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)
WidgetClass widget_class;
XmOffsetPtr * offset;
XmOffsetPtr * constraint_offset;
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 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 con‐
straint part size in the same field. Instead of putting XtVer‐
sion 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 wid‐
get's class record or separate global variables. In class ini‐
tialization, 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 super‐
class 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 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,Dimen‐
sion)
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 ALSOXmResolvePartOffsets(3X)XmResolveAllPartOffsets(3X)
