Tk_SetOptions(3)

NAME
Tk_CreateOptionTable, Tk_DeleteOptionTable, Tk_InitOptions, Tk_SetOptions, Tk_FreeSavedOptions, Tk_RestoreSavedOptions, Tk_GetOptionValue, Tk_GetOptionInfo, Tk_FreeConfigOptions, Tk_Offset - process configuration options

SYNOPSIS
#include <tk.h>

Tk_OptionTable
Tk_CreateOptionTable(interp, templatePtr)

Tk_DeleteOptionTable(optionTable)

int
Tk_InitOptions(interp, recordPtr, optionTable, tkwin)

int
Tk_SetOptions(interp, recordPtr, optionTable, objc, objv, tkwin, savePtr, maskPtr)

Tk_FreeSavedOptions(savedPtr)

Tk_RestoreSavedOptions(savedPtr)

Tcl_Obj *
Tk_GetOptionValue(interp, recordPtr, optionTable, namePtr, tkwin)

Tcl_Obj *
Tk_GetOptionInfo(interp, recordPtr, optionTable, namePtr, tkwin)

Tk_FreeConfigOptions(recordPtr, optionTable, tkwin)

int
Tk_Offset(type, field)

ARGUMENTS
A Tcl interpreter. Most procedures use this only for returning error messages; if it is NULL then no error messages are returned. For Tk_CreateOptionTable the value cannot be NULL; it gives the interpreter in which the option table will be used. Points to an array of static information that describes the configuration options that are supported. Used to build a Tk_OptionTable. The information pointed to by this argument must exist for the lifetime of the Tk_OptionTable. Token for an option table. Must have been returned by a previous call to Tk_CreateOptionTable. Points to structure in which values of configuration options are stored; fields of this record are modified by procedures such as Tk_SetOptions and read by procedures such as Tk_GetOptionValue. For options such as TK_OPTION_COLOR, this argument indicates the window in which the option will be used. If optionTable uses no window-dependent options, then a NULL value may be supplied for this argument. Number of values in objv. Command-line arguments for setting configuring options. If not NULL, the structure pointed to by this argument is filled in with the old values of any options that were modified and old values are restored automatically if an error occurs in Tk_SetOptions. If not NULL, the word pointed to by maskPtr is filled in with the bit-wise OR of the typeMask fields for the options that were modified. Points to a structure previously filled in by Tk_SetOptions with old values of modified options. The value of this object is the name of a particular option. If NULL is passed to Tk_GetOptionInfo then information is returned for all options. Must not be NULL when Tk_GetOptionValue is called. The name of the type of a record. The name of a field in records of type type.

DESCRIPTION

These procedures handle most of the details of parsing configuration options such as those for Tk widgets. Given a description of what options are supported, these procedures handle all the details of parsing options and storing their values into a C structure associated with the widget or object. The procedures were designed primarily for widgets in Tk, but they can also be used for other kinds of objects that have configuration options. In the rest of this manual page will be used to refer to the object whose options are being managed; in practice the object may not actually be a widget. The term is used to refer to the C-level structure in which information about a particular widget or object is stored.

Note: the easiest way to learn how to use these procedures is to look at a working example. In Tk, the simplest example is the code that implements the button family of widgets, which is in tkButton.c. Other examples are in tkSquare.c and tkMenu.c.

In order to use these procedures, the code that implements the widget must contain a static array of Tk_OptionSpec structures. This is a template that describes the various options supported by that class of widget; there is a separate template for each kind of widget. The template contains information such as the name of each option, its type, its default value, and where the value of the option is stored in the widget record. See TEMPLATES below for more detail.

In order to process configuration options efficiently, the static template must be augmented with additional information that is available only at runtime. The procedure Tk_CreateOptionTable creates this dynamic information from the template and returns a Tk_OptionTable token that describes both the static and dynamic information. All of the other procedures, such as Tk_SetOptions, take a Tk_OptionTable token as argument. Typically, Tk_CreateOptionTable is called the first time that a widget of a particular class is created and the resulting Tk_OptionTable is used in the future for all widgets of that class. A Tk_OptionTable may be used only in a single interpreter, given by the interp argument to Tk_CreateOptionTable. When an option table is no longer needed Tk_DeleteOptionTable should be called to free all of its resources. All of the option tables for a Tcl interpreter are freed automatically if the interpreter is deleted.

Tk_InitOptions is invoked when a new widget is created to set the default values for all of the widget's configuration options. Tk_InitOptions is passed a token for an option table (optionTable) and a pointer to a widget record (recordPtr), which is the C structure that holds information about this widget. Tk_InitOptions uses the information in the option table to choose an appropriate default for each option, then it stores the default value directly into the widget record, overwriting any information that was already present in the widget record. Tk_InitOptions normally returns TCL_OK. If an error occurred while setting the default values (e.g., because a default value was erroneous) then TCL_ERROR is returned and an error message is left in interp's result if interp is not NULL.

Tk_SetOptions is invoked to modify configuration options based on information specified in a Tcl command. The command might be one that creates a new widget, or a command that modifies options on an existing widget. The objc and objv arguments describe the values of the arguments from the Tcl command. Objv must contain an even number of objects: the first object of each pair gives the name of an option and the second object gives the new value for that option. Tk_SetOptions looks up each name in optionTable, checks that the new value of the option conforms to the type in optionTable, and stores the value of the option into the widget record given by recordPtr. Tk_SetOptions normally returns TCL_OK. If an error occurred (such as an unknown option name or an illegal option value) then TCL_ERROR is returned and an error message is left in interp's result if interp is not NULL.

Tk_SetOptions has two additional features. First, if the maskPtr argument is not NULL then it points to an integer value that is filled in with information about the options that were modified. For each option in the template passed to Tk_CreateOptionTable there is a typeMask field. The bits of this field are defined by the code that implements the widget; for example, each bit might correspond to a particular configuration option. Alternatively, bits might be used functionally. For example, one bit might be used for redisplay: all options that affect the widget's display, such that changing the option requires the widget to be redisplayed, might have that bit set. Another bit might indicate that the geometry of the widget must be recomputed, and so on. Tk_SetOptions OR's together the typeMask fields from all the options that were modified and returns this value at *maskPtr; the caller can then use this information to optimize itself so that, for example, it does not redisplay the widget if the modified options do not affect the widget's appearance.

The second additional feature of Tk_SetOptions has to do with error recovery. If an error occurs while processing configuration options, this feature makes it possible to restore all the configuration options to their previous values. Errors can occur either while processing options in Tk_SetOptions or later in the caller. In many cases the caller does additional processing after Tk_SetOptions returns; for example, it might use an option value to set a trace on a variable and may detect an error if the variable is an array instead of a scalar. Error recovery is enabled by passing in a non-NULL value for the savePtr argument to Tk_SetOptions; this should be a pointer to an uninitialized Tk_SavedOptions structure on the caller's stack. Tk_SetOptions overwrites the structure pointed to by savePtr with information about the old values of any options modified by the procedure. If Tk_SetOptions returns successfully, the caller uses the structure in one of two ways. If the caller completes its processing of the new options without any errors, then it must pass the structure to Tk_FreeSavedOptions so that the old values can be freed. If the caller detects an error in its processing of the new options, then it should pass the structure to Tk_RestoreSavedOptions, which will copy the old values back into the widget record and free the new values. If Tk_SetOptions detects an error then it automatically restores any options that had already been modified and leaves *savePtr in an empty state: the caller need not call either Tk_FreeSavedOptions or Tk_RestoreSavedOptions. If the savePtr argument to Tk_SetOptions is NULL then Tk_SetOptions frees each old option value immediately when it sets a new value for the option. In this case, if an error occurs in the third option, the old values for the first two options cannot be restored.

Tk_GetOptionValue returns the current value of a configuration option for a particular widget. The namePtr argument contains the name of an option; Tk_GetOptionValue uses optionTable to lookup the option and extract its value from the widget record pointed to by recordPtr, then it returns an object containing that value. If an error occurs (e.g., because namePtr contains an unknown option name) then NULL is returned and an error message is left in interp's result unless interp is NULL.

Tk_GetOptionInfo returns information about configuration options in a form suitable for configure widget commands. If the namePtr argument is not NULL, it points to an object that gives the name of a configuration option; Tk_GetOptionInfo returns an object containing a list with five elements, which are the name of the option, the name and class used for the option in the option database, the default value for the option, and the current value for the option. If the namePtr argument is NULL, then Tk_GetOptionInfo returns information about all options in the form of a list of lists; each sublist describes one option. Synonym options are handled differently depending on whether namePtr is NULL: if namePtr is NULL then the sublist for each synonym option has only two elements, which are the name of the option and the name of the other option that it refers to; if namePtr is non-NULL and names a synonym option then the object returned is the five-element list for the other option that the synonym refers to. If an error occurs (e.g., because namePtr contains an unknown option name) then NULL is returned and an error message is left in interp's result unless interp is NULL.

Tk_FreeConfigOptions must be invoked when a widget is deleted. It frees all of the resources associated with any of the configuration options defined in recordPtr by optionTable.

The Tk_Offset macro is provided as a safe way of generating the objOffset and internalOffset values for entries in Tk_OptionSpec 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.

TEMPLATES

The array of Tk_OptionSpec structures passed to Tk_CreateOptionTable via its templatePtr argument describes the configuration options supported by a particular class of widgets. Each structure specifies one configuration option and has the following fields:
    typedef struct {
        Tk_OptionType type;
        const char *optionName;
        const char *dbName;
        const char *dbClass;
        const char *defValue;
        int objOffset;
        int internalOffset;
        int flags;
        ClientData clientData;
        int typeMask;
    } Tk_OptionSpec;
The type field indicates what kind of configuration option this is (e.g. TK_OPTION_COLOR for a color value, or TK_OPTION_INT for an integer value). Type determines how the value of the option is parsed (more on this below). The optionName field is a string such as -font or -bg; it is the name used for the option in Tcl commands and passed to procedures via the objc or namePtr arguments. The dbName and dbClass fields are used by Tk_InitOptions to look up a default value for this option in the option database; if dbName is NULL then the option database is not used by Tk_InitOptions for this option. The defValue field specifies a default value for this configuration option if no value is specified in the option database. The objOffset and internalOffset fields indicate where to store the value of this option in widget records (more on this below); values for the objOffset and internalOffset fields should always be generated with the Tk_Offset macro. The flags field contains additional information to control the processing of this configuration option (see below for details). ClientData provides additional type-specific data needed by certain types. For instance, for TK_OPTION_COLOR types, clientData is a string giving the default value to use on monochrome displays. See the descriptions of the different types below for details. The last field, typeMask, is used by Tk_SetOptions to return information about which options were modified; see the description of Tk_SetOptions above for details.

When Tk_InitOptions and Tk_SetOptions store the value of an option into the widget record, they can do it in either of two ways. If the objOffset field of the Tk_OptionSpec is greater than or equal to zero, then the value of the option is stored as a (Tcl_Obj *) at the location in the widget record given by objOffset. If the internalOffset field of the Tk_OptionSpec is greater than or equal to zero, then the value of the option is stored in a type-specific internal form at the location in the widget record given by internalOffset. For example, if the option's type is TK_OPTION_INT then the internal form is an integer. If the objOffset or internalOffset field is negative then the value is not stored in that form. At least one of the offsets must be greater than or equal to zero.

The flags field consists of one or more bits ORed together. At present only a single flag is supported: TK_OPTION_NULL_OK. If this bit is set for an option then an empty string will be accepted as the value for the option and the resulting internal form will be a NULL pointer, a zero value, or None, depending on the type of the option. If the flag is not set then empty strings will result in errors. TK_OPTION_NULL_OK 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. Not all option types support the TK_OPTION_NULL_OK flag; for those that do, there is an explicit indication of that fact in the descriptions below.

The type field of each Tk_OptionSpec structure determines how to parse the value of that configuration option. The legal value for type, and the corresponding actions, are described below. If the type requires a tkwin value to be passed into procedures like Tk_SetOptions, or if it uses the clientData field of the Tk_OptionSpec, then it is indicated explicitly; if not mentioned, the type requires neither tkwin nor clientData.

TK_OPTION_ANCHOR
    The value must be a standard anchor position such as ne or center. The internal form is a Tk_Anchor value like the ones returned by Tk_GetAnchorFromObj.

TK_OPTION_BITMAP
    The value must be a standard Tk bitmap name. The internal form is a Pixmap token like the ones returned by Tk_AllocBitmapFromObj. This option type requires tkwin to be supplied to procedures such as Tk_SetOptions, and it supports the TK_OPTION_NULL_OK flag.

TK_OPTION_BOOLEAN
    The value must be a standard boolean value such as true or no. The internal form is an integer with value 0 or 1.

TK_OPTION_BORDER
    The value must be a standard color name such as red or #ff8080. The internal form is a Tk_3DBorder token like the ones returned by Tk_Alloc3DBorderFromObj. This option type requires tkwin to be supplied to procedures such as Tk_SetOptions, and it supports the TK_OPTION_NULL_OK flag.

TK_OPTION_COLOR
    The value must be a standard color name such as red or #ff8080. The internal form is an (XColor *) token like the ones returned by Tk_AllocColorFromObj. This option type requires tkwin to be supplied to procedures such as Tk_SetOptions, and it supports the TK_OPTION_NULL_OK flag.

TK_OPTION_CURSOR
    The value must be a standard cursor name such as cross or @foo. The internal form is a Tk_Cursor token like the ones returned by Tk_AllocCursorFromObj. This option type requires tkwin to be supplied to procedures such as Tk_SetOptions, and when the option is set the cursor for the window is changed by calling XDefineCursor. This option type also supports the TK_OPTION_NULL_OK flag.

TK_OPTION_CUSTOM
    This option allows applications to define new option types. The clientData field of the entry points to a structure defining the new option type. See the section CUSTOM OPTION TYPES below for details.

TK_OPTION_DOUBLE
    The string value must be a floating-point number in the format accepted by strtol. The internal form is a C double value. This option type supports the TK_OPTION_NULL_OK flag; if a NULL value is set, the internal representation is set to zero.

TK_OPTION_END
    Marks the end of the template. There must be a Tk_OptionSpec structure with type TK_OPTION_END at the end of each template. If the clientData field of this structure is not NULL, then it points to an additional array of Tk_OptionSpec's, which is itself terminated by another TK_OPTION_END entry. Templates may be chained arbitrarily deeply. This feature allows common options to be shared by several widget classes.

TK_OPTION_FONT
    The value must be a standard font name such as Times 16. The internal form is a Tk_Font handle like the ones returned by Tk_AllocFontFromObj. This option type requires tkwin to be supplied to procedures such as Tk_SetOptions, and it supports the TK_OPTION_NULL_OK flag.

TK_OPTION_INT
    The string value must be an integer in the format accepted by strtol (e.g. 0 and 0x prefixes may be used to specify octal or hexadecimal numbers, respectively). The internal form is a C int value.

TK_OPTION_JUSTIFY
    The value must be a standard justification value such as left. The internal form is a Tk_Justify like the values returned by Tk_GetJustifyFromObj.

TK_OPTION_PIXELS
    The value must specify a screen distance such as 2i or 6.4. The internal form is an integer value giving a distance in pixels, like the values returned by Tk_GetPixelsFromObj. Note: if the objOffset field is not used then information about the original value of this option will be lost. See OBJOFFSET VS. INTERNALOFFSET below for details. This option type supports the TK_OPTION_NULL_OK flag; if a NULL value is set, the internal representation is set to zero.

TK_OPTION_RELIEF
    The value must be standard relief such as raised. The internal form is an integer relief value such as TK_RELIEF_RAISED. This option type supports the TK_OPTION_NULL_OK flag; if the empty string is specified as the value for the option, the integer relief value is set to TK_RELIEF_NULL.

TK_OPTION_STRING
    The value may be any string. The internal form is a (char *) pointer that points to a dynamically allocated copy of the value. This option type supports the TK_OPTION_NULL_OK flag.

TK_OPTION_STRING_TABLE
    For this type, clientData is a pointer to an array of strings suitable for passing to Tcl_GetIndexFromObj. The value must be one of the strings in the table, or a unique abbreviation of one of the strings. The internal form is an integer giving the index into the table of the matching string, like the return value from Tcl_GetStringFromObj.

TK_OPTION_SYNONYM
    This type is used to provide alternative names for an option (for example, -bg is often used as a synonym for -background). The clientData field is a (char *) pointer that gives the name of another option in the same table. Whenever the synonym option is used, the information from the other option will be used instead.

TK_OPTION_WINDOW
    The value must be a window path name. The internal form is a Tk_Window token for the window. This option type requires tkwin to be supplied to procedures such as Tk_SetOptions (in order to identify the application), and it supports the TK_OPTION_NULL_OK flag.

STORAGE MANAGEMENT ISSUES

If a field of a widget record has its offset stored in the objOffset or internalOffset field of a Tk_OptionSpec structure then the procedures described here will handle all of the storage allocation and resource management issues associated with the field. When the value of an option is changed, Tk_SetOptions (or Tk_FreeSavedOptions) will automatically free any resources associated with the old value, such as Tk_Fonts for TK_OPTION_FONT options or dynamically allocated memory for TK_OPTION_STRING options. For an option stored as an object using the objOffset field of a Tk_OptionSpec, the widget record shares the object pointed to by the objv value from the call to Tk_SetOptions. The reference count for this object is incremented when a pointer to it is stored in the widget record and decremented when the option is modified. When the widget is deleted Tk_FreeConfigOptions should be invoked; it will free the resources associated with all options and decrement reference counts for any objects.

However, the widget code is responsible for storing NULL or None in all pointer and token fields before invoking Tk_InitOptions. This is needed to allow proper cleanup in the rare case where an error occurs in Tk_InitOptions.

OBJOFFSET VS. INTERNALOFFSET

In most cases it is simplest to use the internalOffset field of a Tk_OptionSpec structure and not the objOffset field. This makes the internal form of the value immediately available to the widget code so the value does not have to be extracted from an object each time it is used. However, there are two cases where the objOffset field is useful. The first case is for TK_OPTION_PIXELS options. In this case, the internal form is an integer pixel value that is valid only for a particular screen. If the value of the option is retrieved, it will be returned as a simple number. For example, after the command .b configure -borderwidth 2m, the command .b configure -borderwidth might return 7, which is the integer pixel value corresponding to 2m. Unfortunately, this loses the original screen-independent value. Thus for TK_OPTION_PIXELS options it is better to use the objOffset field. In this case the original value of the option is retained in the object and can be returned when the option is retrieved. In most cases it is convenient to use the internalOffset field as well, so that the integer value is immediately available for use in the widget code (alternatively, Tk_GetPixelsFromObj can be used to extract the integer value from the object whenever it is needed). Note: the problem of losing information on retrievals exists only for TK_OPTION_PIXELS options.

The second reason to use the objOffset field is in order to implement new types of options not supported by these procedures. To implement a new type of option, you can use TK_OPTION_STRING as the type in the Tk_OptionSpec structure and set the objOffset field but not the internalOffset field. Then, after calling Tk_SetOptions, convert the object to internal form yourself.

CUSTOM OPTION TYPES

Applications can extend the built-in configuration types with additional configuration types by writing procedures to parse, print, free, and restore saved copies of the type and creating a structure pointing to those procedures:
    typedef struct Tk_ObjCustomOption {
        char *name;
        Tk_CustomOptionSetProc *setProc;
        Tk_CustomOptionGetProc *getProc;
        Tk_CustomOptionRestoreProc *restoreProc;
        Tk_CustomOptionFreeProc *freeProc;
        ClientData clientData;
    } Tk_ObjCustomOption;

    typedef int Tk_CustomOptionSetProc(
        ClientData clientData,
        Tcl_Interp *interp,
        Tk_Window tkwin,
        Tcl_Obj **valuePtr,
        char *recordPtr,
        int internalOffset,
        char *saveInternalPtr,
        int flags);

    typedef Tcl_Obj *Tk_CustomOptionGetProc(
        ClientData clientData,
        Tk_Window tkwin,
        char *recordPtr,
        int internalOffset);

    typedef void Tk_CustomOptionRestoreProc(
        ClientData clientData,
        Tk_Window tkwin,
        char *internalPtr,
        char *saveInternalPtr);

    typedef void Tk_CustomOptionFreeProc(
        ClientData clientData,
        Tk_Window tkwin,
        char *internalPtr);

The Tk_ObjCustomOption structure contains six fields: a name for the custom option type; pointers to the four 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. RestoreProc and freeProc may be NULL, indicating that no function should be called for those operations.

The setProc procedure is invoked by Tk_SetOptions to convert a Tcl_Obj into an internal representation and store the resulting value in the widget record. The arguments are:

    clientData
        A copy of the clientData field in the Tk_ObjCustomOption structure.

    interp
        A pointer to a Tcl interpreter, used for error reporting.

    Tkwin
        A copy of the tkwin argument to Tk_SetOptions

    valuePtr
        A pointer to a reference to a Tcl_Obj describing the new value for the option; it could have been specified explicitly in the call to Tk_SetOptions or it could come from the option database or a default. If the objOffset for the option is non-negative (the option value is stored as a (Tcl_Obj *) in the widget record), the Tcl_Obj pointer referenced by valuePtr is the pointer that will be stored at the objOffset for the option. SetProc may modify the value if necessary; for example, setProc may change the value to NULL to support the TK_OPTION_NULL_OK flag.

    recordPtr
        A pointer to the start of the widget record to modify.

    internalOffset
        Offset in bytes from the start of the widget record to the location where the internal representation of the option value is to be placed.

    saveInternalPtr
        A pointer to storage allocated in a Tk_SavedOptions structure for the internal representation of the original option value. Before setting the option to its new value, setProc should set the value referenced by saveInternalPtr to the original value of the option in order to support Tk_RestoreSavedOptions.

    flags
        A copy of the flags field in the Tk_OptionSpec structure for the option

SetProc returns a standard Tcl result: TCL_OK to indicate successful processing, or TCL_ERROR to indicate a failure of any kind. An error message may be left in the Tcl interpreter given by interp in the case of an error.

The getProc procedure is invoked by Tk_GetOptionValue and Tk_GetOptionInfo to retrieve a Tcl_Obj representation of the internal representation of an option. The clientData argument is a copy of the clientData field in the Tk_ObjCustomOption structure. Tkwin is a copy of the tkwin argument to Tk_GetOptionValue or Tk_GetOptionInfo. RecordPtr is a pointer to the beginning of the widget record to query. InternalOffset is the offset in bytes from the beginning of the widget record to the location where the internal representation of the option value is stored. GetProc must return a pointer to a Tcl_Obj representing the value of the option.

The restoreProc procedure is invoked by Tk_RestoreSavedOptions to restore a previously saved internal representation of a custom option value. The clientData argument is a copy of the clientData field in the Tk_ObjCustomOption structure. Tkwin is a copy of the tkwin argument to Tk_GetOptionValue or Tk_GetOptionInfo. InternalPtr is a pointer to the location where internal representation of the option value is stored. SaveInternalPtr is a pointer to the saved value. RestoreProc must copy the value from saveInternalPtr to internalPtr to restore the value. RestoreProc need not free any memory associated with either internalPtr or saveInternalPtr; freeProc will be invoked to free that memory if necessary. RestoreProc has no return value.

The freeProc procedure is invoked by Tk_SetOptions and Tk_FreeSavedOptions to free any storage allocated for the internal representation of a custom option. The clientData argument is a copy of the clientData field in the Tk_ObjCustomOption structure. Tkwin is a copy of the tkwin argument to Tk_GetOptionValue or Tk_GetOptionInfo. InternalPtr is a pointer to the location where the internal representation of the option value is stored. The freeProc must free any storage associated with the option. FreeProc has no return value.

KEYWORDS
anchor, bitmap, boolean, border, color, configuration option, cursor, double, font, integer, justify, pixels, relief, screen distance, synonym