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XmResolveAllPartOffsets(3X)
OSF/Motif
NAME
  XmResolveAllPartOffsets - A function that allows writing of upward-
  compatible applications and widgets

SYNOPSIS
  #include <Xm/XmP.h>

  void XmResolveAllPartOffsets (widget_class, offset, constraint_offset)
	  WidgetClass widget_class;
	  XmOffsetPtr * offset;
	  XmOffsetPtr * constraint_offset;

DESCRIPTION
  The use of offset records requires two extra global variables per widget
  class.  The variables consist of pointers to arrays of offsets into the
  widget record and constraint record for each part of the widget structure.
  The XmResolveAllPartOffsets function allocates the offset records needed by
  an application to guarantee upward-compatible access to widget instance and
  constraint records by applications and widgets. These offset records are
  used by the widget to access all of the widget's variables. A widget needs
  to take the following steps:

    ·  Instead of creating a resource list, the widget creates an offset
       resource list. To help you accomplish this, use the XmPartResource
       structure and the XmPartOffset macro. The XmPartResource data
       structure looks just like a resource list, but instead of having one
       integer for its offset, it has two shorts. This is put into the class
       record as if it were a normal resource list.  Instead of using
       XtOffset for the offset, the widget uses XmPartOffset.

       If the widget is a subclass of the Constraint class and it defines
       additional constraint resources, create an offset resource list for
       the constraint part as well. Instead of using XtOffset for the offset,
       the widget uses XmConstraintPartOffset in the constraint resource
       list.

	    XmPartResource resources[] = {
	      {	 BarNxyz, BarCXyz, XmRBoolean, sizeof(Boolean),
		 XmPartOffset(Bar,xyz), XmRImmediate, (XtPointer)False } };

	    XmPartResource constraints[] = {
	      {	 BarNmaxWidth, BarNMaxWidth,
		      XmRDimension, sizeof(Dimension),
		      XmConstraintPartOffset(Bar,max_width),
		      XmRImmediate, (XtPointer)100 } };

    ·  Instead of putting the widget size in the class record, the widget
       puts the widget part size in the same field. If the widget is a
       subclass of the Constraint class, instead of putting the widget
       constraint record size in the class record, the widget puts the widget
       constraint part size in the same field.

    ·  Instead of putting XtVersion in the class record, the widget puts
       XtVersionDontCheck in the class record.

    ·  Define a variable, of type XmOffsetPtr, to point to the offset record.
       If the widget is a subclass of the Constraint class, define a variable
       of type XmOffsetPtr to point to the constraint offset record. These
       can be part of the widget's class record or separate global variables.

    ·  In class initialization, the widget calls XmResolveAllPartOffsets,
       passing it pointers to the class record, the address of the offset
       record, and the address of the constraint offset record. If the widget
       not is a subclass of the Constraint class, it should pass NULL as the
       address of the constraint offset record. This does several things:

	 -- Adds the superclass (which, by definition, has already been
	    initialized) size field to the part size field.

	 -- If the widget is a subclass of the Constraint class, adds the
	    superclass constraint size field to the constraint size field.

	 -- Allocates an array based upon the number of superclasses.

	 -- If the widget is a subclass of the constraint class, allocates an
	    array for the constraint offset record.

	 -- Fills in the offsets of all the widget parts and constraint parts
	    with the appropriate values, determined by examining the size
	    fields of all superclass records.

	 -- Uses the part offset array to modify the offset entries in the
	    resource list to be real offsets.

    ·  The widget defines a constant which will be the index to its part
       structure in the offsets array. The value should be 1 greater than the
       index of the widget's superclass. Constants defined for all Xm widgets
       can be found in <XmP.h>.

	    #define BarIndex (XmBulletinBIndex + 1)

    ·  Instead of accessing fields directly, the widget must always go
       through the offset table. The XmField and XmConstraintField macros
       help you access these fields. Because the XmPartOffset,
       XmConstraintPartOffset, XmField, and XmConstraintField macros
       concatenate things together, you must ensure that there is no space
       after the part argument.	 For example, the following macros do not
       work because of the space after the part (Label) argument:

	    XmField(w, offset, Label , text, char *)
	    XmPartOffset(Label , text).

       Therefore, you must not have any spaces after the part (Label)
       argument, as illustrated here:

	    XmField(w, offset, Label, text, char *)

       You can define macros for each field to make this easier. Assume an
       integer field xyz:

	    #define BarXyz(w) (*(int *)(((char *) w) + \
	      offset[BarIndex] + XtOffset(BarPart,xyz)))

       For constraint field max_width:

	    #define BarMaxWidth(w) \
	      XmConstraintField(w,constraint_offsets,Bar,max_width,Dimension)

  The parameters for XmResolveAllPartOffsets are defined below:

  widget_class
      Specifies the widget class pointer for the created widget

  offset
      Returns the offset record

  constraint_offset
      Returns the constraint offset record

SEE ALSO
  XmResolvePartOffsets(3X)

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