XmResolveAllPartOffsets(3X)XmResolveAllPartOffsets(3X)NAMEXmResolveAllPartOffsets — A function that allows writing of upward-com‐
patible applications and widgets
SYNOPSIS
#include <Xm/XmP.h>
void XmResolveAllPartOffsets (widget_class, offset, constraint_offset)
WidgetClasswidget_class; XmOffsetPtr* offset; XmOff‐
setPtr* constraint_offset;
VERSION
This page documents version 1.2 of the Motif library.
DESCRIPTION
The use of offset records requires two extra global variables per wid‐
get 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 wid‐
get'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 wid‐
get 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 initial‐
ization, 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 con‐
straint offset record. This does several things:
Adds the superclass (which, by definition, has already been initial‐
ized) size field to the part size field
If the widget is a subclass of the Constraint class, adds the super‐
class 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) argu‐
ment, as illustrated here: XmField(w, offset, Label, text, char *) You
can define macros for each field to make this easier. Assume an inte‐
ger field xyz: #define BarXyz(w) (*(int *)(((char *) w) + \ off‐
set[BarIndex] + XtOffset(BarPart,xyz)))
For constraint field max_width: #define BarMaxWidth(w) \ XmCon‐
straintField(w,constraint_offsets,Bar,max_width,Dimension)
The parameters for XmResolveAllPartOffsets are defined below: Specifies
the widget class pointer for the created widget Returns the offset
record Returns the constraint offset record
RELATED INFORMATIONXmResolvePartOffsets(3X).
XmResolveAllPartOffsets(3X)
