XmeResolvePartOffsets(3X) UNIX System V XmeResolvePartOffsets(3X)
NAME
XmeResolvePartOffsets - Allows writing of upward-compatible
applications and widgets
SYNOPSIS
#include <Xm/XmP.h>
void XmeResolvePartOffsets(
WidgetClass widget_class,
XmOffsetPtr *offset,
XmOffsetPtr *constraint_offset);
VERSION
This page documents Motif 2.1.
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 XmeResolvePartOffsets 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 steps described in the following
paragraphs.
Instead of creating a resource list, the widget creates an
offset resource list. To accomplish this, use the
XmPartResourcestructure 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 structure 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
XmConstraintPartOffsetin the constraint resource list.
Do not create parts that do not preserve alignment (for
example, a widget part containing a single Boolean).
XmPartResource resources[] = {
{ BarNxyz, BarCXyz, XmRBoolean, sizeof(Boolean),
XmPartOffset(Bar,xyz), XmRImmediate, (XtPointer)False } };
XmPartResource constraints[] = {
{ BarNmaxWidth, BarNMaxWidth,
XmRDimension, sizeof(Dimension),
XmConstraintPartOffset(Bar,max_width),
Page 1 (printed 7/20/06)
XmeResolvePartOffsets(3X) UNIX System V XmeResolvePartOffsets(3X)
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
XmeResolvePartOffsets, passing it pointers to the class
record, the address of the offset record, and the address of
the constraint offset record. If the widget is not a
subclass of the Constraint class, it should pass NULL as the
address of the Constraint offset record. This does several
things:
o Adds the superclass (which, by definition, has already
been initialized) size field to the part size field
o If the widget is a subclass of the Constraint class,
adds the superclass constraint size field to the
constraint size field
o Allocates an array based upon the number of
superclasses
o If the widget is a subclass of the Constraint class,
allocates an array for the constraint offset record
o Fills in the offsets of all the widget parts and
constraint parts with the appropriate values, which
can be determined by examining the size fields of all
superclass records
o 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 that 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 header
Page 2 (printed 7/20/06)
XmeResolvePartOffsets(3X) UNIX System V XmeResolvePartOffsets(3X)
file Xm/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 XmConstraintFieldmacros concatenate things, 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).
You must not have any spaces after the part (Label)
argument, illustrated as follows:
XmField(w, offset, Label, text, char *)
XmPartOffset(Label, text).
You can define macros for each field to make this easier.
For example, the following shows how to define a macro for
an enumerated field xyz in widget Bar:
#define BarXyz(w) \
XmField(w,offsets,Bar,xyz,XtEnum)
Define a macro for constraint field max_width as follows:
#define BarMaxWidth(w) \
XmConstraintField(w,constraint_offsets,Bar,max_width,Dimension)
The arguments for XmeResolvePartOffsets are as follows:
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
XmResolveAllPartOffsets(3).
Page 3 (printed 7/20/06)
