XmResolveAllPartOffsets(3X) 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)
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 off-
set 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 struc-
ture 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 con-
straint 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, allo-
cates an array for the constraint offset record. Fills in the offsets of all the widget parts and constraint parts with the appro-
priate 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 exam-
ple, 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: Specifies the widget class pointer for the created widget Returns the offset
record Returns the constraint offset record
SEE ALSO
XmResolvePartOffsets(3X)
XmResolveAllPartOffsets(3X)