# Public Header File

The public header file contains declarations that will be required by any application module that needs to refer to the widget; whether to create an instance of the class, to perform an operation, or to call a public routine implemented by the widget class.

The contents of the Template public header file, `<X11/Xaw/Template.h>`, are:

    ..

    /* Copyright (c) X Consortium 1987, 1988 */

    #ifndef _Template_h
    #define _Template_h

    /****************************************************************
     *
     * Template widget
     *
     ****************************************************************/

    /* Resources:

     Name	Class		RepType	Default Value
     ----		-----		-------	-------------
     background	Background		Pixel	XtDefaultBackground
     border	BorderColor		Pixel	XtDefaultForeground
     borderWidth	BorderWidth		Dimension	1
     destroyCallback	Callback		Pointer	NULL
     height	Height		Dimension	0
     mappedWhenManaged	MappedWhenManaged	Boolean	True
     sensitive	Sensitive		Boolean	True
     width	Width		Dimension	0
     x		Position		Position	0
     y		Position		Position	0

    */

    /* define any special resource names here that are not in <X11/StringDefs.h> */

    #define XtNtemplateResource "templateResource"

    #define XtCTemplateResource "TemplateResource"

    /* declare specific TemplateWidget class and instance datatypes */

    typedef struct _TemplateClassRec*	TemplateWidgetClass;
    typedef struct _TemplateRec*	TemplateWidget;

    /* declare the class constant */

    extern WidgetClass templateWidgetClass;

    #endif /* _Template_h */

You will notice that most of this file is documentation. The crucial parts are the last 8 lines where macros for any private resource names and classes are defined and where the widget class datatypes and class record pointer are declared.

For the "WindowWidget", we want 2 drawing colors, a callback list for user input and an `exposeCallback` callback list, and we will declare three convenience procedures, so we need to add

    /* Resources:
    	...
     callback	Callback	Callback	NULL
     drawingColor1	Color	Pixel		XtDefaultForeground
     drawingColor2	Color	Pixel		XtDefaultForeground
     exposeCallback	Callback	Callback	NULL
     font		Font	XFontStruct*	XtDefaultFont
    	...
     */

    #define XtNdrawingColor1 "drawingColor1"
    #define XtNdrawingColor2 "drawingColor2"
    #define XtNexposeCallback "exposeCallback"

    extern Pixel WindowColor1( /* Widget */ );
    extern Pixel WindowColor2( /* Widget */ );
    extern Font  WindowFont( /* Widget */ );

Note that we have chosen to call the input callback list by the generic name, `callback`, rather than a specific name. If widgets that define a single user-input action all choose the same resource name then there is greater possibility for an application to switch between widgets of different types.

# Private Header File

The private header file contains the complete declaration of the class and instance structures for the widget and any additional private data that will be required by anticipated subclasses of the widget. Information in the private header file is normally hidden from the application and is designed to be accessed only through other public procedures; e.g. `XtSetValues`.

The contents of the Template private header file, `<X11/Xaw/TemplateP.h>`, are:

    /* Copyright (c) X Consortium 1987, 1988
     */

    #ifndef _TemplateP_h
    #define _TemplateP_h

    #include <X11/Xaw/Template.h>
    /* include superclass private header file */
    #include <X11/CoreP.h>

    /* define unique representation types not found in <X11/StringDefs.h> */

    #define XtRTemplateResource "TemplateResource"

    typedef struct {
    	int empty;
    } TemplateClassPart;

    typedef struct _TemplateClassRec {
    	CoreClassPart	core_class;
    	TemplateClassPart	template_class;
    } TemplateClassRec;

    extern TemplateClassRec templateClassRec;

    typedef struct {
    	/* resources */
    	char* resource;
    	/* private state */
    } TemplatePart;

    typedef struct _TemplateRec {
    	CorePart	core;
    	TemplatePart	template;
    } TemplateRec;

    #endif /* _TemplateP_h */

The private header file includes the private header file of its superclass, thereby exposing the entire internal structure of the widget. It may not always be advantageous to do this; your own project development style will dictate the appropriate level of detail to expose in each module.

The "WindowWidget" needs to declare two fields in its instance structure to hold the drawing colors, a resource field for the font and a field for the expose and user input callback lists:

    typedef struct {
    	/* resources */
    	Pixel color_1;
    	Pixel color_2;
    	XFontStruct* font;
    	XtCallbackList expose_callback;
    	XtCallbackList input_callback;
    	/* private state */
    	/* (none) */
    } WindowPart;

# Widget Source File

The source code file implements the widget class itself. The unique part of this file is the declaration and initialization of the widget class record structure and the declaration of all resources and action routines added by the widget class.

The contents of the Template implementation file, `<X11/Xaw/Template.c>`, are:

    /* Copyright (c) X Consortium 1987, 1988
     */

    #include <X11/IntrinsicP.h>
    #include <X11/StringDefs.h>
    #include "TemplateP.h"

    static XtResource resources[] = {
    #define offset(field) XtOffsetOf(TemplateRec, template.field)
    	/* {name, class, type, size, offset, default_type, default_addr}, */
        { XtNtemplateResource, XtCTemplateResource, XtRTemplateResource,
    	  sizeof(char*), offset(resource), XtRString, (XtPointer) "default" },
    #undef offset
    };

    static void TemplateAction(/* Widget, XEvent*, String*, Cardinal* */);

    static XtActionsRec actions[] =
    {
    	/* {name,	procedure}, */
    	{"template",	TemplateAction},
    };

    static char translations[] =
    "	<Key>:	template( ) \\n\\
    ";

    TemplateClassRec templateClassRec = {
      { /* core fields */
            /* superclass           */      (WidgetClass) &widgetClassRec,
            /* class_name           */      "Template",
            /* widget_size          */      sizeof(TemplateRec),
            /* class_initialize     */      NULL,
            /* class_part_initialize */     NULL,
            /* class_inited         */      FALSE,
            /* initialize           */      NULL,
            /* initialize_hook      */      NULL,
            /* realize              */      XtInheritRealize,
            /* actions              */      actions,
            /* num_actions          */      XtNumber(actions),
            /* resources            */      resources,
            /* num_resources        */      XtNumber(resources),
            /* xrm_class            */      NULLQUARK,
            /* compress_motion      */      TRUE,
            /* compress_exposure    */      TRUE,
            /* compress_enterleave  */      TRUE,
            /* visible_interest     */      FALSE,
            /* destroy              */      NULL,
            /* resize               */      NULL,
            /* expose               */      NULL,
            /* set_values           */      NULL,
            /* set_values_hook      */      NULL,
            /* set_values_almost    */      XtInheritSetValuesAlmost,
            /* get_values_hook      */      NULL,
            /* accept_focus         */      NULL,
            /* version              */      XtVersion,
            /* callback_private     */      NULL,
            /* tm_table             */      translations,
            /* query_geometry       */      XtInheritQueryGeometry,
            /* display_accelerator  */      XtInheritDisplayAccelerator,
            /* extension            */      NULL
      },
      { /* template fields */
            /* empty                */      0
      }
    };

    WidgetClass templateWidgetClass = (WidgetClass)&templateClassRec;

The resource list for the "WindowWidget" might look like the following:

    static XtResource resources[] = {
    #define offset(field) XtOffsetOf(WindowWidgetRec, window.field)
    	/* {name, class, type, size, offset, default_type, default_addr}, */
    	{ XtNdrawingColor1, XtCColor, XtRPixel, sizeof(Pixel),
    		  offset(color_1), XtRString, XtDefaultForeground },
    	{ XtNdrawingColor2, XtCColor, XtRPixel, sizeof(Pixel),
    		  offset(color_2), XtRString, XtDefaultForeground },
    	{ XtNfont, XtCFont, XtRFontStruct, sizeof(XFontStruct*),
    		  offset(font), XtRString, XtDefaultFont },
    	{ XtNexposeCallback, XtCCallback, XtRCallback, sizeof(XtCallbackList),
    		  offset(expose_callback), XtRCallback, NULL },
    	{ XtNcallback, XtCCallback, XtRCallback, sizeof(XtCallbackList),
    		  offset(input_callback), XtRCallback, NULL },
    #undef offset
    };

The user input callback will be implemented by an action procedure which passes the event pointer as call_data. The action procedure is declared as:

    /* ARGSUSED */
    static void InputAction(w, event, params, num_params)
    	Widget w;
    	XEvent *event;
    	String *params;		/* unused */
    	Cardinal *num_params;	/* unused */
    {
    	XtCallCallbacks(w, XtNcallback, (XtPointer)event);
    }

    static XtActionsRec actions[] =
    {
    	/* {name,	procedure}, */
    	{"input",	InputAction},
    };

and the default input binding will be to execute the input callbacks on `KeyPress` and `ButtonPress :`

    static char translations[] =
    "	<Key>:	input( ) \\n\\
     	<BtnDown>:	input( ) \\
    ";

In the class record declaration and initialization, the only field that is different from the Template is the expose procedure:

    /* ARGSUSED */
    static void Redisplay(w, event, region)
    	Widget w;
    	XEvent *event;	/* unused */
    	Region region;
    {
    	XtCallCallbacks(w, XtNexposeCallback, (XtPointer)region);
    }

    WindowClassRec windowClassRec = {

    	...

    	/* expose	*/	Redisplay,

The "WindowWidget" will also declare three public procedures to return the drawing colors and the font id, saving the application the effort of constructing an argument list for a call to `XtGetValues :`

    Pixel WindowColor1(w)
            Widget w;
    {
            return ((WindowWidget)w)->window.color_1;
    }

    Pixel WindowColor2(w)
            Widget w;
    {
            return ((WindowWidget)w)->window.color_2;
    }

    Font WindowFont(w)
            Widget w;
    {
            return ((WindowWidget)w)->window.font->fid;
    }

The "WindowWidget" is now complete. The application can retrieve the two drawing colors from the widget instance by calling either `XtGetValues`, or the `WindowColor` functions. The actual window created for the "WindowWidget" is available by calling the `XtWindow` function.