Tk_ConfigureWidget(3) Tk (4.1) Tk_ConfigureWidget(3)
_________________________________________________________________
NAME
Tk_ConfigureWidget, Tk_Offset, Tk_ConfigureInfo,
Tk_ConfigureValue, Tk_FreeOptions - process configuration
options for widgets
SYNOPSIS
#include <tk.h>
int
Tk_ConfigureWidget(interp, tkwin, specs, argc, argv, widgRec, flags)
int
Tk_Offset(type, field)
int
Tk_ConfigureInfo(interp, tkwin, specs, widgRec, argvName, flags)
int
Tk_FreeOptions(specs, widgRec, display, flags)
ARGUMENTS
Tcl_Interp *interp (in) Interpreter to use for
returning error
messages.
Tk_Window tkwin (in) Window used to
represent widget
(needed to set up X
resources).
Tk_ConfigSpec *specs (in) Pointer to table
specifying legal
configuration options
for this widget.
int argc (in) Number of arguments in
argv.
char **argv (in) Command-line options
for configuring widget.
char *widgRec (in/out) Points to widget record
structure. Fields in
this structure get
modified by
Tk_ConfigureWidget to
hold configuration
information.
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int flags (in) If non-zero, then it
specifies an OR-ed
combination of flags
that control the
processing of
configuration
information.
TK_CONFIG_ARGV_ONLY
causes the option
database and defaults
to be ignored, and flag
bits TK_CONFIG_USER_BIT
and higher are used to
selectively disable
entries in specs.
type name type (in) The name of the type of
a widget record.
field name field (in) The name of a field in
records of type type.
char *argvName (in) The name used on Tcl
command lines to refer
to a particular option
(e.g. when creating a
widget or invoking the
configure widget
command). If non-NULL,
then information is
returned only for this
option. If NULL, then
information is returned
for all available
options.
Display *display (in) Display containing
widget whose record is
being freed; needed in
order to free up
resources.
_________________________________________________________________
DESCRIPTION
Tk_ConfigureWidget is called to configure various aspects of
a widget, such as colors, fonts, border width, etc. It is
intended as a convenience procedure to reduce the amount of
code that must be written in individual widget managers to
handle configuration information. It is typically invoked
when widgets are created, and again when the configure
command is invoked for a widget. Although intended
primarily for widgets, Tk_ConfigureWidget can be used in
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other situations where argc-argv information is to be used
to fill in a record structure, such as configuring graphical
elements for a canvas widget or entries of a menu.
Tk_ConfigureWidget processes a table specifying the
configuration options that are supported (specs) and a
collection of command-line arguments (argc and argv) to fill
in fields of a record (widgRec). It uses the option
database and defaults specified in specs to fill in fields
of widgRec that are not specified in argv.
Tk_ConfigureWidget normally returns the value TCL_OK; in
this case it does not modify interp. If an error occurs
then TCL_ERROR is returned and Tk_ConfigureWidget will leave
an error message in interp->result in the standard Tcl
fashion. In the event of an error return, some of the
fields of widgRec could already have been set, if
configuration information for them was successfully
processed before the error occurred. The other fields will
be set to reasonable initial values so that Tk_FreeOptions
can be called for cleanup.
The specs array specifies the kinds of configuration options
expected by the widget. Each of its entries specifies one
configuration option and has the following structure:
typedef struct {
int type;
char *argvName;
char *dbName;
char *dbClass;
char *defValue;
int offset;
int specFlags;
Tk_CustomOption *customPtr;
} Tk_ConfigSpec;
The type field indicates what type of configuration option
this is (e.g. TK_CONFIG_COLOR for a color value, or
TK_CONFIG_INT for an integer value). The type field
indicates how to use the value of the option (more on this
below). The argvName field is a string such as ``-font'' or
``-bg'', which is compared with the values in argv (if
argvName is NULL it means this is a grouped entry; see
GROUPED ENTRIES below). The dbName and dbClass fields are
used to look up a value for this option in the option
database. The defValue field specifies a default value for
this configuration option if no value is specified in either
argv or the option database. Offset indicates where in
widgRec to store information about this option, and
specFlags contains additional information to control the
processing of this configuration option (see FLAGS below).
The last field, customPtr, is only used if type is
TK_CONFIG_CUSTOM; see CUSTOM OPTION TYPES below.
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Tk_ConfigureWidget first processes argv to see which (if
any) configuration options are specified there. Argv must
contain an even number of fields; the first of each pair of
fields must match the argvName of some entry in specs
(unique abbreviations are acceptable), and the second field
of the pair contains the value for that configuration
option. If there are entries in spec for which there were
no matching entries in argv, Tk_ConfigureWidget uses the
dbName and dbClass fields of the specs entry to probe the
option database; if a value is found, then it is used as
the value for the option. Finally, if no entry is found in
the option database, the defValue field of the specs entry
is used as the value for the configuration option. If the
defValue is NULL, or if the TK_CONFIG_DONT_SET_DEFAULT bit
is set in flags, then there is no default value and this
specs entry will be ignored if no value is specified in argv
or the option database.
Once a string value has been determined for a configuration
option, Tk_ConfigureWidget translates the string value into
a more useful form, such as a color if type is
TK_CONFIG_COLOR or an integer if type is TK_CONFIG_INT.
This value is then stored in the record pointed to by
widgRec. This record is assumed to contain information
relevant to the manager of the widget; its exact type is
unknown to Tk_ConfigureWidget. The offset field of each
specs entry indicates where in widgRec to store the
information about this configuration option. You should use
the Tk_Offset macro to generate offset values (see below for
a description of Tk_Offset). The location indicated by
widgRec and offset will be referred to as the ``target'' in
the descriptions below.
The type field of each entry in specs determines what to do
with the string value of that configuration option. The
legal values for type, and the corresponding actions, are:
TK_CONFIG_ACTIVE_CURSOR
The value must be an ASCII string identifying a cursor
in a form suitable for passing to Tk_GetCursor. The
value is converted to a Tk_Cursor by calling
Tk_GetCursor and the result is stored in the target.
In addition, the resulting cursor is made the active
cursor for tkwin by calling XDefineCursor. If
TK_CONFIG_NULL_OK is specified in specFlags then the
value may be an empty string, in which case the target
and tkwin's active cursor will be set to None. If the
previous value of the target wasn't None, then it is
freed by passing it to Tk_FreeCursor.
TK_CONFIG_ANCHOR
The value must be an ASCII string identifying an anchor
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point in one of the ways accepted by Tk_GetAnchor. The
string is converted to a Tk_Anchor by calling
Tk_GetAnchor and the result is stored in the target.
TK_CONFIG_BITMAP
The value must be an ASCII string identifying a bitmap
in a form suitable for passing to Tk_GetBitmap. The
value is converted to a Pixmap by calling Tk_GetBitmap
and the result is stored in the target. If
TK_CONFIG_NULL_OK is specified in specFlags then the
value may be an empty string, in which case the target
is set to None. If the previous value of the target
wasn't None, then it is freed by passing it to
Tk_FreeBitmap.
TK_CONFIG_BOOLEAN
The value must be an ASCII string specifying a boolean
value. Any of the values ``true'', ``yes'', ``on'', or
``1'', or an abbreviation of one of these values, means
true; any of the values ``false'', ``no'', ``off'', or
``0'', or an abbreviation of one of these values, means
false. The target is expected to be an integer; for
true values it will be set to 1 and for false values it
will be set to 0.
TK_CONFIG_BORDER
The value must be an ASCII string identifying a border
color in a form suitable for passing to Tk_Get3DBorder.
The value is converted to a (Tk_3DBorder *) by calling
Tk_Get3DBorder and the result is stored in the target.
If TK_CONFIG_NULL_OK is specified in specFlags then the
value may be an empty string, in which case the target
will be set to NULL. If the previous value of the
target wasn't NULL, then it is freed by passing it to
Tk_Free3DBorder.
TK_CONFIG_CAP_STYLE
The value must be an ASCII string identifying a cap
style in one of the ways accepted by Tk_GetCapStyle.
The string is converted to an integer value
corresponding to the cap style by calling
Tk_GetCapStyle and the result is stored in the target.
TK_CONFIG_COLOR
The value must be an ASCII string identifying a color
in a form suitable for passing to Tk_GetColor. The
value is converted to an (XColor *) by calling
Tk_GetColor and the result is stored in the target. If
TK_CONFIG_NULL_OK is specified in specFlags then the
value may be an empty string, in which case the target
will be set to None. If the previous value of the
target wasn't NULL, then it is freed by passing it to
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Tk_FreeColor.
TK_CONFIG_CURSOR
This option is identical to TK_CONFIG_ACTIVE_CURSOR
except that the new cursor is not made the active one
for tkwin.
TK_CONFIG_CUSTOM
This option allows applications to define new option
types. The customPtr field of the entry points to a
structure defining the new option type. See the
section CUSTOM OPTION TYPES below for details.
TK_CONFIG_DOUBLE
The value must be an ASCII floating-point number in the
format accepted by strtol. The string is converted to
a double value, and the value is stored in the target.
TK_CONFIG_END
Marks the end of the table. The last entry in specs
must have this type; all of its other fields are
ignored and it will never match any arguments.
TK_CONFIG_FONT
The value must be an ASCII string identifying a font in
a form suitable for passing to Tk_GetFontStruct. The
value is converted to an (XFontStruct *) by calling
Tk_GetFontStruct and the result is stored in the
target. If TK_CONFIG_NULL_OK is specified in specFlags
then the value may be an empty string, in which case
the target will be set to NULL. If the previous value
of the target wasn't NULL, then it is freed by passing
it to Tk_FreeFontStruct.
TK_CONFIG_INT
The value must be an ASCII integer string in the format
accepted by strtol (e.g. ``0'' and ``0x'' prefixes may
be used to specify octal or hexadecimal numbers,
respectively). The string is converted to an integer
value and the integer is stored in the target.
TK_CONFIG_JOIN_STYLE
The value must be an ASCII string identifying a join
style in one of the ways accepted by Tk_GetJoinStyle.
The string is converted to an integer value
corresponding to the join style by calling
Tk_GetJoinStyle and the result is stored in the target.
TK_CONFIG_JUSTIFY
The value must be an ASCII string identifying a
justification method in one of the ways accepted by
Tk_GetJustify. The string is converted to a Tk_Justify
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by calling Tk_GetJustify and the result is stored in
the target.
TK_CONFIG_MM
The value must specify a screen distance in one of the
forms acceptable to Tk_GetScreenMM. The string is
converted to double-precision floating-point distance
in millimeters and the value is stored in the target.
TK_CONFIG_PIXELS
The value must specify screen units in one of the forms
acceptable to Tk_GetPixels. The string is converted to
an integer distance in pixels and the value is stored
in the target.
TK_CONFIG_RELIEF
The value must be an ASCII string identifying a relief
in a form suitable for passing to Tk_GetRelief. The
value is converted to an integer relief value by
calling Tk_GetRelief and the result is stored in the
target.
TK_CONFIG_STRING
A copy of the value is made by allocating memory space
with malloc and copying the value into the
dynamically-allocated space. A pointer to the new
string is stored in the target. If TK_CONFIG_NULL_OK
is specified in specFlags then the value may be an
empty string, in which case the target will be set to
NULL. If the previous value of the target wasn't NULL,
then it is freed by passing it to free.
TK_CONFIG_SYNONYM
This type value identifies special entries in specs
that are synonyms for other entries. If an argv value
matches the argvName of a TK_CONFIG_SYNONYM entry, the
entry isn't used directly. Instead, Tk_ConfigureWidget
searches specs for another entry whose argvName is the
same as the dbName field in the TK_CONFIG_SYNONYM
entry; this new entry is used just as if its argvName
had matched the argv value. The synonym mechanism
allows multiple argv values to be used for a single
configuration option, such as ``-background'' and
``-bg''.
TK_CONFIG_UID
The value is translated to a Tk_Uid (by passing it to
Tk_GetUid). The resulting value is stored in the
target. If TK_CONFIG_NULL_OK is specified in specFlags
and the value is an empty string then the target will
be set to NULL.
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TK_CONFIG_WINDOW
The value must be a window path name. It is translated
to a Tk_Window token and the token is stored in the
target.
GROUPED ENTRIES
In some cases it is useful to generate multiple resources
from a single configuration value. For example, a color
name might be used both to generate the background color for
a widget (using TK_CONFIG_COLOR) and to generate a 3-D
border to draw around the widget (using TK_CONFIG_BORDER).
In cases like this it is possible to specify that several
consecutive entries in specs are to be treated as a group.
The first entry is used to determine a value (using its
argvName, dbName, dbClass, and defValue fields). The value
will be processed several times (one for each entry in the
group), generating multiple different resources and
modifying multiple targets within widgRec. Each of the
entries after the first must have a NULL value in its
argvName field; this indicates that the entry is to be
grouped with the entry that precedes it. Only the type and
offset fields are used from these follow-on entries.
FLAGS
The flags argument passed to Tk_ConfigureWidget is used in
conjunction with the specFlags fields in the entries of
specs to provide additional control over the processing of
configuration options. These values are used in three
different ways as described below.
First, if the flags argument to Tk_ConfigureWidget has the
TK_CONFIG_ARGV_ONLY bit set (i.e., flags |
TK_CONFIG_ARGV_ONLY != 0), then the option database and
defValue fields are not used. In this case, if an entry in
specs doesn't match a field in argv then nothing happens:
the corresponding target isn't modified. This feature is
useful when the goal is to modify certain configuration
options while leaving others in their current state, such as
when a configure widget command is being processed.
Second, the specFlags field of an entry in specs may be used
to control the processing of that entry. Each specFlags
field may consists of an OR-ed combination of the following
values:
TK_CONFIG_COLOR_ONLY
If this bit is set then the entry will only be
considered if the display for tkwin has more than one
bit plane. If the display is monochromatic then this
specs entry will be ignored.
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TK_CONFIG_MONO_ONLY
If this bit is set then the entry will only be
considered if the display for tkwin has exactly one bit
plane. If the display is not monochromatic then this
specs entry will be ignored.
TK_CONFIG_NULL_OK
This bit is only relevant for some types of entries
(see the descriptions of the various entry types
above). If this bit is set, it indicates that an empty
string value for the field is acceptable and if it
occurs then the target should be set to NULL or None,
depending on the type of the target. This flag is
typically used to allow a feature to be turned off
entirely, e.g. set a cursor value to None so that a
window simply inherits its parent's cursor. If this
bit isn't set then empty strings are processed as
strings, which generally results in an error.
TK_CONFIG_DONT_SET_DEFAULT
If this bit is one, it means that the defValue field of
the entry should only be used for returning the default
value in Tk_ConfigureInfo. In calls to
Tk_ConfigureWidget no default will be supplied for
entries with this flag set; it is assumed that the
caller has already supplied a default value in the
target location. This flag provides a performance
optimization where it is expensive to process the
default string: the client can compute the default
once, save the value, and provide it before calling
Tk_ConfigureWidget.
TK_CONFIG_OPTION_SPECIFIED
This bit is set and cleared by Tk_ConfigureWidget.
Whenever Tk_ConfigureWidget returns, this bit will be
set in all the entries where a value was specified in
argv. It will be zero in all other entries. This bit
provides a way for clients to determine which values
actually changed in a call to Tk_ConfigureWidget.
The TK_CONFIG_MONO_ONLY and TK_CONFIG_COLOR_ONLY flags are
typically used to specify different default values for
monochrome and color displays. This is done by creating two
entries in specs that are identical except for their
defValue and specFlags fields. One entry should have the
value TK_CONFIG_MONO_ONLY in its specFlags and the default
value for monochrome displays in its defValue; the other
entry entry should have the value TK_CONFIG_COLOR_ONLY in
its specFlags and the appropriate defValue for color
displays.
Third, it is possible to use flags and specFlags together to
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selectively disable some entries. This feature is not
needed very often. It is useful in cases where several
similar kinds of widgets are implemented in one place. It
allows a single specs table to be created with all the
configuration options for all the widget types. When
processing a particular widget type, only entries relevant
to that type will be used. This effect is achieved by
setting the high-order bits (those in positions equal to or
greater than TK_CONFIG_USER_BIT) in specFlags values or in
flags. In order for a particular entry in specs to be used,
its high-order bits must match exactly the high-order bits
of the flags value passed to Tk_ConfigureWidget. If a specs
table is being used for N different widget types, then N of
the high-order bits will be used. Each specs entry will
have one of more of those bits set in its specFlags field to
indicate the widget types for which this entry is valid.
When calling Tk_ConfigureWidget, flags will have a single
one of these bits set to select the entries for the desired
widget type. For a working example of this feature, see the
code in tkButton.c.
TK_OFFSET
The Tk_Offset macro is provided as a safe way of generating
the offset values for entries in Tk_ConfigSpec structures.
It takes two arguments: the name of a type of record, and
the name of a field in that record. It returns the byte
offset of the named field in records of the given type.
TK_CONFIGUREINFO
The Tk_ConfigureInfo procedure may be used to obtain
information about one or all of the options for a given
widget. Given a token for a window (tkwin), a table
describing the configuration options for a class of widgets
(specs), a pointer to a widget record containing the current
information for a widget (widgRec), and a NULL argvName
argument, Tk_ConfigureInfo generates a string describing all
of the configuration options for the window. The string is
placed in interp->result. Under normal circumstances it
returns TCL_OK; if an error occurs then it returns
TCL_ERROR and interp->result contains an error message.
If argvName is NULL, then the value left in interp->result
by Tk_ConfigureInfo consists of a list of one or more
entries, each of which describes one configuration option
(i.e. one entry in specs). Each entry in the list will
contain either two or five values. If the corresponding
entry in specs has type TK_CONFIG_SYNONYM, then the list
will contain two values: the argvName for the entry and the
dbName (synonym name). Otherwise the list will contain five
values: argvName, dbName, dbClass, defValue, and current
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value. The current value is computed from the appropriate
field of widgRec by calling procedures like Tk_NameOfColor.
If the argvName argument to Tk_ConfigureInfo is non-NULL,
then it indicates a single option, and information is
returned only for that option. The string placed in
interp->result will be a list containing two or five values
as described above; this will be identical to the
corresponding sublist that would have been returned if
argvName had been NULL.
The flags argument to Tk_ConfigureInfo is used to restrict
the specs entries to consider, just as for
Tk_ConfigureWidget.
TK_CONFIGUREVALUE
Tk_ConfigureValue takes arguments similar to
Tk_ConfigureInfo; instead of returning a list of values, it
just returns the current value of the option given by
argvName (argvName must not be NULL). The value is returned
in interp->result and TCL_OK is normally returned as the
procedure's result. If an error occurs in Tk_ConfigureValue
(e.g., argvName is not a valid option name), TCL_ERROR is
returned and an error message is left in interp->result.
This procedure is typically called to implement cget widget
commands.
TK_FREEOPTIONS
The Tk_FreeOptions procedure may be invoked during widget
cleanup to release all of the resources associated with
configuration options. It scans through specs and for each
entry corresponding to a resource that must be explicitly
freed (e.g. those with type TK_CONFIG_COLOR), it frees the
resource in the widget record. If the field in the widget
record doesn't refer to a resource (e.g. it contains a null
pointer) then no resource is freed for that entry. After
freeing a resource, Tk_FreeOptions sets the corresponding
field of the widget record to null.
CUSTOM OPTION TYPES
Applications can extend the built-in configuration types
with additional configuration types by writing procedures to
parse and print options of the a type and creating a
structure pointing to those procedures:
typedef struct Tk_CustomOption {
Tk_OptionParseProc *parseProc;
Tk_OptionPrintProc *printProc;
ClientData clientData;
} Tk_CustomOption;
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typedef int Tk_OptionParseProc(
ClientData clientData,
Tcl_Interp *interp,
Tk_Window tkwin,
char *value,
char *widgRec,
int offset);
typedef char *Tk_OptionPrintProc(
ClientData clientData,
Tk_Window tkwin,
char *widgRec,
int offset,
Tcl_FreeProc **freeProcPtr);
The Tk_CustomOption structure contains three fields, which
are pointers to the two procedures and a clientData value to
be passed to those procedures when they are invoked. The
clientData value typically points to a structure containing
information that is needed by the procedures when they are
parsing and printing options.
The parseProc procedure is invoked by Tk_ConfigureWidget to
parse a string and store the resulting value in the widget
record. The clientData argument is a copy of the clientData
field in the Tk_CustomOption structure. The interp argument
points to a Tcl interpreter used for error reporting. Tkwin
is a copy of the tkwin argument to Tk_ConfigureWidget. The
value argument is a string describing the value for the
option; it could have been specified explicitly in the call
to Tk_ConfigureWidget or it could come from the option
database or a default. Value will never be a null pointer
but it may point to an empty string. RecordPtr is the same
as the widgRec argument to Tk_ConfigureWidget; it points to
the start of the widget record to modify. The last
argument, offset, gives the offset in bytes from the start
of the widget record to the location where the option value
is to be placed. The procedure should translate the string
to whatever form is appropriate for the option and store the
value in the widget record. It should normally return
TCL_OK, but if an error occurs in translating the string to
a value then it should return TCL_ERROR and store an error
message in interp->result.
The printProc procedure is called by Tk_ConfigureInfo to
produce a string value describing an existing option. Its
clientData, tkwin, widgRec, and offset arguments all have
the same meaning as for Tk_OptionParseProc procedures. The
printProc procedure should examine the option whose value is
stored at offset in widgRec, produce a string describing
that option, and return a pointer to the string. If the
string is stored in dynamically-allocated memory, then the
procedure must set *freeProcPtr to the address of a
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procedure to call to free the string's memory;
Tk_ConfigureInfo will call this procedure when it is
finished with the string. If the result string is stored in
static memory then printProc need not do anything with the
freeProcPtr argument.
Once parseProc and printProc have been defined and a
Tk_CustomOption structure has been created for them, options
of this new type may be manipulated with Tk_ConfigSpec
entries whose type fields are TK_CONFIG_CUSTOM and whose
customPtr fields point to the Tk_CustomOption structure.
EXAMPLES
Although the explanation of Tk_ConfigureWidget is fairly
complicated, its actual use is pretty straightforward. The
easiest way to get started is to copy the code from an
existing widget. The library implementation of frames
(tkFrame.c) has a simple configuration table, and the
library implementation of buttons (tkButton.c) has a much
more complex table that uses many of the fancy specFlags
mechanisms.
KEYWORDS
anchor, bitmap, boolean, border, cap style, color,
configuration options, cursor, custom, double, font,
integer, join style, justify, millimeters, pixels, relief,
synonym, uid
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