);
@end example
@noindent
The function returns 0 on success and -1 on error (in case the
supplied @code{popup} argument isn't valid). Please note that the
reported values are only valid until the popup is changed, e.g.@: by
adding, deleting or changing entries or changing the appearance of the
popup. 

A callback function @code{cb()} of type @code{@ref{FL_POPUP_CB}}, to
be called when a entry (or an entry of a sub-popup) is selected, can
be associated with a popup (or changed) using
@findex fl_popup_set_callback()
@anchor{fl_popup_set_callback()}
@example
typedef int (*FL_POPUP_CB)(FL_POPUP_RETURN *);
FL_POPUP_CB fl_popup_set_callback(FL_POPUP *popup, FL_POPUP_CB cb);
@end example
@noindent
The function returns the old setting of the callback routine (on error
@code{NULL} is returned, which may indistinguishable from the case
that no callback was set before).

For an entry all three associated callback functions can be set via
@findex fl_popup_entry_set_callback()
@anchor{fl_popup_entry_set_callback()}
@findex fl_popup_entry_set_enter_callback()
@anchor{fl_popup_entry_set_enter_callback()}
@findex fl_popup_entry_set_leave_callback()
@anchor{fl_popup_entry_set_leave_callback()}
@example
FL_POPUP_CB fl_popup_entry_set_callback(FL_POPUP_ENTRY *entry,
                                        FL_POPUP_CB cb);
FL_POPUP_CB fl_popup_entry_set_enter_callback(FL_POPUP_ENTRY *entry,
                                              FL_POPUP_CB enter_cb)
FL_POPUP_CB fl_popup_entry_set_leave_callback(FL_POPUP_ENTRY *entry,
                                              FL_POPUP_CB leave_cb);
@end example
@noindent
The first function sets the callback invoked when the entry is
selected, the second when the mouse enters the area of the entry and
the third, when the mouse leaves that area. All function return the
previously set callback or @code{NULL} when none was set or an error
occured. @code{NULL} also gets returned on errors.

There are three properties that can be set for a popup entry
@table @code
@tindex FL_POPUP_DISABLED
@item FL_POPUP_DISABLED
The entry is is shown as disabled and can't be selected.
@tindex FL_POPUP_HIDDEN
@item FL_POPUP_HIDDEN
The entry is not shown when the popup is opened.
@tindex FL_POPUP_CHECKED
@item FL_POPUP_CHECKED
Relevant only for toggle and redio entries. When set beside the label
of a toggle entry a check-marker is drawn while the circle beside a
radio button is drawn colored.
@end table
@noindent
The "state" of an entry is the binary OR of these values which can be
set and queried using the functions
@findex fl_popup_entry_set_state()
@anchor{fl_popup_entry_set_state()}
@findex fl_popup_entry_get_state()
@anchor{fl_popup_entry_get_state()}
@example
unsigned int fl_popup_entry_set_state(FL_POPUP_ENTRY *entry,
                                      unsigned int state);
unsigned int fl_popup_entry_get_state(FL_POPUP_ENTRY *entry);
@end example
@noindent
@code{@ref{fl_popup_entry_set_state()}} returns the previous state on
success and @code{UINT_MAX} (a value with all bits set) on failure.

Note that when setting @code{@ref{FL_POPUP_CHECKED}} for a radio entry
all other radio entries belonging to the same group automatically lose
their "on" (checked) property.

There are also three convenience function for clearing, raising and
toggling bits in the state of an entry. Normally to clear a certain
bit of the state you have to first call
@code{@ref{fl_popup_entry_get_state()}}, then clear the bit in the
return value and finally call @code{@ref{fl_popup_entry_set_state()}}
with the result to set the new state. Use of these convenience
functions allows to change state bits in a single call.
@findex fl_popup_entry_clear_state()
@anchor{fl_popup_entry_clear_state()}
@findex fl_popup_raise_clear_state()
@anchor{fl_popup_raise_clear_state()}
@findex fl_popup_toggle_clear_state()
@anchor{fl_popup_toggle_clear_state()}
@example
unsigned int fl_popup_entry_clear_state(FL_POPUP_ENTRY *entry,
                                        unsigned int what);
unsigned int fl_popup_entry_raise_state(FL_POPUP_ENTRY *entry,
                                        unsigned int what);
unsigned int fl_popup_entry_toggle_state(FL_POPUP_ENTRY *entry,
                                         unsigned int what);
@end example
The @code{what} argument can be any value resulting from a bitwise OR
of @code{@ref{FL_POPUP_DISABLED}}, @code{@ref{FL_POPUP_HIDDEN}} and
@code{@ref{FL_POPUP_CHECKED}} (thus you can clear, set or toggle one
or more bits of the state in a single call). The functions all return
the original value of the state.

You may search for an entry in a popup by different criteria (please
note that the search also includes sub-popups of the popup, you can
identify them by checking the @code{popup} member of the
@ref{FL_POPUP_ENTRY} structure). The search obviously will only
deliver reasonable results if what you're searching for is unique
between all the entries.

First, you can ask for the entry that had been created with a certain
text, including all the special sequences, by calling
@findex fl_popup_entry_get_by_text()
@anchor{fl_popup_entry_get_by_text()}
@example
FL_POPUP_ENTRY *fl_popup_entry_get_by_text(FL_POPUP *popup,
                                           const char *text);
@end example
@noindent
The function returns either a pointer to the entry found or
@code{NULL} on failure (because either no entry with this text was
found or the popup doesn't exist).

You may as well search by the left-flushed label parts of the entries
as shown on the screen (note that tab characters @code{'\t'}
originally embedded in the text used when creating the label have been
replaced by single spaces and backspace characters @code{'\b'} were
removed as well as all special sequences)
@findex fl_popup_entry_get_by_label()
@anchor{fl_popup_entry_get_by_label()}
@example
FL_POPUP_ENTRY *fl_popup_entry_get_by_label(FL_POPUP *popup,
                                            const char *label);
@end example
@noindent
Thus, since an entry created via a string like
@code{"I\bt%Tem\t1%SCtrl+X"} will shown with a left-flushed label part
of @code{"Item 1"}, this will found when searching with this string.

Another way to search for an entry is by its value as either specified
via the @code{"%x"} special sequence or assigned automatically by
@findex fl_popup_entry_get_by_value()
@anchor{fl_popup_entry_get_by_value()}
@example
FL_POPUP_ENTRY *fl_popup_entry_get_by_value(FL_POPUP *popup,
                                            long value);
@end example

Also the @code{user_data} pointer associated with the entry can be
used as the search criterion:
@findex fl_popup_entry_get_by_user_data()
@anchor{fl_popup_entry_get_by_user_data()}
@example
FL_POPUP_ENTRY *fl_popup_entry_get_by_user_data(FL_POPUP *popup,
                                                void *user_data);
@end example

Finally one can try to find an entry by its current position in the
popup (note that here sub-popups aren't taken into consideration since
that would make the meaning of "position" rather hard to define) by
@findex fl_popup_entry_get_by_position()
@anchor{fl_popup_entry_get_by_position()}
@example
FL_POPUP_ENTRY *fl_popup_entry_get_by_position(FL_POPUP *popup,
                                               long position);
@end example
@noindent
where @code{posistion} is starting with 0, so when called with 0 the
first entry will be returned, when called with 1 you get the second
entry etc. Note that separator lines aren't counted but entries
currently being hidden are.


@node Popup Attributes
@section Popup Attributes

Using
@findex fl_popup_set_title()
@anchor{fl_popup_set_title()}
@findex fl_popup_get_title()
@anchor{fl_popup_get_title()}
@example
void fl_popup_set_title(FL_POPUP *popup, const char *title);
const char *fl_popup_set_title(FL_POPUP *popup);
@end example
@noindent
the title of a popup can be changed or the currently set title
determined.

To query or set the font the popups title is drawn in use
@findex fl_popup_get_title_font()
@anchor{fl_popup_get_title_font()}
@findex fl_popup_set_title_font()
@anchor{fl_popup_set_title_font()}
@example
void fl_popup_get_title_font(FL_POPUP *popup, int *size, int *style);
void fl_popup_set_title_font(FL_POPUP *popup, int size, int style);
@end example
@noindent
@xref{Label Attributes and Fonts}, for details about the sizes and
styles that should be used. The default size and style are
@code{@ref{FL_NORMAL_SIZE}} and @code{@ref{FL_EMBOSSED_STYLE}}. This
setting also applies to sub-popups of the popup, thus setting a title
font for sub-popups is useless.

When called with the @code{popup} argument set to @code{NULL} the
default settings for popups generated later are returned or set.

Also the font for the entries of a popup can be queried or and set via
@findex fl_popup_entry_set_font()
@anchor{fl_popup_entry_set_font()}
@example
void fl_popup_entry_get_font(FL_POPUP *popup, int *style, int *size);
void fl_popup_entry_set_font(FL_POPUP *popup, int style, int size);
@end example
@noindent
The defalt size is @code{@ref{FL_NORMAL_SIZE}} and the default style
is @code{@ref{FL_NORMAL_STYLE}}. Again, the returned or set values
also apply to all sub-popups, so calling the function for sub-popups
doesn't make sense.

When called with @code{popup} set to @code{NULL} the default settings
for popups are returned or changed.

The width of a popup is calculated using the widths of the title
and the entries. You can influence this width by setting a minimum
width a popup should have. There are two functions for the minimum
width:
@findex fl_popup_get_min_width()
@anchor{fl_popup_get_min_width()}
@findex fl_popup_set_min_width()
@anchor{fl_popup_set_min_width()}
@example
int fl_popup_get_min_width(FL_POPUP *popup);
int fl_popup_set_min_width(FL_POPUP *popup, int min_width);
@end example
@noindent
The first one returns the currently set minimum width (a negative
return value indicates an error). The second allows sets a new minimum
width. Setting the minimum width to 0 or a negative value switches the
use of the minimum width off. It returns the previous value (or a
negative value on error).

You can query or set the border width popups are drawn width (per
default it's set to @code{1}). To this purpose call
@findex fl_popup_get_bw()
@anchor{fl_popup_get_bw()}
@findex fl_popup_set_bw()
@anchor{fl_popup_set_bw()}
@example
int fl_popup_get_bw(FL_POPUP *popup);
int fl_popup_set_bw(FL_POPUP *popup, int bw);
@end example
@noindent
Please note that the border width setting is automatically applied
also to sub-popups, so there's no good reason to call these functions
for sub-popups. The default border width is the same as that for
objects.

The functions can also be called with @code{popup} set to @code{NULL}
in which case the default setting for the border width is returned or
set, respectively.

To change the cursor that is displayed when a popup is shown use
@findex fl_popup_set_cursor()
@anchor{fl_popup_set_cursor()}
@example
void fl_popup_set_cursor(FL_POPUP *popup, int cursor_name);
@end example
@noindent
Use one of the symbolic cursor names (shapes) defined by standard X or
the integer value returned by @code{@ref{fl_create_bitmap_cursor()}}
or one of the Forms Library's pre-defined symbolic names for the
@code{cursor_name} argument.

Per default the cursor named @code{"XC_sb_right_arrow"} is used. If
the function is called with @code{popup} set to @code{NULL} the
default cursor for popups generated afterwards is changed.

There are several colors used in drawing a popup. These can be set
or queried with the functions
@findex fl_popup_set_color()
@anchor{fl_popup_set_color()}
@findex fl_popup_get_color()
@anchor{fl_popup_get_color()}
@example
FL_COLOR fl_popup_set_color(FL_POPUP *popup, int type,
                            FL_COLOR color);
FL_COLOR fl_popup_get_color(FL_POPUP *popup, int type);
@end example
@noindent
where @code{type} can be one of the following values:
@table @code
@anchor{FL_POPUP_BACKGROUND_COLOR}
@tindex FL_POPUP_BACKGROUND_COLOR
@item FL_POPUP_BACKGROUND_COLOR
Background color of the popup, default is @code{FL_MCOL}.
@anchor{FL_POPUP_HIGHLIGHT_COLOR}
@tindex FL_POPUP_HIGHLIGHT_COLOR
@item FL_POPUP_HIGHLIGHT_COLOR
Backgroud color an entry is drawn with when it's selectable and the
mouse is on top of it, default is @code{FL_BOTTOM_BCOL}.
@anchor{FL_POPUP_TITLE_COLOR}
@tindex FL_POPUP_TITLE_COLOR
@item FL_POPUP_TITLE_COLOR
Color used for the title text of a popup, default is @code{FL_BLACK}.
@anchor{FL_POPUP_TEXT_COLOR}
@tindex FL_POPUP_TEXT_COLOR
@item FL_POPUP_TEXT_COLOR
Color normal used for entry texts, default is @code{FL_BLACK}.
@anchor{FL_POPUP_HIGHLIGHT_TEXT_COLOR}
@tindex FL_POPUP_HIGHLIGHT_TEXT_COLOR
@item FL_POPUP_HIGHLIGHT_TEXT_COLOR
Color of the entry text when it's selectable and the mouse is on top
of it, default is @code{FL_WHITE}.
@anchor{FL_POPUP_DISABLED_TEXT_COLOR}
@tindex FL_POPUP_DISABLED_TEXT_COLOR
@item FL_POPUP_DISABLED_TEXT_COLOR
Color for drawing the text of disabled entries, default is
@code{FL_INACTIVE_COL}.
@anchor{FL_POPUP_RADIO_COLOR}
@tindex FL_POPUP_RADIO_COLOR
@item FL_POPUP_RADIO_COLOR
Color the circle drawn for radio entris in "on" state is drawn in.
@end table

When setting a new color the color previously used is returned by
@code{@ref{fl_popup_set_color()}}. Calling these functions for
sub-popups doesn't make sense since sub-popups are always drawn in the
colors set for the parent popup.

When called with @code{popup} set to @code{NULL} the functions return
or set the default colors of popups created afterwards.

To change the text of a popup entry call
@findex fl_popup_entry_set_text()
@anchor{fl_popup_entry_set_text()}
@example
int fl_popup_entry_set_text(FL_POPUP_ENTRY *entry, const char *text);
@end example
@noindent
Please note that in the text no special sequences except @code{"%S"}
(at which place the text is split to make up the left- and
right-flushed part of the label drawn) are recognized.

The shortcut keys for a popup label can be changed using
@findex fl_popup_entry_set_shortcut()
@anchor{fl_popup_entry_set_shortcut()}
@example
void fl_popup_entry_set_shortcut(FL_POPUP_ENTRY *entry,
                                 const char *shortcuts);
@end example
@noindent
@xref{Shortcuts}, for details on how such a string has to look like.

The value assigned to a popup entry can be changed via
@findex fl_popup_entry_set_value()
@anchor{fl_popup_entry_set_value()}
@example
long fl_popup_entry_set_value(FL_POPUP_ENTRY *entry, long value);
@end example
@noindent
The function returns the previous value.

Also the user data pointer associated with a popup entry can
be modified by calling
@findex fl_popup_entry_set_user_data()
@anchor{fl_popup_entry_set_user_data()}
@example
void *fl_popup_entry_set_user_data(FL_POPUP_ENTRY *entry,
                                   void *user_data);
@end example
@noindent
The function returns the previous setting of @code{user_data}.

To determine to which group a radio entry belongs call
@findex fl_popup_entry_get_group()
@anchor{fl_popup_entry_get_group()}
@example
int fl_popup_entry_get_group(FL_POPUP_ENTRY *entry);
@end example
@noindent
Obviously, this function only makes much sense when applied to radio
entries. It returns the group number on success and @code{INT_MAX} on
failure (that's why @code{INT_MAX} shouldn't be used for group
numbers).

To assign a radio entry to a different group call
@findex fl_popup_entry_set_group()
@anchor{fl_popup_entry_set_group()}
@example
int fl_popup_entry_set_group(FL_POPUP_ENTRY *entry, int group);
@end example
@noindent
Again, for obvious reasons, the function should normally only be
called for radio entries. It returns the previous group number on
success and @code{INT_MAX} on failure. If one of the entries of the new
group was in "on" state the entries state will be reset to "off" if
necessary.

For entries other than radio entries the group isn't used at all. So,
theoretically, it could be used to store a bit of additional
information. If that would be good programming practice is another
question...

Finally, the sub-popup associated with a sub-popup-entry can be
queried or changed using the functions
@findex fl_popup_entry_get_subpopup()
@anchor{fl_popup_entry_get_subpopup()}
@findex fl_popup_entry_set_subpopup()
@anchor{fl_popup_entry_set_subpopup()}
@example
FL_POPUP *fl_popup_entry_get_subpopup(FL_POPUP_ENTRY *entry);
FL_POPUP *fl_popup_entry_get_subpopup(FL_POPUP_ENTRY *entry,
                                      FL_POPUP *subpopup);
@end example
@noindent
Obviously, calling these functions only makes sense for sub-popup
entries.

@code{@ref{fl_popup_entry_get_subpopup()}} returns the address of the
sub-popup associated with the entry or @code{NULL} on failure.

To change the sub-popup of an entry a valid sub-popup must be passed
to @code{@ref{fl_popup_entry_set_subpopup()}}, i.e.@: the sub-popup
must not already be a sub-popup of another entry or the popup the
entry belongs to itself. You also can't set a new sub-popup while the
old sub-popup associated with the entry or the popup to become the new
sub-popup is shown. On success the address of the new sub-popup is
returned, on failure @code{NULL}.

Note that this function deletes the old sub-popup that was associated
with the popup.
