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:

• 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, in place

•
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_classSpecifies the widget class pointer for the created widget

offsetReturns the offset record

constraint_offsetReturns the constraint offset record

RELATED INFORMATION

XmResolvePartOffsets(3X). 

Hewlett-Packard Company  —  Motif Release 1.2: May 1992