Amiga® RKM Libraries: 15 GadTools Library

GadTools is a new library in Release 2 that is designed to simplify the
task of creating user interfaces with Intuition.  GadTools offers a
flexible and varied selection of gadgets and menus to help programmers
through what used to be a difficult chore.

Intuition, the Amiga's graphical user interface, is a powerful and
flexible environment.  It allows a software designer a great degree of
flexibility in creating dynamic and powerful user interfaces.  However,
the drawback of this flexibility is that programming even straightforward
user interfaces can be complicated, and certainly difficult for first-time
Intuition programmers.

What the Gadget Toolkit (GadTools) attempts to do is harness the power of
Intuition by providing easy-to-use, high-level chunks of user interface.
GadTools doesn't pretend to answer all possible user interface needs of
every application but by meeting the user interface needs of most
applications, GadTools greatly simplifies the problem of designing
user-friendly software on the Amiga.  (For applications with special
needs, custom solutions can be created with Intuition's already-familiar
gadgets or its new Boopsi object-oriented custom gadget system; GadTools
is compatible with these.)

 Elements of GadTools    GadTools Gadgets 
 GadTools Menus          Function Reference 

15 GadTools Library / Elements of GadTools

GadTools is the easy way to program gadgets and menus.  With GadTools, the
system handles the detail work required to control gadgets and menus so
the application uses less code and simpler data structures.

Another key benefit of GadTools is its standardized and elegant look.  All
applications that use GadTools will share a similar appearance and
behavior.  Users will appreciate a sense of instant familiarity even the
first time they use a product.

GadTools provides a significant degree of visual consistency across
multiple applications that use it.  For instance, in Release 2, the
Preferences editors, the Workbench "Information" window and Commodities
Exchange share the same polished look and feel thanks to GadTools.  There
is also internal consistency between different elements of GadTools; the
look is clean and orderly.  Depth is used not just for visual
embellishment, but as an important cue.  For instance, the user is free to
select symbols that appear inside a "raised" area, but "recessed" areas
are informational only, and clicking in them has no effect.

GadTools is not amenable to creative post-processing or hacking by
programmers looking to achieve a result other than what GadTools currently
offers.  Software developers whose needs extend beyond the standard
features of GadTools should create custom gadgets that share the look and
feel of GadTools by using either BOOPSI or by directly programming gadgets
at a lower level.  See the chapters on "Intuition Gadgets" and "BOOPSI"
for more information.  Follow the GadTools rules.  Only in this way may
GadTools grow and improve without hindrance, even allowing new features to
automatically appear in future software when reasonable.

 GadTools Tags 

15 / Elements of GadTools / GadTools Tags

Many of the GadTools functions use TagItem arrays or tag lists to pass
information across the function interface.  These tag-based functions come
in two types, one that takes a pointer to an array of tag items and one
that takes a variable number of tag item arguments directly in the
function call.  In general, the second form, often called the varargs form
because the call takes a variable number of arguments, is provided for
convenience and is internally converted to the first form.  When looking
through the Autodocs or other Amiga reference material, the documentation
for both forms is usually available in the array-based function

All GadTools tags begin with a leading "GT".  In general, they also have a
two-letter mnemonic for the kind of gadget in question.  For example,
slider gadgets recognize tags such as "GTSL_Level".  The GadTools tags are
defined in <libraries/gadtools.h>.  Certain GadTools gadgets also
recognize other Intuition tags such as GA_Disabled and PGA_Freedom, which
can be found in <intuition/gadgetclass.h>.

For more information on tags and tag-based functions, be sure to see the
"Utility Library" chapter in this manual.

15 GadTools Library / GadTools Menus

GadTools menus are easy to use.  Armed only with access to a VisualInfo
data structure, GadTools allows the application to easily create, layout
and delete Intuition menus.

Normally, the greatest difficulty in creating menus is that a large number
of structures must be filled out and linked.  This is bothersome since
much of the required information is orderly and is easier to do
algorithmically than to do manually.  GadTools handles this for you.

There are also many complexities in creating a sensible layout for menus.
This includes some mechanical items such as handling various font sizes,
automatic columnization of menus that are too tall and accounting for
space for checkmarks and Amiga-key equivalents.  There are also aesthetic
considerations, such as how much spacing to provide, where sub-menus
should be placed and so on.

GadTools menu functions support all the features that most applications
will need.  These include:

  * An easily constructed and legible description of the menus.

  * Font-sensitive layout.

  * Support for menus and sub-menus.

  * Sub-menu indicators (a ">>" symbol attached to items with sub-menus).

  * Separator bars for sectioning menus.

  * Command-key equivalents.

  * Checkmarked and mutually exclusive checkmarked menu items.

  * Graphical menu items.

With GadTools, it takes only one structure, the NewMenu structure, to
specifiy the whole menu bar,  For instance, here is how a typical menu
strip containing two menus might be specified:

    struct NewMenu mynewmenu[] =
            { NM_TITLE, "Project",    0 , 0, 0, 0,},
            {  NM_ITEM, "Open...",   "O", 0, 0, 0,},
            {  NM_ITEM, "Save",      "S", 0, 0, 0,},
            {  NM_ITEM, NM_BARLABEL,  0 , 0, 0, 0,},
            {  NM_ITEM, "Print",      0 , 0, 0, 0,},
            {   NM_SUB, "Draft",      0 , 0, 0, 0,},
            {   NM_SUB, "NLQ",        0 , 0, 0, 0,},
            {  NM_ITEM, NM_BARLABEL,  0 , 0, 0, 0,},
            {  NM_ITEM, "Quit...",   "Q", 0, 0, 0,},

            { NM_TITLE, "Edit",       0 , 0, 0, 0,},
            {  NM_ITEM, "Cut",       "X", 0, 0, 0,},
            {  NM_ITEM, "Copy",      "C", 0, 0, 0,},
            {  NM_ITEM, "Paste",     "V", 0, 0, 0,},
            {  NM_ITEM, NM_BARLABEL,  0 , 0, 0, 0,},
            {  NM_ITEM, "Undo",      "Z", 0, 0, 0,},

            {   NM_END, NULL,         0 , 0, 0, 0,},

This NewMenu specification would produce the two menus below:

 Figure 15-1: Two Example Menus  
Figure 15-1: Two Example Menus The NewMenu arrays are designed to be read easily. The elements in the NewMenu array appear in the same order as they will appear on-screen. Unlike the lower-level menu structures described in the "Intuition Menus" chapter earlier, there is no need to specify sub-menus first, then the menu items with their sub-menus, and finally the menu headers with their menu items. The indentation shown above also helps highlight the relationship between menus, menu items and sub-items. The NewMenu Structure GadTools Menus And IntuiMessages GadTools Menus Example Restrictions on GadTools Menus Functions for GadTools Menus Language-Sensitive Menus

15 / GadTools Menus / The NewMenu Structure

The NewMenu structure used to specify GadTools menus is defined in
<libraries/gadtools.h> as follows:

    struct NewMenu
        UBYTE nm_Type;
        STRPTR nm_Label;
        STRPTR nm_CommKey;
        UWORD nm_Flags;
        LONG nm_MutualExclude;
        APTR nm_UserData;

    The first field, nm_Type, defines what this particular NewMenu
    describes.  The defined types provide an unambiguous and convenient
    representation of the application's menus.

        Used to signify a textual menu heading.  Each NM_TITLE signifies
        the start of a new menu within the menu strip.

        Used to signify a textual (NM_ITEM) or graphical (IM_ITEM) menu
        item.  Each NM_ITEM or IM_ITEM becomes a menu item in the
        current menu.

    NM_SUB or IM_SUB
        Used to signify a textual (NM_SUB) or graphical (IM_SUB) menu
        sub-item.  All the consecutive NM_SUBs and IM_SUBs that follow a
        menu item (NM_ITEM or IM_ITEM) compose that item's sub-menu.  A
        subsequent NM_ITEM or IM_ITEM would indicate the start of the
        next item in the original menu, while a subsequent NM_TITLE
        would begin the next menu.

        Used to signify the end of the NewMenu structure array.  The
        last element of the array must have NM_END as its type.

    NM_TITLE, NM_ITEM and NM_SUB are used for textual menu headers, menu
    items and sub-items respectively, in which case nm_Label points to
    the string to be used.  This string is not copied, but rather a
    pointer to it is kept.  Therefore the string must remain valid for
    the active life of the menu.

    Menus don't have to use text, GadTools also supports graphical menu
    items and sub-items (graphical menu headers are not possible since
    they are not supported by Intuition). Simply use IM_ITEM and IM_SUB
    instead and point nm_Label at a valid Image structure.  The Image
    structure can contain just about any graphic image (see the chapter
    on "Intuition Images, Line Drawing and Text" for more on this).

    Sometimes it is a good idea to put a separator between sets of menu
    items or sub-items.  The application may want to separate drastic
    menu items such as "Quit" or "Delete" from more mundane ones.
    Another good idea is to group related checkmarked items by using
    separator bars.

        GadTools will provide a separator bar if the special constant
        NM_BARLABEL is supplied for the nm_Label field of an NM_ITEM or

    A single character string used as the Amiga-key equivalent for the
    menu item or sub-item.

    Menu headers cannot have command keys.  Note that assigning a
    command-key equivalent to a menu item that has sub-items is
    meaningless and should be avoided.

    The nm_CommKey field is a pointer to a string and not a character
    itself.  This was done in part because routines to support different
    languages typically return strings, not characters.  The first
    character of the string is actually copied into the resulting
    MenuItem structure.

    The nm_Flags field of the NewMenu structure corresponds roughly to
    the Flags field of the Intuition's lower-level Menu and MenuItem

    For programmer convenience the sense of the Intuition MENUENABLED and
    ITEMENABLED flags are inverted.  When using GadTools, menus, menu
    items and sub-items are enabled by default.

        To specify a disabled menu, set the NM_MENUDISABLED flag in this

        To disable an item or sub-item, set the NM_ITEMDISABLED flag.

    The Intuition flag bits COMMSEQ (indication of a command-key
    equivalent), ITEMTEXT (indication of a textual or graphical item) and
    HIGHFLAGS (method of highlighting) will be automatically set
    depending on other attributes of the menus.  Do not set these values
    in nm_Flags.

    The nm_Flags field is also used to specify checkmarked menu items.
    To get a checkmark that the user can toggle, set the CHECKIT and
    MENUTOGGLE flags in the nm_Flags field.  Also set the CHECKED flag if
    the item or sub-item is to start in the checked state.

    For specifying mutual exclusion of checkmarked items.  All the items
    or sub-items that are part of a mutually exclusive set should have
    the CHECKIT flag set.

    This field is a bit-wise representation of the items (or sub-items),
    in the same menu or sub-menu, that are excluded by this item (or
    sub-item).  In the simple case of mutual exclusion, where each choice
    excludes all others, set nm_MutualExclude to ~(1<Intuition Menus"
    chapter for more details on menu mutual exclusion.

    The NewMenu structure also has a user data field.  This data is
    stored with the Intuition Menu or MenuItem structures that GadTools
    creates. Use the macros GTMENU_USERDATA(menu) and
    GTMENUITEM_USERDATA(menuitem) defined in <libraries/gadtools.h> to
    extract or change the user data fields of menus and menu items,

    The application may place index numbers in this field and perform a
    switch statement on them, instead of using the Intuition menu
    numbers.  The advantage of this is that the numbers chosen remain
    valid even if the menus are rearranged, while the Intuition menu
    numbers would change when the menus are rearranged.

    Alternately, an efficient technique for menu handling is to create a
    handler function for each menu item and put a pointer to that
    function in the corresponding item's UserData field.  When the
    program receives a IDCMP_MENUPICK message it may call the selected
    item's function through this field.

15 / GadTools Menus / Functions for GadTools Menus

In this section the basic GadTools menu functions are presented.  See the
listing above for an example of how to use these functions.

 Creating Menus         Layout for Individual Menus 
 Layout of the Menus    Freeing Menus 

15 / / Functions for GadTools Menus / Creating Menus

The CreateMenus() function takes an array of NewMenus and creates a set of
initialized and linked Intuition Menu, MenuItem, Image and IntuiText
structures, that need only to be formatted before being used.  Like the
other tag-based functions, there is a CreateMenusA() call that takes a
pointer to an array of TagItems and a CreateMenus() version that expects
to find its tags on the stack.

    struct Menu *CreateMenusA( struct NewMenu *newmenu,
                               struct TagItem *taglist );
    struct Menu *CreateMenus( struct NewMenu *newmenu, Tag tag1, ... );

The first argument to these functions, newmenu, is a pointer to an array
of NewMenu structures as described earlier.  The tag arguments can be any
of the following items:

    The pen number to use for menu text and separator bars.  The default
    is zero.

GTMN_FullMenu (BOOL)
    (New for V37, ignored under V36).  This tag instructs CreateMenus()
    to fail if the supplied NewMenu structure does not describe a
    complete Menu structure.  This is useful if the application does not
    have direct control over the NewMenu description, for example if it
    has user-configurable menus.  The default is FALSE.

GTMN_SecondaryError (ULONG *)
    (New for V37, ignored under V36).  This tag allows CreateMenus() to
    return some secondary error codes.  Supply a pointer to a
    NULL-initialized ULONG, which will receive an appropriate error code
    as follows:

        Invalid menu specification.  For instance, a sub-item directly
        following a menu-title or an incomplete menu.  CreateMenus()
        failed in this case, returning NULL.

        Failed for lack of memory.  CreateMenus() returned NULL.

        The number of menus, items or sub-items exceeded the maximum
        number allowed so the menu was trimmed.  In this case,
        CreateMenus() does not fail but returns a pointer to the trimmed
        Menu structure.

        If no error was detected.

CreateMenus() returns a pointer to the first Menu structure created, while
all the MenuItem structures and any other Menu structures are attached
through the appropriate pointers.  If the NewMenu structure begins with an
entry of type NM_ITEM or IM_ITEM, then CreateMenus() will return a pointer
to the first MenuItem created, since there will be no first Menu
structure.  If the creation fails, usually due to a lack of memory,
CreateMenus() will return NULL.

Starting with V37, GadTools will not create any menus, menu items or
sub-items in excess of the maximum number allowed by Intuition.  Up to 31
menus may be defined, each menu with up to 63 items, each item with up to
31 sub-items.  See the "Intuition Menus" chapter for more information on
menus and their limitations.  If the NewMenu array describes a menu that
is too big, CreateMenus() will return a trimmed version.
GTMN_SecondaryError can be used to learn when this happens.

Menus need to be added to the window with Intuition's SetMenuStrip()
function.  Before doing this, they must be formatted with a call to

15 / / Functions for GadTools Menus / Layout of the Menus

The Menu and MenuItem structures returned by CreateMenus() contain no size
or positional information.  This information is added in a separate layout
step, using LayoutMenus().  As with the other tag-based functions, the
program may call either LayoutMenus() or LayoutMenusA().

    BOOL LayoutMenusA( struct Menu *firstmenu, APTR vi,
                       struct TagItem *taglist );
    BOOL LayoutMenus( struct Menu *firstmenu, APTR vi, Tag tag1, ... );

Set firstmenu to a pointer to a Menu structure returned by a previous call
to CreateMenus().  The vi argument is a a VisualInfo handle obtained from
GetVisualInfo().  See the documentation of GadTools gadgets below for more
about this call.  For the tag arguments, tag1 or taglist, LayoutMenus()
recognizes a single tag:

    A pointer to an openable font (TextAttr structure) to be used for the
    menu item and sub-item text.  The default is to use the screen's font.

LayoutMenus() fills in all the size, font and position information for the
menu strip.  LayoutMenus() returns TRUE if successful and FALSE if it
fails.  The usual reason for failure is that the font supplied cannot be

LayoutMenus() takes care of calculating the width, height and position of
each individual menu item and sub-item, as well as the positioning of all
menus and sub-menus.  In the event that a menu would be too tall for the
screen, it is broken up into multiple columns.  Additionally, whole menus
may be shifted left from their normal position to ensure that they fit on
screen.  If a large menu is combined with a large font, it is possible,
even with columnization and shifting, to create a menu too big for the
screen.  GadTools does not currently trim off excess menus, items or
sub-items, but relies on Intuition to clip menus at the edges of the

It is perfectly acceptable to change the menu layout by calling
ClearMenuStrip() to remove the menus, then LayoutMenus() to make the
change and then SetMenuStrip() to display the new layout.  Do this when
changing the menu's font (this can be handled by a tag to LayoutMenus()),
or when updating the menu's text (to a different language, for instance).
Run-time language switching in menus will be discussed later.

15 / / Functions for GadTools Menus / Layout for Individual Menus

LayoutMenuItems() performs the same function as LayoutMenus(), but only
affects the menu items and sub-items of a single menu instead of the whole
menu strip.  Ordinarily, there is no need to call this function after
having called LayoutMenus().  This function is useful for adding menu
items to an extensible menu, such as the Workbench "Tools" menu.

For example, a single MenuItem can be created by calling CreateMenus()
with a two-entry NewMenu array whose first entry is of type NM_ITEM and
whose second is of type NM_END.  The menu strip may then be removed and
this new item linked to the end of an extensible menu by placing its
address in the NextItem field of the last MenuItem in the menu.
LayoutMenuItems() can then be used to to recalculate the layout of just
the items in the extensible menu and, finally, the menu strip can be
reattached to the window.

    BOOL LayoutMenuItemsA( struct MenuItem *firstitem, APTR vi,
                           struct TagItem *taglist );
    BOOL LayoutMenuItems( struct MenuItem *firstitem, APTR vi,
                          Tag tag1, ... );

Set firstitem to a pointer to the first MenuItem in the linked list of
MenuItems that make up the Menu.  (See the "Intuition Menus" chapter for
more about these structures.)  Set vi to the address of a VisualInfo
handle obtained from GetVisualInfo(). The tag arguments, tag1 or taglist,
may be set as follows:

    A pointer to an openable font (TextAttr structure) to be used for the
    menu item and sub-item text.  The default is to use the screen's font.

    Use this tag to provide a pointer to the Menu structure whose
    FirstItem is passed as the first parameter to this function.  This
    tag should always be used.

LayoutMenuItems() returns TRUE if it succeeds and FALSE otherwise.

15 / / Functions for GadTools Menus / Freeing Menus

The FreeMenus() function frees all the memory allocated by the
corresponding call to CreateMenus().

    void FreeMenus( struct Menu *menu );

Its one argument is the Menu or MenuItem pointer that was returned by
CreateMenus().  It is safe to call FreeMenus() with a NULL parameter,  the
function will then return immediately.

15 / GadTools Menus / GadTools Menus and IntuiMessages

If the window uses GadTools menus and GadTools gadgets, then use the
GT_GetIMsg() and GT_ReplyIMsg() functions described below (or
GT_FilterIMsg() and GT_PostFilterIMsg(), if applicable).  However, if the
window has GadTools menus, but no GadTools gadgets, it is acceptable to
use GetMsg() and ReplyMsg() in the usual manner.

Additionally, no context need be created with CreateContext() if no
GadTools gadgets are used.  For more about these functions, see the
section on "Other GadTools Functions" later in this chapter.

15 / GadTools Menus / Restrictions on GadTools Menus

GadTools menus are regular Intuition menus.  Once the menus have been laid
out, the program may do anything with them, including attaching them or
removing them from windows, enabling or disabling items, checking or
unchecking checkmarked menu items, etc.  See the documentation for
SetMenuStrip(), ClearMenuStrip(), ResetMenuStrip(), OnMenu() and OffMenu()
in the "Intuition Menus" chapter for full details.

If a GadTools-created menu strip is not currently attached to any window,
the program may change the text in the menu headers (Menu->MenuName), the
command-key equivalents (MenuItem->Command) or the text or imagery of menu
items and sub-items, which can be reached as:

    ((struct IntuiText *)MenuItem->ItemFill)->IText
    ((struct Image *)MenuItem->ItemFill)

The application may also link in or unlink menus, menu items or sub-items.
However, do not add sub-items to a menu item that was not created with
sub-items and do not remove all the sub-items from an item that was
created with some.

Any of these changes may be made, provided the program subsequently calls
LayoutMenus() or LayoutMenuItems() as appropriate.  Then, reattach the
menu strip using SetMenuStrip().

Some of these manipulations require walking the menu strip using the usual
Intuition-specified linkages.  Beginning with the first Menu structure,
simply follow its FirstItem pointer to get to the first MenuItem.  The
MenuItem->SubItem pointer will lead to the sub-menus.  MenuItems are
connected via the MenuItem->NextItem field.  Successive menus are linked
together with the Menu->NextMenu pointer.  Again, see the chapter
"Intuition Menus" for details.

15 / GadTools Menus / Language-Sensitive Menus

Allowing the application to switch the language displayed in the menus,
can be done quite easily.  Simply detach the menu strip and replace the
strings in the IntuiText structures as described above.  It may be
convenient to store some kind of index number in the Menu and MenuItem
UserData which can be used to retrieve the appropriate string for the
desired language.  After all the strings have been installed, call
LayoutMenus() and SetMenuStrip().

If the application has the localized strings when the menus are being
created, it simply places the pointers to the strings and command
shortcuts into the appropriate fields of the NewMenu structure.  The menus
may then be processed in the normal way.

15 GadTools Library / GadTools Gadgets

The heart of GadTools is in its ability to easily create and manipulate a
sophisticated and varied array of gadgets.  GadTools supports the
following kinds of gadgets:

  Table 15-1: Standard Gadget Types Supported by the GadTools Library

    Gadget Type         Description or Example Usage
    -----------         ----------------------------
    Button              Familiar action gadgets, such as "OK" or "Cancel".
    String              For text entry.
    Integer             For numeric entry.
    Checkboxes          For on/off items.
    Mutually exclusive  Radio buttons, select one choice among several.
    Cycle               Multiple-choice, pick one of a small number of
    Sliders             To indicate a level within a range.
    Scrollers           To indicate a position in a list or area.
    Listviews           Scrolling lists of text.
    Palette             Color selection.
    Text-display        Read-only text.
    Numeric-display     Read-only numbers.

GadTools gadget handling consists of a body of routines to create, manage
and delete any of the 12 kinds of standard gadgets listed in table 15-1,
such as buttons, sliders, mutually exclusive buttons and scrolling lists.

To illustrate the flexibility, power and simplicity that GadTools offers,
consider the GadTools slider gadget.  This gadget is used to indicate and
control the level of something, for example volume, speed or color
intensity.  Without GadTools, applications have to deal directly with
Intuition proportional and their arcane variables, such as HorizBody to
control the slider knob's size and HorizPot to control the knob's
position.  Using the GadTools slider allows direct specification of the
minimum and maximum levels of the slider, as well as its current level.
For example, a color slider might have a minimum level of 0, a maximum
level of 15 and a current level of 11.

To simplify event-processing for the slider, GadTools only sends the
application a message when the knob has moved far enough to cause the
slider level, as expressed in application terms, to change.  If a user
were to slowly drag the knob of this color slider all the way to the
right, the program will only hear messages for levels 12, 13, 14 and 15,
with an optional additional message when the user releases the

Changing the current level of the slider from within the program is as
simple as specifying the new level in a function call.  For instance, the
application might set the slider's value to 5.

As a final point, the slider is very well-behaved.  When the user releases
the mouse-button, the slider immediately snaps to the centered position
for the level.  If a user sets their background color to light gray, which
might have red = green = blue = 10, all three color sliders will have
their knobs at precisely the same relative position, instead of anywhere
in the range that means "ten".

 The NewGadget Structure 
 Creating Gadgets 
 Handling Gadget Messages 
 IDCMP Flags 
 Freeing Gadgets 
 Simple GadTools Gadget Example 
 Modifying Gadgets 
 The Kinds of GadTools Gadgets 
 Functions for Setting Up GadTools Menus and Gadgets 
 Creating Gadget Lists 
 Gadget Refresh Functions 
 Other GadTools Functions 
 Gadget Keyboard Equivalents 
 Complete GadTools Gadget Example 
 Restrictions on GadTools Gadgets 
 Documented Side-Effects 

15 / GadTools Gadgets / The NewGadget Structure

For most gadgets, the NewGadget structure is used to specify its common
attributes.  Additional attributes that are unique to specific kinds of
gadgets are specified as tags sent to the CreateGadget() function
(described below).

The NewGadget structure is defined in <libraries/gadtools.h> as:

    struct NewGadget
        WORD ng_LeftEdge, ng_TopEdge;
        WORD ng_Width, ng_Height;
        UBYTE *ng_GadgetText;
        struct TextAttr *ng_TextAttr;
        UWORD ng_GadgetID;
        ULONG ng_Flags;
        APTR ng_VisualInfo;
        APTR ng_UserData;

The fields of the NewGadget structure are used as follows:

ng_LeftEdge, ng_TopEdge
    Define the position of the gadget being created.

ng_Width and ng_Height
    Define the size of the gadget being created.

    Most gadgets have an associated label, which might be the text in a
    button or beside a checkmark.  This field contains a pointer to the
    appropriate string.  Note that only the pointer to the text is
    copied, the text itself is not.  The string supplied must remain
    constant and valid for the life of the gadget.

    The application must specify a font to use for the label and any
    other text that may be associated with the gadget.

    Used to describe general aspects of the gadget, which includes where
    the label is to be placed and whether the label should be rendered in
    the highlight color.  The label may be positioned on the left side,
    the right side, centered above, centered below or dead-center on the
    gadget.  For most gadget kinds, the label is placed on the left side
    by default, exceptions will be noted.

ng_GadgetID, ng_UserData
    These user fields are copied into the resulting Gadget structure.

    This field must contain a pointer to an instance of the VisualInfo
    structure, which contains information needed to create and render
    GadTools gadgets.  The VisualInfo structure itself is private to
    GadTools and subject to change.  Use the specialized GadTools
    functions for accessing the VisualInfo pointer, defined below.  Never
    access or modify fields within this structure.

15 / GadTools Gadgets / Creating Gadgets

The main call used to create a gadget with GadTools is CreateGadget().
This function can be used to create a single gadget or it can be called
repeatedly to create a linked list of gadgets.  It takes three arguments
followed by a set of tags:

    struct Gadget *CreateGadget( ULONG kind, struct Gadget *prevgad,
                                 struct NewGadget *newgad,
                                 struct TagItem *taglist)
    struct Gadget *CreateGadgetA(ULONG kind, struct Gadget *prevgad,
                                 struct NewGadget *newgad,
                                 struct Tag tag1, ...)

Set the kind argument to one of the 12 gadget types supported by GadTools.
Set the prevgad argument to the gadget address returned by CreateContext()
if this is the first (or only) gadget in the list.  Subsequent calls to
CreateGadget() can be used to create and link gadgets together in a list
in which case the prevgad argument is set to the address of the gadget
returned by the preceding call to CreateGadget().

Set the newgad argument to the address of the NewGadget structure
describing the gadget to be created and set any special attributes for
this gadget type using the tag arguments, tag1 or taglist.  For instance,
the following code fragment might be used to create the color slider
discussed earlier:

    slidergad = CreateGadget(SLIDER_KIND, newgadget, prevgad,
        GTSL_Min, 0,
        GTSL_Max, 15,
        GTSL_Level, 11,

CreateGadget() typically allocates and initializes all the necessary
Intuition structures, including in this case the Gadget, IntuiText and
PropInfo structures, as well as certain buffers.  For more about these
underlying structures, see the "Intuition Gadgets" chapter.

Since CreateGadget() is a tag-based function, it is easy to add more tags
to get a fancier gadget.  For example, GadTools can optionally display the
running level beside the slider.  The caller must supply a printf()-style
formatting string and the maximum length that the string will resolve to
when the number is inserted:

    slidergad = CreateGadget(SLIDER_KIND, newgadget, prevgad,
        GTSL_Min, 0,
        GTSL_Max, 15,
        GTSL_Level, 11,
        GTSL_LevelFormat, "%2ld" /* printf()-style formatting string */
        GTSL_MaxLevelLen, 2,     /* maximum length of string         */

The level, 0 to 15 in this example, would then be displayed beside the
slider.  The formatting string could instead be "%2ld/15", so the level
would be displayed as "0/15" through "15/15".

15 / GadTools Gadgets / Handling Gadget Messages

GadTools gadgets follow the same input model as other Intuition
components.  When the user operates a GadTools gadget, Intuition notifies
the application about the input event by sending an IntuiMessage.  The
application can get these messages at the Window.UserPort.  However
GadTools gadgets use different message handling functions to get and reply
these messages.  Instead of the Exec functions GetMsg() and ReplyMsg(),
applications should get and reply these messages through a pair of special
GadTools functions, GT_GetIMsg() and GT_ReplyIMsg().

    struct IntuiMessage *GT_GetIMsg(struct MsgPort *iport)
    void  GT_ReplyIMsg(struct IntuiMessage *imsg)

For GT_GetIMsg(), the iport argument should be set to the window's
UserPort.  For GT_ReplyIMsg(), the imsg argument should be set to a
pointer to the IntuiMessage returned by GT_GetIMsg().

These functions ensure that the application only sees the gadget events
that concern it and in a desirable form.  For example, with a GadTools
slider gadget, a message only gets through to the application when the
slider's level actually changes and that level can be found in the
IntuiMessage's Code field:

    imsg = GT_GetIMsg(win->UserPort);
    object = imsg->IAddress;
    class = imsg->Class;
    code = imsg->Code;
    switch (class)
        case IDCMP_MOUSEMOVE:
            if (object == slidergad)
                printf("Slider at level %ld\n", code);

In general, the IntuiMessages received from GadTools contain more
information in the Code field than is found in regular Intuition gadget
messages.  Also, when dealing with GadTools a lot of messages (mostly
IDCMP_MOUSEMOVEs) do not have to be processed by the application.  These
are two reasons why dealing with GadTools gadgets is much easier than
dealing with regular Intuition gadgets.  Unfortunately this processing
cannot happen magically, so applications must use GT_GetIMsg() and
GT_ReplyIMsg() where they would normally have used GetMsg() and ReplyMsg().

GT_GetIMsg() actually calls GetMsg() to remove a message from the
specified window's UserPort.  If the message pertains to a GadTools gadget
then some dispatching code in GadTools will be called to process the
message.  What the program will receive from GT_GetIMsg() is actually a
copy of the real IntuiMessage, possibly with some supplementary
information from GadTools, such as the information typically found in the
Code field.

The GT_ReplyIMsg() call will take care of cleaning up and replying to the
real IntuiMessage.

    When an IDCMP_MOUSEMOVE message is received from a GadTools gadget,
    GadTools arranges to have the gadget's pointer in the IAddress
    field of the IntuiMessage.  While this is extremely convenient, it
    is also untrue of messages from regular Intuition gadgets (described
    in the "Intuition Gadgets" chapter).  Do not make the mistake of
    assuming it to be true.

This description of the inner workings of GT_GetIMsg() and GT_ReplyIMsg()
is provided for understanding only; it is crucial that the program make no
assumptions or interpretations about the real IntuiMessage.  Any such
inferences are not likely to hold true in the future.  See the section on
documented side-effects for more information.

15 / GadTools Gadgets / IDCMP Flags

The various GadTools gadget types require certain classes of IDCMP
messages in order to work.  Applications specify these IDCMP classes when
the window is opened or later with ModifyIDCMP() (see "Intuition Windows"
chapter for more on this).  Each kind of GadTools gadget requires
one or more of these IDCMP classes: IDCMP_GADGETUP, IDCMP_GADGETDOWN,
convenience, the IDCMP classes required by each kind of gadget are defined
in <libraries/gadtools.h>.  For example, SLIDERIDCMP is defined to be:


    Always OR the IDCMP Flag Bits.
    When specifying the IDCMP classes for a window, never add the
    flags together, always OR the bits together.  Since many of the
    GadTools IDCMP constants have multiple bits set, adding the values
    will not lead to the proper flag combination.

If a certain kind of GadTools gadget is used, the window must use all
IDCMP classes required by that kind of gadget.  Do not omit any that are
given for that class, even if the application does require the message

Because of the way GadTools gadgets are implemented, programs that use
them always require notification about window refresh events.  Even if the
application performs no rendering of its own, it may not use the
WFLG_NOCAREREFRESH window flag and must always set IDCMP_REFRESHWINDOW.
See the section on "Gadget Refresh Functions" later in this chapter for
more on this.

15 / GadTools Gadgets / Freeing Gadgets

After closing the window, the gadgets allocated using CreateGadget() must
be released.  FreeGadgets() is a simple call that will free all the
GadTools gadgets that it finds, beginning with the gadget whose pointer is
passed as an argument.

    void FreeGadgets( struct Gadget *gad );

The gad argument is a pointer to the first gadget to be freed.  It is safe
to call FreeGadgets() with a NULL gadget pointer, the function will then
return immediately.  Before calling FreeGadgets(), the application must
first either remove the gadgets or close the window.

When the gadget passed to FreeGadgets() is the first gadget in a linked
list, the function frees all the GadTools gadgets on the list without
patching pointers or trying to maintain the integrity of the list.  Any
non-GadTools gadgets found on the list will not be freed, hence the result
will not necessarily form a nice list since any intervening GadTools
gadgets will be gone.

See the section on "Creating Gadget Lists" for more information on using
linked lists of gadgets.

15 / GadTools Gadgets / Modifying Gadgets

The attributes of a gadget are set up when the gadget is created.  Some of
these attributes can be changed later by using the GT_SetGadgetAttrs()

    void GT_SetGadgetAttrs (struct Gadget *gad, struct Window *win,
                            struct Requester *req, Tag tag1, ... )
    void GT_SetGadgetAttrsA(struct Gadget *gad, struct Window *win,
                            struct Requester *req, struct TagItem *taglist)

The gad argument specifies the gadget to be changed while the win argument
specifies the window the gadget is in.  Currently, the req argument is
unused and must be set to NULL.

The gadget attributes are changed by passing tag arguments to these
functions.  The tag arguments can be either a set of TagItems on the stack
for GT_SetGadgetAttrs(), or a pointer to an array of TagItems for
GT_SetGadgetAttrsA().  The tag items specify the attributes that are to be
changed for the gadget.  Keep in mind though that not every gadget
attribute can be modified this way.

For example, in the slider gadget presented earlier, the level-formatting
string may not be changed after the gadget is created.  However, the
slider's level may be changed to 5 as follows:

    GT_SetGadgetAttrs(slidergad, win, req,
        GTSL_Level, 5,

Here are some other example uses of GT_SetGadgetAttrs() to change gadget
attributes after it is created.

    /* Disable a button gadget */
    GT_SetGadgetAttrs(buttongad, win, NULL,
                            GA_Disabled, TRUE,

    /* Change a slider's range to be 1 to 100, currently at 50 */
    GT_SetGadgetAttrs(slidergad, win, NULL,
                            GTSL_Min, 1,
                            GTSL_Max, 100,
                            GTSL_Level, 50,

    /* Add a node to the head of listview's list, and make it */
    /* the selected one */
    GT_SetGadgetAttrs(listviewgad, win, NULL,
                            /* detach list before modifying */
                            GTLV_Labels, ~0,
    AddHead(&lvlabels, &newnode);
    GT_SetGadgetAttrs(listviewgad, win, NULL,
                            /* re-attach list */
                            GTLV_Labels, &lvlabels,
                            GTLV_Selected, 0,

When changing a gadget using these functions, the gadget will
automatically update its visuals.  No refresh is required, nor should any
refresh call be performed.

    The GT_SetGadgetAttrs() functions may not be called inside of a
    GT_BeginRefresh()/GT_EndRefresh() pair.  This is true of Intuition
    gadget functions generally, including those discussed in the
    "Intuition Gadgets" chapter.

In the sections that follow all the possible attributes for each kind of
gadget are discussed.  The tags are also described in the Autodocs for
GT_SetGadgetAttrs() in the Amiga ROM Kernel Reference Manual: Includes and

    Tags that can only be sent to CreateGadget() and not to
    GT_SetGadgetAttrs() will be marked as create only in the
    discussion that follows.  Those that are valid parameters to both
    functions will be marked as create and set.

15 / GadTools Gadgets / The Kinds of GadTools Gadgets

This section discusses the unique features of each kind of gadget
supported by the GadTools library.

 Button Gadgets 
 Text-Entry and Number-Entry Gadgets 
 Checkbox Gadgets 
 Mutually-Exclusive Gadgets 
 Cycle Gadgets 
 Slider Gadgets 
 Scroller Gadgets 
 Listview Gadgets 
 Palette Gadgets 
 Text-Display and Numeric-Display Gadgets 
 Generic Gadgets 

15 / / The Kinds of GadTools Gadgets / Button Gadgets

Button gadgets (BUTTON_KIND) are perhaps the simplest kind of GadTools
gadget.  Button gadgets may be used for objects like the "OK" and "Cancel"
buttons in requesters.  GadTools will create a hit-select button with a
raised bevelled border.  The label supplied will be centered on the
button's face.  Since the label is not clipped, be sure that the gadget is
large enough to contain the text supplied.

Button gadgets recognize only one tag:

GA_Disabled (BOOL)
    Set this attribute to TRUE to disable or ghost the button gadget, to
    FALSE otherwise.  The default is FALSE. (Create and set.)

When the user selects a button gadget, the program will receive an

If clicking on a button causes a requester to appear, for example a button
that brings up a color requester, then the button text should end in
ellipsis (...), as in "Quit..."

15 / / Kinds of GadTools Gadgets / Text-Entry and Number-Entry Gadgets

Text-entry (STRING_KIND) and number-entry (INTEGER_KIND) gadgets are
fairly typical Intuition string gadgets.  The typing area is contained by
a border which is a raised ridge.

Text-entry gadgets accept the following tags:

    A pointer to the string to be placed into the text-entry gadget
    buffer or NULL to get an empty text-entry gadget.  The string itself
    is actually copied into the gadget's buffer.  The default is NULL.
    (Create and set.)

    The maximum number of characters that the text-entry gadget should
    hold.  The string buffer that gets created for the gadget will
    actually be one bigger than this number, in order to hold the
    trailing NULL.  The default is 64.  (Create only.)

Number-entry gadgets accept the following tags:

    The number to be placed into the number-entry gadget.  The default is
    zero. (Create and set.)

    The maximum number of digits that the number-entry gadget should
    hold.  The string buffer that gets created for the gadget will
    actually be one bigger than this, in order to hold the trailing NULL.
    The default is 10. (Create only.)

Both text-entry and number-entry gadgets, which are collectively called
string gadgets, accept these common tags:

    This attribute controls the placement of the string or number within
    its box and can be one of GACT_STRINGLEFT, GACT_STRINGRIGHT or
    GACT_STRINGCENTER.  The default is GACT_STRINGLEFT.  (Create only.)

STRINGA_ReplaceMode (BOOL)
    Set STRINGA_ReplaceMode to TRUE to get a string gadget which is in
    replace-mode, as opposed to auto-insert mode.  (Create only.)

GA_Disabled (BOOL)
    Set this attribute to TRUE to disable the string gadget, otherwise to
    FALSE.  The default is FALSE.  (Create and set.)

    (New for V37, ignored under V36).  Set this attribute to TRUE if the
    application wants to hear the Help key from within this string
    gadget.  This feature allows the program to hear the press of the
    Help key in all cases.  If TRUE, pressing the help key while this
    gadget is active will terminate the gadget and send a message.  The
    program will receive an IDCMP_GADGETUP message having a Code value of
    0x5F, the rawkey code for Help.  Typically, the program will want to
    reactivate the gadget after performing the help-display.  The default
    is FALSE.  (Create only.)

GA_TabCycle (BOOL)
    (New for V37, ignored under V36).  If the user types Tab or Shift Tab
    into a GA_TabCycle gadget, Intuition will activate the next or
    previous such gadget in sequence.  This gives the user easy keyboard
    control over which text-entry or number-entry gadget is active.  Tab
    moves to the next GA_TabCycle gadget in the gadget list and Shift Tab
    moves to the previous one.  When the user presses Tab or Shift Tab,
    Intuition will deactivate the gadget and send this program an
    IDCMP_GADGETUP message with the code field set to 0x09, the ASCII
    value for a tab.  Intuition will then activate the next indicated
    gadget.  Check the shift bits of the qualifier field to learn if
    Shift Tab was typed.  The ordering of the gadgets may only be
    controlled by the order in which they were added to the window.  For
    special cases, for example, if there is only one string gadget in the
    window, this feature can be suppressed by specifying the tagitem pair
    {GA_TabCycle, FALSE}.  The default is TRUE.  (Create only.)

GTST_EditHook (struct Hook *)
    (New for V37, ignored under V36).  Pointer to a custom editing hook
    for this string or integer gadget.  See the "Intuition Gadgets"
    chapter for more information on string gadget edit-hooks.

As with all Intuition string gadgets, the program will receive an
IDCMP_GADGETUP message only when the user presses Enter, Return, Help, Tab
or Shift Tab while typing in the gadget.  Note that, like Intuition string
gadgets, the program will not hear anything if the user deactivates the
string gadget by clicking elsewhere.  Therefore, it is a good idea to
always check the string gadget's buffer before using its contents, instead
of just tracking its value as IDCMP_GADGETUP messages are received for
this gadget.

Be sure the code is designed so that nothing drastic happens, like closing
a requester or opening a file, if the IDCMP_GADGETUP message has a
non-zero Code field; the program will want to handle the Tab and Help
cases intelligently.

To read the string gadget's buffer, look at the Gadget's StringInfo Buffer:

    ((struct StringInfo *)gad->SpecialInfo)->Buffer

To determine the value of an integer gadget, look at the Gadget's
StringInfo LongInt in the same way.

Always use the GTST_String or GTIN_Number tags to set these values.  Never
write to the StringInfo->Buffer or StringInfo->LongInt fields directly.

GadTools string and integer gadgets do not directly support the
GA_Immediate property (which would cause Intuition to send an
IDCMP_GADGETDOWN event when such a gadget is first selected).  However,
this property can be very important.  Therefore, the following technique
can be used to enable this property.

    Note that the technique shown here relies on directly setting flags
    in a GadTools gadget; this is not normally allowed since it hinders
    future compatibility.  Do not attempt to change other flags or
    properties of GadTools gadgets except through the defined interfaces
    of CreateGadgetA() and GT_SetGadgetAttrsA().  Directly modifying
    flags or properties is legal only when officially sanctioned by

To get the GA_Immediate property, pass the {GA_Immediate,TRUE} tag to
CreateGadgetA().  Even though this tag is ignored for string and integer
gadgets under V37, this will allow future versions of GadTools to learn of
your request in the correct way.  Then, under V37 only, set the
GACT_IMMEDIATE flag in the gadget's Activation field:

    gad = CreateGadget( STRING_KIND, gad, &ng,
            /* string gadget tags go here */

            /* Add this tag for future GadTools releases */
            GA_Immediate, TRUE,
            TAG_DONE );

    if ( ( gad ) && ( GadToolsBase->lib_Version == 37) )
            /* Under GadTools V37 only, set this attribute
             * directly.  Do not set this attribute under
             * future versions of GadTools, or for gadgets
             * other than STRING_KIND or INTEGER_KIND.
            gad->Activation |= GACT_IMMEDIATE;

15 / / The Kinds of GadTools Gadgets / Checkbox Gadgets

Checkboxes (CHECKBOX_KIND) are appropriate for presenting options which
may be turned on or off.  This kind of gadget consists of a raised box
which contains a checkmark if the option is selected or is blank if the
option is not selected.  Clicking on the box toggles the state of the

The width and height of a checkbox are currently fixed (to 26x11). If
variable-sized checkboxes are added in the future,  they will be done in a
compatible manner.  Currently the width and height specified in the
NewGadget structure are ignored.

The checkbox may be controlled with the following tags:

GTCB_Checked (BOOL)
    Set this attribute to TRUE to set the gadget's state to checked.  Set
    it to FALSE to mark the gadget as unchecked.  The default is FALSE.
    (Create and set.)

GA_Disabled (BOOL)
    Set this attribute to TRUE to disable the checkbox, to FALSE
    otherwise.  The default is FALSE.  (Create and set.)

When the user selects a checkbox, the program will receive an IntuiMessage
with a class of IDCMP_GADGETUP.  As this gadget always toggles, the
program can easily track the state of the gadget.  Feel free to read the
Gadget->Flags GFLG_SELECTED bit.  Note, however, that the Gadget structure
itself is not synchronized to the IntuiMessages received.  If the user
clicks a second time, the GFLG_SELECTED bit can toggle again before the
program gets a chance to read it.  This is true of any of the dynamic
fields of the Gadget structure, and is worth being aware of, although only
rarely will an application have to account for it.

15 / / The Kinds of GadTools Gadgets / Mutually-Exclusive Gadgets

Use mutually exclusive gadgets (MX_KIND), or radio buttons, when the user
must choose only one option from a short list of possibilities.  Mutually
exclusive gadgets are appropriate when there are a small number of
choices, perhaps eight or less.

A set of mutually exclusive gadgets consists of a list of labels and
beside each label, a small raised oval that looks like a button.  Exactly
one of the ovals is recessed and highlighted, to indicate the selected
choice.  The user can pick another choice by clicking on any of the raised
ovals.  This choice will become active and the previously selected choice
will become inactive.  That is, the selected oval will become recessed
while the previous one will pop out, like the buttons on a car radio.

Mutually exclusive gadgets recognize these tags:

GTMX_Labels (STRPTR *)
    A NULL-pointer-terminated array of strings which are to be the labels
    beside each choice in the set of mutually exclusive gadgets.  This
    array determines how many buttons are created.  This array must be
    supplied to CreateGadget() and may not be changed.  The strings
    themselves must remain valid for the lifetime of the gadget.  (Create

    The ordinal number, counting from zero, of the active choice of the
    set of mutually exclusive gadgets.  The default is zero.  (Create and

GTMX_Spacing (UWORD)
    The amount of space, in pixels, that will be placed between
    successive choices in a set of mutually exclusive gadgets.  The
    default is one.  (Create only.)

When the user selects a new choice from a set of mutually exclusive
gadgets, the program will receive an IDCMP_GADGETDOWN IntuiMessage. Look
in the IntuiMessage's Code field for the ordinal number of the new active

The ng_GadgetText field of the NewGadget structure is ignored for mutually
exclusive gadgets.  The text position specified in ng_Flags  determines
whether the item labels are placed to the left or the right of the radio
buttons themselves.  By default, the labels appear on the left.  Do not

Like the checkbox, the size of the radio button is currently fixed, and
the dimensions supplied in the NewGadget structure are ignored.  If in the
future the buttons are made scalable, it will be done in a compatible
manner.  Currently, mutually exclusive gadgets may not be disabled.

15 / / The Kinds of GadTools Gadgets / Cycle Gadgets

Like mutually exclusive gadgets, cycle gadgets (CYCLE_KIND) allow the user
to choose exactly one option from among several.

The cycle gadget appears as a raised rectangular button with a vertical
divider near the left side.  A circular arrow glyph appears to the left of
the divider, while the current choice appears to the right.  Clicking on
the cycle gadget advances to the next choice, while shift-clicking on it
changes it to the previous choice.

Cycle gadgets are more compact than mutually exclusive gadgets, since only
the current choice is displayed.  They are preferable to mutually
exclusive gadgets when a window needs to have several such gadgets as in
the PrinterGfx Preferences editor, or when there is a medium number of
choices.  If the number of choices is much more than about a dozen, it may
become too frustrating and inefficient for the user to find the desired
choice.  In that case, use a listview (scrolling list) instead.

The tags recognized by cycle gadgets are:

GTCY_Labels (STRPTR *)
    Like GTMX_Labels, this tag is associated with a
    NULL-pointer-terminated array of strings which are the choices that
    this gadget allows.  This array must be supplied to CreateGadget(),
    and can only be changed starting in V37.  The strings themselves must
    remain valid for the lifetime of the gadget.  (Create only (V36),
    Create and set (V37).)

    The ordinal number, counting from zero, of the active choice of the
    cycle gadget.  The default is zero.  (Create and set.)

GA_Disabled (BOOL)
    (New for V37, ignored by V36.)  Set this attribute to TRUE to disable
    the cycle gadget, to FALSE otherwise.  The default is FALSE.  (Create
    and set.)

When the user clicks or shift-clicks on a cycle gadget, the program will
receive an IDCMP_GADGETUP IntuiMessage.  Look in the Code field of the
IntuiMessage for the ordinal number of the new active selection.

15 / / The Kinds of GadTools Gadgets / Slider Gadgets

Sliders are one of the two kinds of proportional gadgets offered by
GadTools.  Slider gadgets (SLIDER_KIND) are used to control an amount, a
level or an intensity, such as volume or color.  Scroller gadgets
(SCROLLER_KIND) are discussed below.

Slider gadgets accept the following tags:

    The minimum level of a slider.  The default is zero.  (Create and

    The maximum level of a slider.  The default is 15.  (Create and set.)

    The current level of a slider. The default is zero. When the level is
    at its minimum, the knob will be all the way to the left for a
    horizontal slider or all the way at the bottom for a vertical slider.
    Conversely, the maximum level corresponds to the knob being to the
    extreme right or top.  (Create and set.)

GTSL_LevelFormat (STRPTR)
    The current level of the slider may be displayed in real-time
    alongside the gadget.  To use the level-display feature, the program
    must be using a monospace font for this gadget.

    GTSL_LevelFormat specifies a printf()-style formatting string used to
    render the slider level beside the slider (the complete set of
    formatting options is described in the Exec library function
    RawDoFmt()).  Be sure to use the `l' (long word) modifier for the
    number.  Field-width specifiers may be used to ensure that the
    resulting string is always of constant width.  The simplest would be
    "%2ld".  A 2-digit hexadecimal slider might use "%02lx", which adds
    leading zeros to the number.  Strings with extra text, such as "%3ld
    hours", are permissible.  If this tag is specified, the program must
    also provide GTSL_MaxLevelLen.  By default, the level is not
    displayed.  (Create only.)

GTSL_MaxLevelLen (UWORD)
    The maximum length of the string that will result from the given
    level-formatting string.  If this tag is specified, the program must
    also provide GTSL_LevelFormat.  By default, the level is not
    displayed.  (Create only.)

    To choose where the optional display of the level is positioned.  It
    PLACETEXT_BELOW.  The level may be placed anywhere with the following
    exception: the level and the label may not be both above or both
    below the gadget.  To place them both on the same side, allow space
    in the gadget's label (see the example).  The default is
    PLACETEXT_LEFT.  (Create only.)

GTSL_DispFunc (LONG (*function)(struct Gadget *, WORD))
    Optional function to convert the level for display.  A slider to
    select the number of colors for a screen may operate in screen depth
    (1 to 5, for instance), but actually display the number of colors (2,
    4, 8, 16 or 32).  This may be done by providing a GTSL_DispFunc
    function which returns 1 << level.  The function must take a pointer
    to the Gadget as the first parameter and the level, a WORD, as the
    second and return the result as a LONG.  The default behavior for
    displaying a level is to do so without any conversion.  (Create only.)

GA_Immediate (BOOL)
    Set this to TRUE to receive an IDCMP_GADGETDOWN IntuiMessage when the
    user presses the mouse button over the slider.  The default is FALSE.
    (Create only.)

GA_RelVerify (BOOL)
    Set this to TRUE to receive an IDCMP_GADGETUP IntuiMessage when the
    user releases the mouse button after using the slider.  The default
    is FALSE.  (Create only.)

    Specifies which direction the knob may move.  Set to LORIENT_VERT for
    a vertical slider or LORIENT_HORIZ for a horizontal slider.  The
    default is LORIENT_HORIZ.  (Create only.)

GA_Disabled (BOOL)
    Set this attribute to TRUE to disable the slider, to FALSE otherwise.
    The default is FALSE.  (Create and set.)

Up to three different classes of IntuiMessage may be received at the port
when the user plays with a slider, these are IDCMP_MOUSEMOVE,
IDCMP_GADGETUP and IDCMP_GADGETDOWN.  The program may examine the
IntuiMessage Code field to discover the slider's level.

IDCMP_MOUSEMOVE IntuiMessages will be heard whenever the slider's level
changes.  IDCMP_MOUSEMOVE IntuiMessages will not be heard if the knob has
not moved far enough for the level to actually change.  For example if the
slider runs from 0 to 15 and is currently set to 12, if the user drags the
slider all the way up the program will hear no more than three
IDCMP_MOUSEMOVEs, one each for 13, 14 and 15.

If {GA_Immediate, TRUE} is specified, then the program will always hear an
IDCMP_GADGETDOWN IntuiMessage when the user begins to adjust a slider.  If
{GA_RelVerify, TRUE} is specified, then the program will always hear an
IDCMP_GADGETUP IntuiMessage when the user finishes adjusting the slider.
If IDCMP_GADGETUP or IDCMP_GADGETDOWN IntuiMessages are requested, the
program will always hear them, even if the level has not changed since the
previous IntuiMessage.

Note that the Code field of the IntuiMessage structure is a UWORD, while
the slider's level may be negative, since it is a WORD.  Be sure to copy
or cast the IntuiMessage->Code into a WORD if the slider has negative

If the user clicks in the container next to the knob, the slider level
will increase or decrease by one.  If the user drags the knob itself, then
the knob will snap to the nearest integral position when it is released.

Here is an example of the screen-depth slider discussed earlier:

    /* NewGadget initialized here. Note the three spaces
     * after "Slider:", to allow a blank plus the two digits
     * of the level display
    ng.ng_Flags = PLACETEXT_LEFT;
    ng.ng_GadgetText = "Slider:   ";

    LONG DepthToColors(struct Gadget *gad, WORD level)
    return ((WORD)(1 << level));


    gad = CreateGadget(SLIDER_KIND, gad, &ng,
        GTSL_Min, 1,
        GTSL_Max, 5,
        GTSL_Level, current_depth,
        GTSL_MaxLevelLen, 2,
        GTSL_LevelFormat, "%2ld",
        GTSL_DispFunc, DepthToColors,

15 / / The Kinds of GadTools Gadgets / Scroller Gadgets

Scrollers (SCROLLER_KIND) bear some similarity to sliders, but are used
for a quite different job: they allow the user to adjust the position of a
limited view into a larger area.  For example, Workbench's windows have
scrollers that allow the user to see icons that are outside the visible
portion of a window.  Another example is a scrolling list in a file
requester which has a scroller that allows the user to see different parts
of the whole list.

A scroller consists of a proportional gadget and usually also has a pair
of arrow buttons.

While the slider deals in minimum, maximum and current level, the scroller
understands Total, Visible and Top.  For a scrolling list, Total would be
the number of items in the entire list, Visible would be the number of
lines visible in the display area and Top would be the number of the first
line displayed in the visible part of the list.  Top would run from zero
to Total - Visible.  For an area-scroller such as those in Workbench's
windows, Total would be the height (or width) of the whole area, Visible
would be the visible height (or width) and Top would be the top (or left)
edge of the visible part.

Note that the position of a scroller should always represent the position
of the visible part of the project and never the position of a cursor or
insertion point.

Scrollers respect the following tags:

    The top line or position visible in the area that the scroller
    represents.  The default is zero.  (Create and set.)

    The total number of lines or positions that the scroller represents.
    The default is zero.  (Create and set.)

GTSC_Visible (WORD)
    The visible number of lines or positions that the scroller
    represents.  The default is two.  (Create and set.)

    Asks for arrow gadgets to be attached to the scroller.  The value
    supplied will be used as the width of each arrow button for a
    horizontal scroller or the height of each arrow button for a vertical
    scroller, the other dimension will be set by GadTools to match the
    scroller size.  It is generally recommend that arrows be provided.
    The default is no arrows.  (Create only.)

GA_Immediate (BOOL)
    Set this to TRUE to receive an IDCMP_GADGETDOWN IntuiMessage when the
    user presses the mouse button over the scroller.  The default is
    FALSE.  (Create only.)

GA_RelVerify (BOOL)
    Set this to TRUE to receive an IDCMP_GADGETUP IntuiMessage when the
    user releases the mouse button after using the scroller.  The default
    is FALSE.  (Create only.)

    Specifies which direction the knob may move.  Set to LORIENT_VERT for
    a vertical scroller or LORIENT_HORIZ for a horizontal scroller.  The
    default is LORIENT_HORIZ.  (Create only.)

GA_Disabled (BOOL)
    Set this attribute to TRUE to disable the scroller, to FALSE
    otherwise.  The default is FALSE.  (Create and set.)

The IntuiMessages received for a scroller gadget are the same in nature as
those for a slider defined above, including the fact that messages are
only heard by the program when the knob moves far enough for the Top value
to actually change. The Code field of the IntuiMessage will contain the
new Top value of the scroller.

If the user clicks on an arrow gadget, the scroller moves by one unit.  If
the user holds the button down over an arrow gadget, it repeats.

If the user clicks in the container next to the knob, the scroller will
move by one page, which is the visible amount less one.  This means that
when the user pages through a scrolling list, any pair of successive views
will overlap by one line.  This helps the user understand the continuity
of the list.  If the program is using a scroller to pan through an area
then there will be an overlap of one unit between successive views.  It is
recommended that Top, Visible and Total be scaled so that one unit
represents about five to ten percent of the visible amount.

15 / / The Kinds of GadTools Gadgets / Listview Gadgets

Listview gadgets (LISTVIEW_KIND) are scrolling lists.  They consist of a
scroller with arrows, an area where the list itself is visible and
optionally a place where the current selection is displayed, which may be
editable.  The user can browse through the list using the scroller or its
arrows and may select an entry by clicking on that item.

There are a number of tags that are used with listviews:

GTLV_Labels (struct List *)
    An Exec list whose nodes' ln_Name fields are to be displayed as items
    in the scrolling list.  If the list is empty, an empty List structure
    or a NULL value may be used for GTLV_Labels.  This tag accepts a
    value of "~0" to detach the list from the listview, defined below.
    The default is NULL.  (Create and set.)

    The ordinal number of the top item visible in the listview.  The
    default is zero.  (Create and set.)

GTLV_ReadOnly (BOOL)
    Set this to TRUE for a read-only listview, which the user can browse,
    but not select items from.  A read-only listview can be recognized
    because the list area is recessed, not raised.  The default is FALSE.
    (Create only.)

GTLV_ScrollWidth (UWORD)
    The width of the scroller to be used in the listview.  Any value
    specified must be reasonably bigger than zero.  The default is 16.
    (Create only.)

GTLV_ShowSelected (struct Gadget *)
    Use this tag to show the currently selected entry displayed
    underneath the listview.  Set its value to NULL to get a read-only
    (TEXT_KIND) display of the currently selected entry or set it to a
    pointer to an already-created GadTools STRING_KIND gadget to allow
    the user to directly edit the current entry.  By default, there is no
    display of the currently selected entry.  (Create only.)

GTLV_Selected (UWORD)
    Ordinal number of the item to be placed into the display of the
    current selection under the listview.  This tag is ignored if
    GTLV_ShowSelected is not used.  Set it to "~0" to have no current
    selection.  The default is "~0".  (Create and set.)

    Extra space, in pixels, to be placed between the entries in the
    listview.  The default is zero.  (Create only.)

The program will only hear from a listview when the user selects an item
from the list.  The program will then receive an IDCMP_GADGETUP
IntuiMessage.  This message will contain the ordinal number of the item
within the list that was selected in the Code field of the message.  This
number is independent of the displayed listview, it is the offset from the
start of the list of items.

If the program attaches a display gadget by using the TagItem
{GTLV_ShowSelected, NULL}, then whenever the user clicks on an entry in
the listview it will be copied into the display gadget.

If the display gadget is to be editable, then the program must first
create a GadTools STRING_KIND gadget whose width matches the width of the
listview.  The TagItem {GTLV_ShowSelected, stringgad} is used to install
the editable gadget, where stringgad is the pointer returned by
CreateGadget().  When the user selects any entry from the listview, it
gets copied into the string gadget.  The user can edit the string and the
program will hear normal string gadget IDCMP_GADGETUP messages from the

The Exec List and its Node structures may not be modified while they are
attached to the listview, since the list might be needed at any time.  If
the program has prepared an entire new list, including a new List
structure and all new nodes, it may replace the currently displayed list
in a single step by calling GT_SetGadgetAttrs() with the TagItem
{GTLV_Labels, newlist}.  If the program needs to operate on the list that
has already been passed to the listview, it should detach the list by
setting the GTLV_Labels attribute to "~0".  When done modifying the list,
resubmit it by setting GTLV_Labels to once again point to it.  This is
better than first setting the labels to NULL and later back to the list,
since setting GTLV_Labels to NULL will visually clear the listview.  If
the GTLV_Labels attribute is set to "~0", the program is expected to set
it back to something determinate, either a list or NULL, soon after.

The height specified for the listview will determine the number of lines
in the list area.  When creating a listview, it will be no bigger than the
size specified in the NewGadget structure.  The size will include the
current-display gadget, if any, that has been requested via the
GTLV_ShowSelected tag.  The listview may end up being less tall than the
application asked for, since the calculated height assumes an integral
number of lines in the list area.

By default, the gadget label will be placed above the listview.  This may
be overridden using ng_Flags.

Currently, a listview may not be disabled.

15 / / The Kinds of GadTools Gadgets / Palette Gadgets

Palette gadgets (PALETTE_KIND) let the user pick a color from a set of
several.  A palette gadget consists of a number of colored squares, one
for each color available.  There may also be an optional indicator square
which is filled with the currently selected color.  To create a color
editor, a palette gadget would be combined with some sliders to control
red, green and blue components, for example.

Palette gadgets use the following tags:

    The number of bitplanes that the palette represents.  There will be 1
    << depth squares in the palette gadget.  The default is one.  (Create

    The selected color of the palette.  The default is one.  (Create and

GTPA_ColorOffset (UBYTE)
    The first color to use in the palette.  For example, if GTPA_Depth is
    two and GTPA_ColorOffset is four, then the palette will have squares
    for colors four, five, six and seven.  The default is zero.  (Create

GTPA_IndicatorWidth (UWORD)
    The desired width of the current-color indicator.  By specifying this
    tag, the application is asking for an indicator to be placed to the
    left of the color selection squares.  The indicator will be as tall
    as the gadget itself.  By default there is no indicator.  (Create

GTPA_IndicatorHeight (UWORD)
    The desired height of the current-color indicator.  By specifying
    this tag, the application is asking for an indicator to be placed
    above the color selection squares.  The indicator will be as wide as
    the gadget itself.  By default there is no indicator.  (Create only.)

GA_Disabled (BOOL)
    Set this attribute to TRUE to disable the palette gadget, to FALSE
    otherwise.  The default is FALSE.  (Create and set.)

An IDCMP_GADGETUP IntuiMessage will be received when the user selects a
color from the palette.  The current-color indicator is recessed,
indicating that clicking on it has no effect.

If the palette is wide and not tall, use the GTPA_IndicatorWidth tag to
put the indicator on the left.  If the palette is tall and narrow, put the
indicator on top using GTPA_IndicatorHeight.

By default, the gadget's label will go above the palette gadget, unless
GTPA_IndicatorWidth is specified, in which case the label will go on the
left.  In either case, the default may be overridden by setting the
appropriate flag in the NewGadget's ng_Flags field.

The size specified for the palette gadget will determine how the area is
subdivided to make the individual color squares.  The actual size of the
palette gadget will be no bigger than the size given, but it can be
smaller in order to make the color squares all exactly the same size.

15 / / Kinds of GadTools / Text-Display and Numeric-Display Gadgets

Text-display (TEXT_KIND) and numeric-display (NUMBER_KIND) gadgets are
read-only displays of information.  They are useful for displaying
information that is not editable or selectable, while allowing the
application to use the GadTools formatting and visuals.  Conveniently, the
visuals are automatically refreshed through normal GadTools gadget
processing.  The values displayed may be modified by the program in the
same way other GadTools gadgets may be updated.

Text-display and number-display gadgets consist of a fixed label (the one
supplied as the NewGadget's ng_GadgetText), as well as a changeable string
or number (GTTX_Text or GTNM_Number respectively).  The fixed label is
placed according to the PLACETEXT_ flag chosen in the NewGadget ng_Flags
field.  The variable part is aligned to the left-edge of the gadget.

Text-display gadgets recognize the following tags:

    Pointer to the string to be displayed or NULL for no string.  The
    default is NULL.  (Create and set.)

GTTX_Border (BOOL)
    Set to TRUE to place a recessed border around the displayed string.
    The default is FALSE.  (Create only.)

GTTX_CopyText (BOOL)
    This flag instructs the text-display gadget to copy the supplied
    GTTX_Text string instead of using only a pointer to the string.  This
    only works for the value of GTTX_Text set at CreateGadget() time.  If
    GTTX_Text is changed, the new text will be referenced by pointer, not
    copied.  Do not use this tag without a non-NULL GTTX_Text.  (Create

Number-display gadgets have the following tags:

GTNM_Number (LONG)
    The number to be displayed.  The default is zero.  (Create or set.)

GTNM_Border (BOOL)
    Set to TRUE to place a recessed border around the displayed number.
    The default is FALSE.  (Create only.)

Since they are not selectable, text-display and numeric-display gadgets
never cause IntuiMessages to be sent to the application.

15 / / The Kinds of GadTools Gadgets / Generic Gadgets

If the application requires a specialized gadget which does not fit into
any of the defined GadTools kinds but would still like to use the GadTools
gadget creation and deletion functions, it may create a GadTools generic
gadget and use it any way it sees fit.  In fact, all of the kinds of
GadTools gadgets are created out of GadTools GENERIC_KIND gadgets.

The gadget that gets created will heed almost all the information
contained in the NewGadget structure supplied.

If ng_GadgetText is supplied, the Gadget's GadgetText will point to an
IntuiText structure with the provided string and font.  However, do not
specify any of the PLACETEXT ng_Flags, as they are currently ignored by
GENERIC_KIND gadgets.  PLACETEXT flags may be supported by generic
GadTools gadgets in the future.

It is up to the program to set the Flags, Activation, GadgetRender,
SelectRender, MutualExclude and SpecialInfo fields of the Gadget structure.

The application must also set the GadgetType field, but be certain to
preserve the bits set by CreateGadget(). For instance, to make a gadget
boolean, use:

    gad->GadgetType |= GTYP_BOOLGADGET;

and not

    gad->GadgetType = GTYP_BOOLGADGET;

Using direct assignment, (the = operator), clears all other flags in the
GadgetType field and the gadget may not be properly freed by FreeGadgets().

15 / GadTools / Functions for Setting Up GadTools Menus and Gadgets

This section gives all the details on the functions used to set up
GadTools menus and gadgets that were mentioned briefly earlier in this

 GetVisualInfo() and FreeVisualInfo()    CreateContext() 

15 / / / GetVisualInfo() and FreeVisualInfo()

In order to ensure their best appearance, GadTools gadgets and menus need
information about the screen on which they will appear.  Before creating
any GadTools gadgets or menus, the program must get this information using
the GetVisualInfo() call.

    APTR GetVisualInfoA( struct Screen *screen, struct TagItem *taglist );
    APTR GetVisualInfo( struct Screen *screen, Tag tag1, ... );

Set the screen argument to a pointer to the screen you are using.  The tag
arguments, tag1 or taglist, are reserved for future extensions.  Currently
none are recognized, so only TAG_END should be used.

The function returns an abstract handle called the VisualInfo.  For
GadTools gadgets, the ng_VisualInfo field of the NewGadget structure must
be set to this handle before the gadget can be added to the window.
GadTools menu layout and creation functions also require the VisualInfo
handle as an argument.

There are several ways to get the pointer to the screen on which the
window will be opened.  If the application has its own custom screen, this
pointer is known from the call to OpenScreen() or OpenScreenTags().  If
the application already has its window opened on the Workbench or some
other public screen, the screen pointer can be found in Window.WScreen.
Often the program will create its gadgets and menus before opening the
window.  In this case, use LockPubScreen() to get a pointer to the desired
public screen, which also provides a lock on the screen to prevent it from
closing.  See the chapters "Intuition Screens" and "Intuition Windows" for
more about public screens.

The VisualInfo data must be freed after all the gadgets and menus have
been freed but before releasing the screen.  Custom screens are released
by calling CloseScreen(), public screens are released by calling
CloseWindow() or UnlockPubScreen(), depending on the technique used.  Use
FreeVisualInfo() to free the visual info data.

    void FreeVisualInfo( APTR vi );

This function takes just one argument, the VisualInfo handle as returned
by GetVisualInfo().  The sequence of events for using the VisualInfo
handle could look like this:

    myscreen = LockPubScreen(NULL);
    if (!myscreen)
        cleanup("Failed to lock default public screen");
    vi = GetVisualInfo(myscreen);
    if (!vi)
        cleanup("Failed to GetVisualInfo");
    /* Create gadgets here */
    ng.ng_VisualInfo = vi;

    void cleanup(STRPTR errorstr)
    /* These functions may be safely called with a NULL parameter: */

    if (myscreen)
        UnlockPubScreen(NULL, myscreen);


15 / / Setting Up GadTools Menus and Gadgets / CreateContext()

Use of GadTools gadgets requires some per-window context information.
CreateContext() establishes a place for that information to go. This
function must be called before any GadTools gadgets are created.

    struct Gadget *CreateContext( struct Gadget **glistptr );

The glistptr argument is a double-pointer to a Gadget structure.  More
specifically, this is a pointer to a NULL-initialized pointer to a Gadget

The return value of CreateContext() is a pointer to this gadget, which
should be fed to the program's first call to CreateGadget().  This pointer
to the Gadget structure returned by CreateContext(), may then serve as a
handle to the list of gadgets as they are created.  The code fragment
listed in the next section shows how to use CreateContext() together with
CreateGadget() to make a linked list of GadTools gadgets.

15 / GadTools Gadgets / Creating Gadget Lists

In the discussion of CreateGadget() presented earlier, the examples showed
only how to make a single gadget.  For most applications that use
GadTools, however, a whole list of gadgets will be needed.  To do this,
the application could use code such as this:

    struct NewGadget *newgad1, *newgad2, *newgad3;
    struct Gadget *glist = NULL;
    struct Gadget *pgad;

    /* Initialize NewGadget structures */

    /* Note that CreateContext() requires a POINTER to a NULL-initialized
     * pointer to struct Gadget:
    pgad = CreateContext(&glist);

    pgad = CreateGadget(BUTTON_KIND, pgad, newgad1, TAG_END);
    pgad = CreateGadget(STRING_KIND, pgad, newgad2, TAG_END);
    pgad = CreateGadget(MX_KIND,     pgad, newgad3, TAG_END);

    if (!pgad)
        if ( mywin=OpenWindowTags(NULL,
                                  WA_Gadgets,   glist,
                                  /* Other tags... */
                                  TAG_END) )
            /* Complete the rendering of the gadgets */
            GT_RefreshWindow(win, NULL);
            /* and continue on... */


The pointer to the previous gadget, pgad in the code fragment above, is
used for three purposes.  First, when CreateGadget() is called multiple
times, each new gadget is automatically linked to the previous gadget's
NextGadget field, thus creating a gadget list.  Second, if one of the
gadget creations fails (usually due to low memory, but other causes are
possible), then for the next call to CreateGadget(), pgad will be NULL and
CreateGadget() will fail  immediately.  This means that the program can
perform several successive calls to CreateGadget() and only have to check
for failure at the end.

Finally, although this information is hidden in the implementation and not
important to the application, certain calls to CreateGadget() actually
cause several Intuition gadgets to be allocated and these are
automatically linked together without program interaction, but only if a
previous gadget pointer is supplied.  If several gadgets are created by a
single CreateGadget() call, they work together to provide the
functionality of a single GadTools gadget.  The application should always
act as though the gadget pointer returned by CreateGadget() points to a
single gadget instance.  See "Documented Side-Effects" for a warning.

There is one exception to the fact that a program only has to check for
failure after the last CreateGadget() call and that is when the
application depends on the successful creation of a gadget and caches or
immediately uses the gadget pointer returned by CreateGadget().

 For instance, if the program wants to create a string gadget and save a
pointer to the string buffer, it might do so as follows:

    gad = CreateGadget(STRING_KIND, gad, &ng,
                            GTST_String, "Hello World",
    if (gad)
        stringbuffer = ((struct StringInfo *)(gad->SpecialInfo))->Buffer;

    /* Creation can continue here: */
    gad = CreateGadget(..._KIND, gad, &ng2,

A major benefit of having a reusable NewGadget structure is that often
many fields do not change and some fields change incrementally.  For
example, the application can set just the NewGadget's ng_VisualInfo and
ng_TextAttr only once and never have to modify them again even if the
structure is reused to create many gadgets.  A set of similar gadgets may
share size and some positional information so that code such as the
following might be used:

    /* Assume that the NewGadget structure 'ng' is fully
     * initialized here for a button labelled "OK"
    gad = CreateGadget(BUTTON_KIND, gad, &ng,

    /* Modify only those fields that need to change: */
    ng.ng_LeftEdge += 80;
    ng.ng_GadgetText = "Cancel";
    gad = CreateGadget(BUTTON_KIND, gad, &ng,

    All gadgets created by GadTools currently have the GADTOOL_TYPE bit
    set in their GadgetType field.  It is not correct to check for,
    set, clear or otherwise rely on this since it is subject to change.

15 / GadTools Gadgets / Gadget Refresh Functions

Normally, GadTools gadgets are created and then attached to a window when
the window is opened, either through the WA_Gadget tag or the
NewWindow.FirstGadget field.  Alternately, they may be added to a window
after it is open by using the functions AddGList() and RefreshGList().

Regardless of which way gadgets are attached to a window, the program must
then call the GT_RefreshWindow() function to complete the rendering of
GadTools gadgets.  This function takes two arguments.

    void GT_RefreshWindow( struct Window *win, struct Requester *req );

This win argument is a pointer to the window that contains the GadTools
gadgets.  The req argument is currently unused and should be set to NULL.
This function should only be called immediately after adding GadTools
gadgets to a window.  Subsequent changes to GadTools gadget imagery made
through calls to GT_SetGadgetAttrs() will be automatically performed by
GadTools when the changes are made.  (There is no need to call
GT_RefreshWindow() in that case.)

As mentioned earlier, applications must always ask for notification of
window refresh events for any window that uses GadTools gadgets.  When the
application receives an IDCMP_REFRESHWINDOW message for a window,
Intuition has already refreshed its gadgets.  Normally, a program would
then call Intuition's BeginRefresh(), perform its own custom rendering
operations, and finally call EndRefresh().  But for a window that uses
GadTools gadgets, the application must call GT_BeginRefresh() and
GT_EndRefresh() in place of BeginRefresh() and EndRefresh().  This allows
the the GadTools gadgets to be fully refreshed.

    void GT_BeginRefresh( struct Window *win );
    void GT_EndRefresh ( struct Window *win, long complete );

For both functions, the win argument is a pointer to the window to be
refreshed.  For GT_EndRefresh(), set the complete argument to TRUE if
refreshing is complete, set it to FALSE otherwise.  See the discussion of
BeginRefresh() and EndRefresh() in the "Intuition Windows" chapter for
more about window refreshing.

When using GadTools gadgets, the program may not set the window's
WFLG_NOCAREREFRESH flag.  Even if there is no custom rendering to be
performed, GadTools gadgets requires this minimum code to handle

        /* custom rendering, if any, goes here */
        GT_EndRefresh(win, TRUE);

15 / GadTools Gadgets / Other GadTools Functions

This section discusses some additional support functions in the GadTools
library that serve special needs.

 GT_FilterIMsg() and GT_PostFilterIMsg()    DrawBevelBox() 

15 / / Other Functions / GT_FilterIMsg() and GT_PostFilterIMsg()

For most GadTools programs, GT_GetIMsg() and GT_ReplyIMsg() work perfectly
well.  In rare cases an application may find they pose a bit of a problem.
A typical case is when all messages are supposed to go through a
centralized ReplyMsg() that cannot be converted to a GT_ReplyIMsg().
Since calls to GT_GetIMsg() and GT_ReplyIMsg() must be paired, there would
be a problem.

For such cases, the GT_FilterIMsg() and GT_PostFilterIMsg() functions are
available.  These functions allow GetMsg() and ReplyMsg() to be used in a
way that is compatible with GadTools.

    These functions are for specialized use only and will not be used by
    the majority of applications.  See GT_GetIMsg() and
    GT_ReplyIMsg() for standard message handling.

    struct IntuiMessage *GT_FilterIMsg( struct IntuiMessage *imsg );
    struct IntuiMessage *GT_PostFilterIMsg( struct IntuiMessage *imsg );

The GT_FilterIMsg() function should be called right after GetMsg().  It
takes a pointer to the original IntuiMessage and, if the message applies
to a GadTools gadget, returns either a modified IntuiMessage or a NULL.  A
NULL return signifies that the message was consumed by a GadTools gadget
(and not needed by the application).

The GT_PostFilterIMsg() function should be called before replying to any
message modified by GT_FilterIMsg().  It takes a pointer to the modified
version of an IntuiMessage obtained with GT_FilterIMsg() and returns a
pointer to the original IntuiMessage.

The typical calling sequence for a program that uses these functions, is
to call GetMsg() to get the IntuiMessage.  Then, if the message applies to
a window which contains GadTools gadgets, call GT_FilterIMsg().  Any
message returned by GT_FilterIMsg() should be used like a message returned
from GT_GetIMsg().

When done with the message, the application must call GT_PostFilterIMsg()
to perform any clean up necessitated by the previous call to
GT_FilterIMsg().  In all cases, the application must then reply the
original IntuiMessage using ReplyMsg().  This is true even for consumed
messages as these are not replied by GadTools.  For example, the
application could use code such as this:

    /* port is a message port receiving different messages */
    /* gtwindow is the window that contains GadTools gadgets */

    imsg = GetMsg(port);

    /* Is this the window with GadTools gadgets? */
    if (imsg->IDCMPWindow == gtwindow)
        /* Filter the message and see if action is needed */
        if (gtimsg = GT_FilterIMsg(imsg))
            switch (gtimsg->Class)
                /* Act depending on the message */
            /* Clean up the filtered message.  The return value is not */
            /* needed since we already have a pointer to the original  */
            /* message.                                                */
    /* other stuff can go here */

You should not make any assumptions about the contents of the unfiltered
IntuiMessage (imsg in the above example).  Only two things are guaranteed:
the unfiltered IntuiMessage must be replied to and the unfiltered
IntuiMessage (if it produces anything when passed through GT_FilterIMsg())
will produce a meaningful GadTools IntuiMessage like those described in
the section on the different kinds of gadgets.  The relationship between
the unfiltered and filtered messages are expected to change in the future.
See the section on documented side-effects for more information.

15 / / Other GadTools Functions / DrawBevelBox()

A key visual signature shared by most GadTools gadgets is the raised or
recessed bevelled box imagery.  Since the program may wish to create its
own boxes to match, GadTools provides the DrawBevelBox() and
DrawBevelBoxA() functions.

    void DrawBevelBoxA( struct RastPort *rport, long left, long top,
                        long width, long height, struct TagItem *taglist );
    void DrawBevelBox ( struct RastPort *rport, long left, long top,
                        long width, long height, Tag tag1, ... );

The rport argument is a pointer to the RastPort into which the box is to
be rendered.  The left, top, width and height arguments specify the
dimensions of the desired box.

The tag arguments, tag1 or taglist, may be set as follows:

GT_VisualInfo (APTR)
    The VisualInfo handle as returned by a prior call to GetVisualInfo().
    This value is required.

GTBB_Recessed (BOOL)
    A bevelled box may either appear to be raised to signify an area of
    the window that is selectable or recessed to signify an area of the
    window in which clicking will have no effect.  Set this boolean tag
    to TRUE to get a recessed box.  Omit this tag entirely to get a
    raised box.

DrawBevelBox() is a rendering operation, not a gadget. This means that the
program must refresh any bevelled boxes rendered through this function if
the window gets damaged.

15 / GadTools Gadgets / Gadget Keyboard Equivalents

Often, users find it convenient to control gadgets using the keyboard.
Starting with V37, it is possible to denote the keyboard equivalent for a
GadTools gadget.  The keyboard equivalent will be an underscored character
in the gadget label, for easy identification.  At the present time,
however, the application is still responsible for implementing the
reaction to each keypress.

 Denoting a Gadget's Keyboard Equivalent 
 Implementing a Gadget's Keyboard Equivalent Behavior 

15 / / Keyboard Equivalents / Denoting a Gadget's Keyboard Equivalent

In order to denote the key equivalent, the application may add a
marker-symbol to the gadget label.  This is done by placing the
marker-symbol immediately before the character to be underscored.  This
symbol can be any character that is not used in the label.  The underscore
character, `_' is the recommended marker-symbol.  So, for example, to mark
the letter "F" as the keyboard equivalent for a button labelled "Select
Font...", create the gadget text:

    ng.ng_GadgetText = "Select _Font...";

To inform GadTools of the underscore in the label, pass the GA_Underscore
tag to CreateGadget() or CreateGadgetA().  The data-value associated with
this tag is a character, not a string, which is the marker-symbol used in
the gadget label:

    GA_Underscore, '_',/* Note '_', not "_" !!! */

GadTools will create a gadget label which consists of the text supplied
with the marker-symbol removed and the character following the
marker-symbol underscored.

The gadget's label would look something like:

    Select Font...

15 / / / Implementing a Gadget's Keyboard Equivalent Behavior

Currently, GadTools does not process keyboard equivalents for gadgets.  It
is up to the application writer to implement the correct behavior,
normally by calling GT_SetGadgetAttrs() on the appropriate gadget.  For
some kinds of gadget, the behavior should be the same regardless of
whether the keyboard equivalent was pressed with or without the shift key.
For other gadgets, shifted and unshifted keystrokes will have different,
usually opposite, effects.

Here is the correct behavior for keyboard equivalents for each kind of
GadTools gadget:

Button Gadgets
    The keyboard equivalent should invoke the same function that clicking
    on the gadget does.  There is currently no way to highlight the
    button visuals programmatically when accessing the button through a
    keyboard equivalent.

Text-Entry and Number-Entry Gadgets
    The keyboard equivalent should activate the gadget so the user may
    type into it.  Use Intuition's ActivateGadget() call.

Checkbox Gadgets
    The keyboard equivalent should toggle the state of the checkbox.  Use
    GT_SetGadgetAttrs() and the GTCB_Checked tag.

Mutually-Exclusive Gadgets
    The unshifted keystroke should activate the next choice, wrapping
    around from the last to the first.  The shifted keystroke should
    activate the previous choice, wrapping around from the first to the
    last.  Use GT_SetGadgetAttrs() and the GTMX_Active tag.

Cycle Gadgets
    The unshifted keystroke should activate the next choice, wrapping
    around from the last to the first.  The shifted keystroke should
    activate the previous choice, wrapping around from the first to the
    last.  Use GT_SetGadgetAttrs() and the GTCY_Active tag.

Slider Gadgets
    The unshifted keystroke should increase the slider's level by one,
    stopping at the maximum, while the shifted keystroke should decrease
    the level by one, stopping at the minimum.  Use GT_SetGadgetAttrs()
    and the GTSL_Level tag.

Scroller Gadgets
    The unshifted keystroke should increase the scroller's top by one,
    stopping at the maximum, while the shifted keystroke should decrease
    the scroller's top by one, stopping at the minimum.  Use
    GT_SetGadgetAttrs() and the GTSC_Top tag.

Listview Gadgets
    The unshifted keystroke should cause the next entry in the list to
    become the selected one, stopping at the last entry, while the
    shifted keystroke should cause the previous entry in the list to
    become the selected one, stopping at the first entry.  Use
    GT_SetGadgetAttrs() and the GTLV_Top and GTLV_Selected tags.

Palette Gadgets
    The unshifted keystroke should select the next color, wrapping around
    from the last to the first.  The shifted keystroke should activate
    the previous color, wrapping around from the first to the last.  Use
    GT_SetGadgetAttrs() and the GTPA_Color tag.

Text-Display and Number-Display Gadgets
    These kinds of GadTools gadget have no keyboard equivalents since
    they are not selectable.

Generic Gadgets
    Define appropriate keyboard functions based on the kinds of keyboard
    behavior defined for other GadTools kinds.

15 / GadTools Gadgets / Restrictions on GadTools Gadgets

There is a strict set of functions and operations that are permitted on
GadTools gadgets.  Even if a technique is discovered that works for a
particular case, be warned that it cannot be guaranteed and should not be
used.  If the trick concocted only works most of the time, it may
introduce subtle problems in the future.

Never selectively or forcibly refresh gadgets.  The only gadget refresh
that should ever be performed is the initial GT_RefreshWindow() after a
window is opened with GadTools gadgets attached.  It is also possible to
add gadgets after the window is opened by calling AddGlist() and
RefreshGlist() followed by GT_RefreshWindow().  These refresh functions
should not be called at any other time.

GadTools gadgets may not overlap with each other, with other gadgets or
with other imagery.  Doing this to modify the gadget's appearance is not

GadTools gadgets may not be selectively added or removed from a window.
This has to do with the number of Intuition gadgets that each call to
CreateGadget() produces and with refresh constraints.

Never use OnGadget() or OffGadget() or directly modify the GFLG_DISABLED
Flags bit.  The only approved way to disable or enable a gadget is to use
GT_SetGadgetAttrs() and the GA_Disabled tag.  Those kinds of GadTools
gadgets that do not support GA_Disabled may not be disabled (for now).

The application should never write into any of the fields of the Gadget
structure or any of the structures that hang off it, with the exception
noted earlier for GENERIC_KIND gadgets.  Avoid making assumptions about
the contents of these fields unless they are explicitly programmer fields
(GadgetID and UserData, for example) or if they are guaranteed meaningful
(LeftEdge, TopEdge, Width, Height, Flags).  On occasion, the program is
specifically invited to read a field, for example the StringInfo->Buffer

GadTools gadgets may not be made relative sized or relative positioned.
This means that the gadget flags GFLG_RELWIDTH, GFLG_RELHEIGHT,
GFLG_RELBOTTOM and GFLG_RELRIGHT may not be specified.  The activation
type of the gadget may not be modified (for example changing
GACT_IMMEDIATE to GACT_RELVERIFY).  The imagery or the highlighting method
may not be changed.

These restrictions are not imposed without reason; subtle or blatant
problems may arise now or in future versions of GadTools for programs that
violate these guidelines.

15 / GadTools Gadgets / Documented Side-Effects

There are certain aspects of the behavior of GadTools gadgets that should
not be depended on. This will help current applications remain compatible
with future releases of the GadTools library.

When using GT_FilterIMsg() and GT_PostFilterIMsg(), never make assumptions
about the message before or after filtering.  I.e., do not interpret the
unfiltered message, assume that it will or will not result in certain
kinds of filtered message or assume it will result in a consumed message
(i.e., when GT_FilterIMsg() returns NULL).

IDCMP_INTUITICKS messages are consumed when a scroller's arrows are
repeating.  That is, IDCMP_INTUITICKS will not be received while the user
is pressing a scroller arrows.  Do not depend or rely on this side effect,
though, it will not necessarily remain so in the future.

A single call to CreateGadget() may create one or more actual gadgets.
These gadgets, along with the corresponding code in GadTools, define the
behavior of the particular kind of GadTools gadget requested.  Only the
behavior of these gadgets is documented, the number or type of actual
gadgets is subject to change.  Always refer to the gadget pointer received
from CreateGadget() when calling GT_SetGadgetAttrs().  Never refer to
other gadgets created by GadTools, nor create code which depends on their
number or form.

For text-display gadgets, the GTTX_CopyText tag does not cause the text to
be copied when the text is later changed with GTTX_Text.

The PLACETEXT ng_Flags are currently ignored by GENERIC_KIND gadgets.
However, this may not always be so.

All GadTools gadgets set GADTOOL_TYPE in the gadget's GadgetType field.
Do not use this flag to identify GadTools gadgets, as this flag is not
guaranteed to be set in the future.

The palette gadget subdivides its total area into the individual color
squares. Do not assume that the subdivision algorithm won't change.

15 GadTools Library / Function Reference

The following are brief descriptions of the Intuition functions discussed
in this chapter.  See the "Amiga ROM Kernel Reference Manual: Includes and
Autodocs" for details on each function call.  All of these functions
require Release 2 or a later version of the operating system.

               Table 15-2: GadTools Library Functions
 |                                                                      |
 |          Function                  Description                       |
 |       CreateGadgetA()  Allocate GadTools gadget, tag array form.     |
 |        CreateGadget()  Allocate GadTools gadget, varargs form.       |
 |         FreeGadgets()  Free all GadTools gadgets.                    |
 |  GT_SetGadgetAttrsA()  Update gadget, tag array form.                |
 |   GT_SetGadgetAttrs()  Update gadget, varargs form.                  |
 |       CreateContext()  Create a base for adding GadTools gadgets.    |
 |        CreateMenusA()  Allocate GadTools menu structures, tag array  |
 |                        form.                                         |
 |         CreateMenus()  Allocate GadTools menu structures, varargs    |
 |                        form.                                         |
 |           FreeMenus()  Free menus allocated with CreateMenus().      |
 |    LayoutMenuItemsA()  Format GadTools menu items, tag array form.   |
 |     LayoutMenuItems()  Format GadTools menu items, varargs form.     |
 |        LayoutMenusA()  Format GadTools menus, tag array form.        |
 |         LayoutMenus()  Format GadTools menus, varargs form.          |
 |          GT_GetIMsg()  GadTools gadget compatible version of         |
 |                        GetMsg().                                     |
 |        GT_ReplyIMsg()  GadTools gadget compatible version of         |
 |                        ReplyMsg().                                   |
 |       GT_FilterIMsg()  Process GadTools gadgets with                 |
 |                        GetMsg()/ReplyMsg().                          |
 |   GT_PostFilterIMsg()  Process GadTools gadgets with                 |
 |                        GetMsg()/ReplyMsg().                          |
 |    GT_RefreshWindow()  Display GadTools gadget imagery after         |
 |                        creation.                                     |
 |     GT_BeginRefresh()  GadTools gadget compatible version of         |
 |                        BeginRefresh().                               |
 |       GT_EndRefresh()  GadTools gadget compatible version of         |
 |                        EndRefresh().                                 |
 |       DrawBevelBoxA()  Draw a 3D box, tag array form.                |
 |        DrawBevelBox()  Draw a 3D box, varargs form.                  |
 |      GetVisualInfoA()  Get drawing information for GadTools, tag     |
 |                        array form.                                   |
 |       GetVisualInfo()  Get drawing information for GadTools, varargs |
 |                        form.                                         |
 |      FreeVisualInfo()  Free drawing information for GadTools.        |

Converted on 22 Apr 2000 with RexxDoesAmigaGuide2HTML 2.1 by Michael Ranner.