(3)

NAME
XfwfCommon

DESCRIPTION
The Common class is not meant to be instantiated. It only serves as the common superclass for a family of widgets, to ensure that these widgets have some common methods and resources. The Common class defines common types, symbolic constants, and type converters and it also provides the basis for keyboard traversal. The code for keyboard traversal is roughly based on that in the Xw widget set (created by Hewlett Packard), but it uses the accept_focus method. When the resource traversalOn is set to True (either at creation time, or via a XtSetValues later), a set of translations is added to the widget. If the widget's parent is also a subclass of Common, these translations will then implement keyboard traversal, using the cursor keys (up, down, prev, etc.) Of course, when the widget already uses these keys for other purposes, the keyboard traversal will not work.

  Public variables
XfwfCommon
Name | Class | Type | Default
XtNtraversalOn | XtCTraversalOn | Boolean | True
XtNhighlightThickness | XtCHighlightThickness | Dimension | 2
XtNhighlightColor | XtCHighlightColor | Pixel | XtDefaultForeground
XtNhighlightPixmap | XtCHighlightPixmap | Pixmap | None
XtNnextTop | XtCNextTop | Callback | NULL
XtNuserData | XtCUserData | Pointer | NULL

XtNtraversalOn
    The resource traversalOn determines whether keyboard traversal is used. If it is True initially, or if it is set to True later, a set of translations will be added to the widget.

    Boolean  traversalOn = True

XtNhighlightThickness
    Keyboard focus is indicated by border highlighting. When keyboard traversal is on and the widget receives the focus, the highlight border is filled with the highlight color or tile. If the widget does not have the focus, the area is left in the default background.

    Dimension  highlightThickness = 2

XtNhighlightColor
    The highlight border can have a color or it can be tiled with a pixmap. Whichever of the resources highlightColor or highlightPixmap is set latest, is used. When both are set, the pixmap is used.

    Pixel  highlightColor = <String>XtDefaultForeground

XtNhighlightPixmap
    The highlightPixmap can be set to a pixmap with which the highlight border will be tiled. Only one of highlightPixmap and highlightColor can be set, see above.

    Pixmap  highlightPixmap = None

XtNnextTop
    When an application has several top level windows, it should have a way of setting the focus between windows. The Enter key in any widget with keyboard traversal on normally invokes the traverseNextTop action, that will call the callbacks of the topmost Common (or subclass) widget in the hierarchy. The callback may set the focus to another top level widget, with XtCallAcceptFocus.

    <Callback> XtCallbackList  nextTop = NULL

XtNuserData
    The resource userData is provided for applications that want to attach their own data to a widget. It is not used by the widget itself in any way.

    <Pointer> XtPointer  userData = NULL
    Composite
    Name | Class | Type | Default
    XtNchildren | XtCChildren | WidgetList | NULL
    insertPosition | XtCInsertPosition | XTOrderProc | NULL
    numChildren | XtCNumChildren | Cardinal | 0
    Core
    Name | Class | Type | Default
    XtNx | XtCX | Position | 0
    XtNy | XtCY | Position | 0
    XtNwidth | XtCWidth | Dimension | 0
    XtNheight | XtCHeight | Dimension | 0
    borderWidth | XtCBorderWidth | Dimension | 0
    XtNcolormap | XtCColormap | Colormap | NULL
    XtNdepth | XtCDepth | Int | 0
    destroyCallback | XtCDestroyCallback | XTCallbackList | NULL
    XtNsensitive | XtCSensitive | Boolean | True
    XtNtm | XtCTm | XTTMRec | NULL
    ancestorSensitive | XtCAncestorSensitive | Boolean | False
    accelerators | XtCAccelerators | XTTranslations | NULL
    borderColor | XtCBorderColor | Pixel | 0
    borderPixmap | XtCBorderPixmap | Pixmap | NULL
    background | XtCBackground | Pixel | 0
    backgroundPixmap | XtCBackgroundPixmap | Pixmap | NULL
    mappedWhenManaged | XtCMappedWhenManaged | Boolean | True
    XtNscreen | XtCScreen | Screen * | NULL

  Exports
The type Alignment is actually an integer, but it is given a different name to allow a type converter to be installed for it.

type
 Alignment = int
The symbolic constants can be added together to form an alignment. Various widgets use this to position labels, other widgets, etcetera.

def XfwfCenter = 0 def XfwfLeft = 1 def XfwfRight = 2 def XfwfTop = 4 def XfwfBottom = 8 For convenience, the eight possible combinations also have symbolic names.

def XfwfTopLeft = (XfwfTop +XfwfLeft ) def XfwfTopRight = (XfwfTop +XfwfRight ) def XfwfBottomLeft = (XfwfBottom +XfwfLeft ) def XfwfBottomRight = (XfwfBottom +XfwfRight ) The directions of traversal are used as arguments to the traverse method. They are probably only useful to subclasses.

type
 TraversalDirection = enum {
	    TraverseLeft, TraverseRight, TraverseUp, TraverseDown,
	    TraverseNext, TraversePrev, TraverseHome, TraverseNextTop }
To know the inside area of a Common widget might be useful to other widgets than subclasses alone. Calling XfwfCallComputeInside will call the compute_inside method, if available.
XfwfCallComputeInside( $, Position * x, Position * y, Dimension * w, Dimension * h)
{
    if (XtIsSubclass($, xfwfCommonWidgetClass) $compute_inside)
    $compute_inside($, x, y, w, h); }

  Actions
When the widget receives or looses the focus, the border highlight is drawn or removed. This action function draws the highlight border and in case the widget has set traversalOn, it also sets the keyboard focus to the widget itself, or one of its children. However, FocusIn events may also be so-called virtual events, meaning that not the receiving widget, but one of its descendants gets the real focus. When focusIn receives one of those, it removes the highlight border. def focus_detail(detail) = (detail ==NotifyAncestor ?"NotifyAncestor":detail ==NotifyVirtual ?"NotifyVirtual":detail ==NotifyInferior ?"NotifyInferior":detail ==NotifyNonlinear ?"NotifyNonlinear":detail ==NotifyNonlinearVirtual ?"NotifyNonlinearVirtual":detail ==NotifyPointer ?"NotifyPointer":detail ==NotifyPointerRoot ?"NotifyPointerRoot":detail ==NotifyDetailNone ?"NotifyDetailNone":"???")

focusIn
    void focusIn($, XEvent* event, String* params, Cardinal* num_params)
    {
        Time time = CurrentTime;
        if (event->type != FocusIn)
    	XtError("focusIn action may only be bound to FocusIn events");
        if (! $traversalOn)
    	return;
        if (event->xfocus.detail == NotifyAncestor
    	|| event->xfocus.detail == NotifyInferior
    	|| event->xfocus.detail == NotifyNonlinear) {
    	if (! $traversal_focus) (void) $accept_focus($, time);
        } else if ($traversal_focus) {
    	$unhighlight_border($);
    	$traversal_focus = False;
        }
    }

focusOut
    This action removes the highlight border.
    void focusOut($, XEvent* event, String* params, Cardinal* num_params)
    {
        if (event->type != FocusOut)
    	XtError("focusOut action may only be bound to FocusOut events");
        if ($traversal_focus) {
    	$unhighlight_border($);
    	$traversal_focus = False;
        }
    }

traverseDown
    This and the following actions all call the traverse method of the widget's parent, with the appropriate direction arguments. traverseDown tries to set the focus to a widget that is located roughly below the current one.
    void traverseDown($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseDown, $, event->xkey.time);
    }

traverseUp
    The action tries to set the focus to a widget that is above the this one.
    void traverseUp($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseUp, $, event->xkey.time);
    }

traverseLeft
    traverseLeft looks for a widget to the left of the current one and sets the keyboard focus to that.
    void traverseLeft($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseLeft, $, event->xkey.time);
    }

traverseRight
    The action looks for a widget that will aceept the focus to the right of the current one.
    void traverseRight($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseRight, $, event->xkey.time);
    }

traverseNext
    The next sibling gets the focus. The precise order is determined by the parent, but usually is will be the order in which the widgets were created. If there is no suitable sibling, the request is passed to the grandparent, so that an `aunt widget' or other relation can get the focus.
    void traverseNext($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseNext, $, event->xkey.time);
    }

traversePrev
    The previous widget gets the focus. See also the description of traverseNext above.
    void traversePrev($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraversePrev, $, event->xkey.time);
    }

traverseNextTop
    traverseNextTop finds the topmost ancestor that is a subclass of Common and lets it call the nextTop callbacks that have been registered there. These callbacks can be used by an application that has multiple top level windows to set the focus to another window.
    void traverseNextTop($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseNextTop, $, event->xkey.time);
    }

traverseHome
    The action sets the focus to the sibling widget that is closest to the upper left corner of the parent.
    void traverseHome($, XEvent* event, String* params, Cardinal* num_params)
    {
        $traverse($, TraverseHome, $, event->xkey.time);
    }

traverseCurrent
    The traverseCurrent action can be used by widgets to set the focus to themselves. It is not used in the set of translations that is added when traversalOn is set to True.
    void traverseCurrent($, XEvent* event, String* params, Cardinal* num_params)
    {
        Time time = CurrentTime;
        if ($traversalOn) (void) $accept_focus($, time);
    }

Importss
Most of the included files have to do with the Icon type. Six icons are preloaded.
incl
 <stdio.h>
incl
 <X11/Xmu/Converters.h>
incl
 <Xfwf/Converters.h>

  Private variables
abs, min and max are used often enough in various subclasses to define them here. They will end up in the private(!) header file.

 max
 min
 abs
A private variable is used to track the keyboard focus, but only while traversal is on. If traversal_focus is True, it means that the widget has keyboard focus and that that focus is a result of keyboard traversal. It also means that the widget's border is highlighted, although that is only visible if the highlightThickness is positive.

Boolean  traversal_focus
The highlight border is filled with a color or a tile.

GC  bordergc

Class variables
traversal_trans holds the compiled version of the extraTranslations.

XtTranslations  traversal_trans = NULL

  Methods
The type converter cvtStringToAlignment is installed in the class_initialize method, after the quarks for the recognized strings are created. The converter from String to Icon needs one extra argument, viz., the widget for which the icon is loaded. An offset of 0 should give a pointer to the widget itself.
class_initialize()
{
    static XtConvertArgRec args[] = {
    { XtWidgetBaseOffset, 0, sizeof(Widget) } };
    XtSetTypeConverter(XtRString, "Alignment", cvtStringToAlignment,
		       NULL, 0, XtCacheNone, NULL);
    XtSetTypeConverter("Alignment", XtRString, cvtAlignmentToString,
		       NULL, 0, XtCacheNone, NULL);
    /* init_icon_quarks(); */
    XtSetTypeConverter(XtRString, "Icon", cvtStringToIcon,
		       args, XtNumber(args), XtCacheNone, NULL);
}
The extraTranslations are compiled into Xt's internal form and stored in a class variable traversal_trans, but only if that hasn't been done before. (It should have been done in the class_initialize method, but wbuild's `$' syntax doesn't work there (yet)). If the widget has the traversalOn resource set, the translations are merged with the widgets existing translations.
initialize(Widget  request, $, ArgList  args, Cardinal * num_args)
{
    if ($traversal_trans == NULL)
	$traversal_trans = XtParseTranslationTable(extraTranslations);
    if ($traversalOn) {
	XtAugmentTranslations($, $traversal_trans);
	$visible_interest = True;
    }
    $traversal_focus = False;
    $bordergc = NULL;
    create_bordergc($);
}
The set_values method checks if the keyboard traversal has been turned on and adds the traversal translations. (It can only be turned on, not turned off.) If something changes that causes the widget to loose keyboard focus, the parent is asked to put the focus somewhere else. Otherwise the whole application might suddenly loose keyboard focus.
Boolean  set_values(Widget  old, Widget  request, $, ArgList  args, Cardinal * num_args)
{
    Boolean need_redraw = False;
    Widget parent = XtParent($);
    Time time = CurrentTime;
    if ($traversalOn != $old$traversalOn  $traversalOn) {
	XtAugmentTranslations($, $traversal_trans);
	$visible_interest = True;
    }
    if (($sensitive != $old$sensitive
	 || $ancestor_sensitive != $old$ancestor_sensitive
	 || $traversalOn != $old$traversalOn)
	 $traversal_focus) {
	if (XtIsSubclass(parent, xfwfCommonWidgetClass))
	    $parent$traverse(parent, TraverseHome, $, time);
    }
    if ($highlightThickness != $old$highlightThickness)
	need_redraw = True;
    if ($highlightPixmap != $old$highlightPixmap) {
	create_bordergc($);
	need_redraw = True;
    } else if ($highlightColor != $old$highlightColor) {
	$highlightPixmap = None;
	create_bordergc($);
	need_redraw = True;
    }
    return need_redraw;
}
A new method compute_inside is defined, that returns the area inside the highlight border. Subclasses should use this to compute their drawable area, in preference to computing it from $width and $height. Subclasses, such as the Frame widget, redefine the method if they add more border material.
compute_inside($, Position * x, Position * y, Dimension * w, Dimension * h)
{
    *x = $highlightThickness;
    *y = $highlightThickness;
    *w = $width - 2 * $highlightThickness;
    *h = $height - 2 * $highlightThickness;
}
The expose method draws the highlight border, if there is one.
expose($, XEvent * event, Region  region)
{
    if (! XtIsRealized($)) return;
    if (region != NULL) XSetRegion(XtDisplay($), $bordergc, region);
    if ($traversal_focus) $highlight_border($);
    if (region != NULL) XSetClipMask(XtDisplay($), $bordergc, None);
}
When the widget is destroyed and the widget still has the keyboard focus, the parent is asked to give it to another widget.
destroy($)
{
    Widget parent = XtParent($);
    Time time = CurrentTime;
    if ($traversal_focus) {
	$sensitive = False;
	if (XtIsSubclass(parent, xfwfCommonWidgetClass))
	    $parent$traverse(parent, TraverseHome, $, time);
    }
}
The border highlight is drawn and removed with two methods, although few subclasses will want to redefine them. The methods are called by the focusIn and focusOut actions and highlight_border is also called by expose.
highlight_border($)
{
    XRectangle rect[4];
    if ($highlightThickness == 0) return;
    rect[0].x = 0;
    rect[0].y = 0;
    rect[0].width = $width;
    rect[0].height = $highlightThickness;
    rect[1].x = 0;
    rect[1].y = 0;
    rect[1].width = $highlightThickness;
    rect[1].height = $height;
    rect[2].x = $width - $highlightThickness;
    rect[2].y = 0;
    rect[2].width = $highlightThickness;
    rect[2].height = $height;
    rect[3].x = 0;
    rect[3].y = $height - $highlightThickness;
    rect[3].width = $width;
    rect[3].height = $highlightThickness;
    XFillRectangles(XtDisplay($), XtWindow($), $bordergc, rect[0], 4);
}
unhighlight_border($)
{
    if ($highlightThickness == 0) return;
    XClearArea(XtDisplay($), XtWindow($),
	       0, 0, $width, $highlightThickness, False);
    XClearArea(XtDisplay($), XtWindow($),
	       0, 0, $highlightThickness, $height, False);
    XClearArea(XtDisplay($), XtWindow($),
	       $width - $highlightThickness, 0,
	       $highlightThickness, $height, False);
    XClearArea(XtDisplay($), XtWindow($),
	       0, $height - $highlightThickness,
	       $width, $highlightThickness, False);
}
When the accept_focus method is called, the widget should try to set the focus to itself or one of its children. If it succeeds, it returns True else False. If there are children, each is asked in turn, until one is found that accepts the focus. If none is found, the widget checks it's own sensitive resource, to see if it can receive keyboard events. If so, it sets the focus to itself and returns True, otherwise False.
Boolean  accept_focus($, Time * time)
{
    int i;
    if (! XtIsRealized($) || ! $sensitive || ! $traversalOn
	|| ! $visible || ! $ancestor_sensitive || ! $managed
	|| ! $mapped_when_managed || $being_destroyed) return False;
    for (i = 0; i < $num_children; i++)
        if (XtCallAcceptFocus($children[i], time)) return True;
    if (! $traversal_focus) {
	XSetInputFocus(XtDisplay($), XtWindow($), RevertToParent, *time);
	$traversal_focus = True;
	$highlight_border($);
    }
    return True;
}
A Common widget (and most subclasses) return True for would_accept_focus, if the sensitive, visible and traversalOn resources are set and none of the children wants the focus.
Boolean  would_accept_focus($)
{
    int i;
    Widget child;
    if (! XtIsRealized($) || ! $sensitive || ! $visible || ! $traversalOn)
        return False;
    else {
        for (i = 0; i < $num_children; i++) {
            child = $children[i];
            if (XtIsSubclass(child, xfwfCommonWidgetClass)
                 $child$would_accept_focus(child))
                return False;
	}
        return True;
    }
}
The algorithm behind keyboard traversal * Handling focus events If a widget receives a (non-virtual) FocusIn event, this is usually caused by the accept_focus method of that widget, except in the case that a top level widget receives the focus from the window manager. In the first case, the window can just draw the highlight border, in the second case, the widget should try to set the focus to one of its children. To be able to distinguish the two cases, the accept_focus method sets the private instance variable traversal_focus to True before it calls XSetInputFocus. The focusIn action then checks this variable and if it is not set, calls the accept_focus method. The focusOut action resets traversal_focus to False. The traversal_focus variable can be interpreted to mean, that the widget has the keyboard focus and that it is because of keyboard traversal. At least in the Common widget, it can never be True when traversalOn is not set. It can also only be True when the widget actually has the focus, except in the short time between the XSetInputFocus call and the delivery of the FocusIn event. (However, this scheme depends on the focusOut action for resetting traversal_focus to False, so, if the translation for the FocusOut event is overridden, it will break down.) * User events The traverseXXX actions can be bound to keyboard events. They call the traverse method, which will try to change the focus in the indicated direction. The directions are: Home, Up, Left, Down, Right, Next, Prev. Each direction can be considered a constraint or criterium for choosing the focus widget, e.g., `Up' selects the nearest widget that is above the current widget. `Next' and `Prev' are simpler, in that they do not check the distance, but only the order in the list of children. The traverseCurrent action is different. It is usually bound to a mouse click and its task is to set the focus to the widget itself. It does this by calling accept_focus on itself. The traverse method looks for a widget in the indicated direction, within the same application. If the direction is not `Next' or `Prev', the method first recurses upwards, to the toplevel widget. From there it recurses down again, to all children, grandchildren, etc., looking for the widget that best matches the criterium. If a widget is found, the focus will be set to it with a call to XSetInputFocus. The private variable traversal_focus will be set to True to indicate that the widget received the focus as a result of keyboard traversal, and not from the window manager or any other source. If the direction argument is `Next' or `Prev', traverse will try to set the focus to a sister widget, using the accept_focus method. If there is no suitable sister, the parent will be asked to find an aunt widget, and so on. Note that the traverse and accept_focus methods of the Common widget only set the focus to a child, if the widget itself has traversalOn. Thus, setting traversalOn to False for a certain widget not only excludes the widget itself from keyboard traversal, but also all its children. The traverse function is a method and not a utility function, because it is expected that a few subclasses may want to redefine it. E.g., the (not yet existing) Group widget may want to limit traversal to widgets within itself. (And presumably define new actions to jump outside the group.) To check if a widget suits the criterium, two things must be determined: is the widget eligible for the focus and what is the distance between the widget and the target position. To be able to determine if the widget can accept the focus without actually setting it, a method would_accept_focus is defined, that returns True if the widget is willing to set the focus to itself. If the dir argument to traverse is TraverseNext or TraversePrev, the traverse_to_next or traverse_to_prev utility functions are called. Otherwise, the traverse method checks the class of the parent. If the parent is a subclass of XfwfCommon, it also has a traverse method and the task of finding a widget to traverse to is delegated to the parent. Otherwise, the desired widget is looked for with the help of a utility function. The dir argument is one of Home, Up, Down, Left, Right, Next or Prev. The current argument holds the widget that currently has the focus and relative to which the focus will have to move. def LARGE_NUMBER = 2000000000
traverse($, TraversalDirection  dir, Widget  current, Time * time)
{
    Widget w, parent = XtParent($);
    Position x, y;
    int distance = LARGE_NUMBER;
    if (dir == TraverseNextTop)
	traverse_to_next_top($, current, time);
    else if (dir == TraverseNext)
        traverse_to_next($, current, time);
    else if (dir == TraversePrev)
        traverse_to_prev($, current, time);
    else if (XtIsSubclass(parent, xfwfCommonWidgetClass))
        $parent$traverse(parent, dir, current, time);
    else {
        switch (dir) {
        case TraverseHome: x = 0; y = 0; break;
        case TraverseLeft: x = 0; y = $current$height/2; break;
        case TraverseDown: x = $current$width/2; y = $current$height; break;
        case TraverseRight: x = $current$width; y = $current$height/2; break;
        case TraverseUp: x = $current$width/2; y = 0; break;
        }
        if (dir != TraverseHome) XtTranslateCoords(current, x, y, x, y);
        if (traverse_to_direction($, dir, x, y, w, distance))
            XtCallAcceptFocus(w, time);
    }
}
To choose a color that is somewhat darker or lighter than another color, the function choose_color queries the RGB values of a pixel and multiplies them with a factor. If all goes well, the function returns True. If the chosen color ends up being the same as the original, the color gray75 is returned instead. It is defined as a method, to make it accessible to subclasses. There seems to be no need to make it available globally.
Boolean  choose_color($, double  factor, Pixel  base, Pixel * result)
{
    XColor color1, color2, dummy;
    color1.pixel = base;
    XQueryColor(XtDisplay($), DefaultColormapOfScreen(XtScreen($)), color1);
    color2.red = min(65535, factor * color1.red);
    color2.green = min(65535, factor * color1.green);
    color2.blue = min(65535, factor * color1.blue);
    if (! XAllocColor(XtDisplay($),
		      DefaultColormapOfScreen(XtScreen($)), color2))
	return False;
    if (base == color2.pixel) {
	if (! XAllocNamedColor(XtDisplay($),
			       DefaultColormapOfScreen(XtScreen($)), "gray75",
			       color2, dummy))
	    return False;
    }
    *result = color2.pixel;
    return True;
}
The method lighter_color uses choose_color to compute a color that is 1.5 times as bright as the color passed in as argument. The function result is True if a color was allocated, else False.
Boolean  lighter_color($, Pixel  base, Pixel * result)
{
    return choose_color($, 1.5, base, result);
}
The method darker_color uses choose_color to compute a color that is 2/3 times as bright as the color passed in as argument. The function result is True if a color was allocated, else False.
Boolean  darker_color($, Pixel  base, Pixel * result)
{
    return choose_color($, 0.667, base, result);
}

Utilities
The converter cvtStringToAlignment converts strings like `right', `top left' and `bottom center' to values of type Alignment. def done(type, value) = do {
    if (to->addr != NULL) {
        if (to->size < sizeof(type)) {
            to->size = sizeof(type);
            return False;
        }
        *(type*)(to->addr) = (value);
        } else {
        static type static_val;
        static_val = (value);
        to->addr = (XtPointer)static_val;
        }
        to->size = sizeof(type);
        return True;
    }while (0 )
Boolean  cvtStringToAlignment(Display * display, XrmValuePtr  args, Cardinal * num_args, XrmValuePtr  from, XrmValuePtr  to, XtPointer * converter_data)
{
    Alignment a = 0;
    char c, *t, *s = (char*) from->addr;
    if (*num_args != 0)
	XtAppErrorMsg(XtDisplayToApplicationContext(display),
		      "cvtStringToAlignment", "wrongParameters",
		      "XtToolkitError",
		      "String to Alignment conversion needs no arguments",
		      (String*) NULL, (Cardinal*) NULL);
    while (*s) {
	for (; isspace(*s); s++) ;
	for (t = s; *t  ! isspace(*t); t++) ;
	c = *t;
	*t = '\0';
	if (XmuCompareISOLatin1(s, "top") == 0) a |= XfwfTop;
	else if (XmuCompareISOLatin1(s, "bottom") == 0) a |= XfwfBottom;
	else if (XmuCompareISOLatin1(s, "center") == 0) ; /* skip */
	else if (XmuCompareISOLatin1(s, "left") == 0) a |= XfwfLeft;
	else if (XmuCompareISOLatin1(s, "right") == 0) a |= XfwfRight;
	else {
	    XtDisplayStringConversionWarning(display, (char*) from->addr,
					     "Alignment");
	    break;
	}
	*t = c;
	s = t;
    }
    done(Alignment, a);
}
The converter cvtAlignmentToString does the reverse: it convertes values of type Alignment (int's) to strings.
Boolean  cvtAlignmentToString(Display * display, XrmValuePtr  args, Cardinal * num_args, XrmValuePtr  from, XrmValuePtr  to, XtPointer * converter_data)
{
    Alignment *a = (Alignment*) from->addr;
    if (*num_args != 0)
	XtAppErrorMsg(XtDisplayToApplicationContext(display),
		      "cvtAlignmentToString", "wrongParameters",
		      "XtToolkitError",
		      "Alignment to String conversion needs no arguments",
		      (String*) NULL, (Cardinal*) NULL);
    switch (*a) {
    case XfwfCenter: done(String, "center");
    case XfwfBottom: done(String, "bottom");
    case XfwfTop: done(String, "top");
    case XfwfLeft: done(String, "left");
    case XfwfRight: done(String, "right");
    case XfwfBottom + XfwfLeft: done(String, "bottom left");
    case XfwfBottom + XfwfRight: done(String, "bottom right");
    case XfwfTop + XfwfLeft: done(String, "top left");
    case XfwfTop + XfwfRight: done(String, "top right");
    default: done(String, "unknown");
    }
}
The following string is the set of translations that will be added to any widget that has traversalOn set to True. The string is compiled into Xt's internal representation by the class_initialize method.
char  extraTranslations[] = "\
	<FocusIn>: focusIn()\n\
	<FocusOut>: focusOut()\n\
	<Key>Up: traverseUp()\n\
	<Key>Down: traverseDown()\n\
	<Key>Left: traverseLeft()\n\
	<Key>Right: traverseRight()\n\
	<Key>Next: traverseNext()\n\
	~Shift<Key>Tab: traverseNext()\n\
	<Key>Prior: traversePrev()\n\
	Shift<Key>Tab: traversePrev()\n\
	<Key>KP_Enter: traverseNextTop()\n\
	<Key>Home: traverseHome()"
The create_bordergc function creates a new GC for filling the highlight border with.
create_bordergc($)
{
    XtGCMask mask;
    XGCValues values;
    if ($bordergc) XtReleaseGC($, $bordergc);
    if ($highlightPixmap != None) {
	mask = GCFillStyle | GCTile;
	values.fill_style = FillTiled;
	values.tile = $highlightPixmap;
    } else {
	mask = GCFillStyle | GCForeground;
	values.fill_style = FillSolid;
	values.foreground = $highlightColor;
    }
    $bordergc = XtGetGC($, mask, values);
}
The traverse_to_direction function returns the nearest child, grandchild, etc. in the indicated direction that is willing to accept the focus. It returns False if no widget is found. The position is the absolute coordinates, i.e., relative to the root window. The distance argument holds the distance from x,y of the best widget so far. If the function finds a better one, it will return the new distance through this parameter.
Boolean  traverse_to_direction($, TraversalDirection  dir, int  x, int  y, Widget * found, int * distance)
{
    int i;
    Widget child, w;
    Position rx, ry;
    int dist;
    Boolean found_child = False;
    if (! $traversalOn) return False;
    /*
     * First recurse to all descendants
     */
    for (i = 0; i < $num_children; i++)
        if (XtIsSubclass($children[i], xfwfCommonWidgetClass)
             traverse_to_direction($children[i], dir, x, y, found, distance))
            found_child = True;
    if (found_child) return True;
    /*
     * No child found, now check own position and distance
     */
    switch (dir) {
    case TraverseHome: rx = 0; ry = 0; break;
    case TraverseLeft: rx = $width; ry = $height/2; break;
    case TraverseDown: rx = $width/2; ry = 0; break;
    case TraverseRight: rx = 0; ry = $height/2; break;
    case TraverseUp: rx = $width/2; ry = $height; break;
    }
    XtTranslateCoords($, rx, ry, rx, ry);
    if ((dir == TraverseUp  ry > y)
        || (dir == TraverseLeft  rx > x)
        || (dir == TraverseDown  ry < y)
        || (dir == TraverseRight  rx < x)) return False;
    dist = (rx - x)*(rx - x) + (ry - y)*(ry - y);
    if (dist >= *distance) return False;
    /*
     * We are the best so far, but do we want the focus?
     */
    if (! $would_accept_focus($)) return False;
    *distance = dist;
    *found = $;
    return True;
}
The traverse_to_next routine looks for the current widget among its children. If it is found, all children following it will be tried until one accepts the focus. If no child does, the routine will try to ask the parent to find a sister widget instead.
traverse_to_next($, Widget  current, Time * time)
{
    int i = 0;
    Widget parent = XtParent($);
    while (i < $num_children  $children[i] != current) i++;
    for (i++; i < $num_children; i++)
        if (XtCallAcceptFocus($children[i], time)) return;
    if (XtIsSubclass(parent, xfwfCommonWidgetClass))
        $parent$traverse(parent, TraverseNext, $, time);
}
traverse_to_prev looks for the current widget among the children, if it is found, all children before it will be asked in turn to accept the focus. If none does, the parent is asked to set the focus to a sister instead.
traverse_to_prev($, Widget  current, Time * time)
{
    int i = 0;
    Widget parent = XtParent($);
    while (i < $num_children  $children[i] != current) i++;
    for (i--; i >= 0; i--)
        if (XtCallAcceptFocus($children[i], time)) return;
    if (XtIsSubclass(parent, xfwfCommonWidgetClass))
        $parent$traverse(parent, TraversePrev, $, time);
}
traverse_to_next_top($, Widget  current, Time * time)
{
    Widget parent = XtParent($);
    if (XtIsSubclass(parent, xfwfCommonWidgetClass))
	$parent$traverse(parent, TraverseNextTop, current, time);
    else
	XtCallCallbackList($, $nextTop, NULL);
}