XmResolveAllPartOffsets(3X)

     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)
               WidgetClasswidget_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:

          o    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 } };

          o    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.

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

          o    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.

          o    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, in place

          o    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)

          o    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

     RELATED INFORMATION
          XmResolvePartOffsets(3X).