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
Interpreter to use for returning error messages. Window used to represent widget (needed to set up X resources). Pointer to table specifying legal configuration options for this widget. Number of arguments in argv. Command-line options for configuring widget. Points to widget record structure. Fields in this structure get modified by Tk_ConfigureWidget to hold configuration information. 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. The name of the type of a widget record. The name of a field in records of type type. 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 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 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.

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 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 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 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.

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.

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 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 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; 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 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