XmResolveAllPartOffsets(3X) OSF 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)
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 } };
1 (printed 6/8/92)
XmResolveAllPartOffsets(3X) OSF XmResolveAllPartOffsets(3X)
⊕ 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.
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XmResolveAllPartOffsets(3X) OSF XmResolveAllPartOffsets(3X)
#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_class
Specifies the widget class pointer for the created
widget
offset Returns the offset record
constraint_offset
Returns the constraint offset record
RELATED INFORMATION
XmResolvePartOffsets(3X).
3 (printed 6/8/92)