Specifying Widget Attributes
Several of the fields in the Clock structure are attributes that can be set when the widget is created or reconfigured with the configure operation. The Tk_ConfigureWidget procedure is designed to help you manage the default values, their resource names, and their class names. It works by associating a widget option with an offset into the widget data structure. When you use a command line argument to change an option, Tk_ConfigureWidget reaches into your widget structure and changes the value for you. Several types are supported, such as colors and fonts, and Tk_ConfigureWidget handles all the memory allocation used to store the values. Example 46-9 shows the Tk_ConfigSpec type used to represent information about each attribute:
Example 46-9 The Tk_ConfigSpec typedef.
typedef struct Tk_ConfigSpec {
int type;
char *name;
char *dbName;
char *dbClass;
char *defValue;
int offset;
int specflags;
Tk_CustomOption *customPtr;
} Tk_ConfigSpec;
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The initial field is a type, such as TK_CONFIG_BORDER. Colors and borders will be explained shortly. The next field is the command-line flag for the attribute, (e.g., -background). Then comes the resource name and the class name. The default value is next, (e.g., light blue). The offset of a structure member is next, and the Tk_Offset macro is used to compute this offset. The specflags field is a bitmask of flags. The two used in this example are TK_CONFIG_COLOR_ONLY and TK_CONFIG_MONO_ONLY, which restrict the application of the configuration setting to color and monochrome displays, respectively. You can define additional flags and pass them into Tk_ConfigureWidget if you have a family of widgets that share most, but not all, of their attributes. The tkButton.c file in the Tk sources has an example of this. The customPtr is used if you have a TK_CONFIG_CUSTOM type, which is explained in detail in the manual page for Tk_ConfigureWidget. Example 46-10 shows the Tk_ConfigSpec specification of widget attributes for the clock widget.
Example 46-10 Configuration specs for the clock widget.
static Tk_ConfigSpec configSpecs[] = {
{TK_CONFIG_BORDER, "-background", "background",
"Background", "light blue",
Tk_Offset(Clock, background), TK_CONFIG_COLOR_ONLY},
{TK_CONFIG_BORDER, "-background", "background",
"Background", "white", Tk_Offset(Clock, background),
TK_CONFIG_MONO_ONLY},
{TK_CONFIG_SYNONYM, "-bg", "background", (char *) NULL,
(char *) NULL, 0, 0},
{TK_CONFIG_SYNONYM, "-bd", "borderWidth", (char *) NULL,
(char *) NULL, 0, 0},
{TK_CONFIG_PIXELS, "-borderwidth", "borderWidth",
"BorderWidth","2", Tk_Offset(Clock, borderWidth), 0},
{TK_CONFIG_RELIEF, "-relief", "relief", "Relief",
"ridge", Tk_Offset(Clock, relief), 0},
{TK_CONFIG_COLOR, "-foreground", "foreground",
"Foreground", "black", Tk_Offset(Clock, foreground),
0},
{TK_CONFIG_SYNONYM, "-fg", "foreground", (char *) NULL,
(char *) NULL, 0, 0},
{TK_CONFIG_COLOR, "-highlightcolor", "highlightColor",
"HighlightColor", "red", Tk_Offset(Clock, highlight),
TK_CONFIG_COLOR_ONLY},
{TK_CONFIG_COLOR, "-highlightcolor", "highlightColor",
"HighlightColor", "black",
Tk_Offset(Clock, highlight),TK_CONFIG_MONO_ONLY},
{TK_CONFIG_COLOR, "-highlightbackground",
"highlightBackground", "HighlightBackground",
"light blue", Tk_Offset(Clock, highlightBg),
TK_CONFIG_COLOR_ONLY},
{TK_CONFIG_COLOR, "-highlightbackground",
"highlightBackground", "HighlightBackground",
"black", Tk_Offset(Clock, highlightBg),
TK_CONFIG_MONO_ONLY},
{TK_CONFIG_PIXELS, "-highlightthickness",
"highlightThickness","HighlightThickness",
"2", Tk_Offset(Clock, highlightWidth), 0},
{TK_CONFIG_PIXELS, "-padx", "padX", "Pad",
"2", Tk_Offset(Clock, padX), 0},
{TK_CONFIG_PIXELS, "-pady", "padY", "Pad",
"2", Tk_Offset(Clock, padY), 0},
{TK_CONFIG_STRING, "-format", "format", "Format",
"%H:%M:%S", Tk_Offset(Clock, format), 0},
{TK_CONFIG_FONT, "-font", "font", "Font",
"Courier 18",
Tk_Offset(Clock, tkfont), 0},
{TK_CONFIG_END, (char *) NULL, (char *) NULL,
(char *) NULL, (char *) NULL, 0, 0}
};
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There is an alternative to the Tk_ConfigureWidget interface that understands Tcl_Obj values in the widget data structure. It uses a a similar type, Tk_OptionSpec, and Tk_ConfigureWidget is replaced by the Tk_SetOptions, Tk_GetOptionValue, and Tk_GetOptionInfo procedures. Example 46-11 shows the Tk_OptionSpec type.
Example 46-11 The Tk_OptionSpec typedef.
The Tk_OptionSpec has two offsets, one for normal values and one for Tcl_Obj values. You can use the second offset to set Tcl_Obj values directly from the command line configuration. The TK_CONFIG_PIXELS type uses both offsets. The pixel value is stored in an integer, and a Tcl_Obj is used to remember the exact string (e.g., 0.2cm) used to specify the screen distance. Most of the functionality of the specflags field of Tk_ConfigSpec (e.g., TK_CONFIG_MONO_ONLY) has been changed. The flags field accepts only TK_CONFIG_NULL_OK, and the rest of the features use the clientData field instead. For example, the color types uses clientData for their default on monochrome displays. The typeMask supports a general notion of grouping option values into sets. For example, the clock widget marks attributes that affect geometry and color into different sets. This lets the widget optimize its configuration procedure. Example 46-12 shows the Tk_OptionSpec specification of the clock widget attributes.
Example 46-12 The Tk_OptionSpec structure for the clock widget.
Table 46-1 lists the correspondence between the configuration type of the option and the type of the associated field in the widget data structure. The same types are supported by the Tk_ConfigSpec and Tk_OptionSpec types, with a few exceptions. The TK_CONFIG_ACTIVE_CURSOR configuration type corresponds to the TK_OPTION_CURSOR; both of these set the widgets cursor. The TK_CONFIG_MM and TK_CONFIG_CURSOR types are simply not supported by Tk_OptionSpec because they were not very useful. The TK_OPTION_STRING_TABLE replaces TK_CONFIG_CAP_STYLE and TK_CONFIG_JOIN_STYLE with a more general type that works with Tcl_GetIndexFromObj. In this case, the clientData is an array of strings that are passed to Tcl_GetIndexFromObj. The index value corresponds to the integer value returned from procedures like Tk_GetCapStyle.
| TK_CONFIG_ACTIVE_CURSOR TK_OPTION_CURSOR | Cursor |
| TK_CONFIG_ANCHOR TK_OPTION_ANCHOR | Tk_Anchor |
| TK_CONFIG_BITMAP TK_OPTION_BITMAP | Pixmap |
| TK_CONFIG_BOOLEAN TK_OPTION_BOOLEAN | int (0 or 1) |
| TK_CONFIG_BORDER TK_OPTION_BORDER | Tk_3DBorder * |
| TK_CONFIG_CAP_STYLE | int (see Tk_GetCapStyle) |
| TK_CONFIG_COLOR TK_OPTION_COLOR | XColor * clientData is monochrome default. |
| TK_CONFIG_CURSOR | Cursor |
| TK_CONFIG_CUSTOM | |
| TK_CONFIG_DOUBLE TK_OPTION_DOUBLE | double |
| TK_CONFIG_END TK_OPTION_END | (signals end of options) |
| TK_CONFIG_FONT TK_OPTION_FONT | Tk_Font |
| TK_CONFIG_INT TK_OPTION_INT | int |
| TK_CONFIG_JOIN_STYLE | int (see Tk_GetJoinStyle) |
| TK_CONFIG_JUSTIFY TK_OPTION_JUSTIFY | Tk_Justify |
| TK_CONFIG_MM | double |
| TK_CONFIG_PIXELS TK_OPTION_PIXELS | int objOffset used for original value. |
| TK_CONFIG_RELIEF TK_OPTION_RELIEF | int (see Tk_GetRelief) |
| TK_CONFIG_STRING TK_OPTION_STRING | char * |
| TK_OPTION_STRING_TABLE | The clientData is an array of strings used with Tcl_GetIndexFromObj |
| TK_CONFIG_SYNONYM TK_OPTION_SYNONYM | (alias for other option) clientData is the name of another option. |
| TK_CONFIG_UID | Tk_Uid |
| TK_CONFIG_WINDOW TK_OPTION_WINDOW | Tk_Window |