XmResolvePartOffsets(3Xm) XmResolvePartOffsets(3Xm)
NAME
XmResolvePartOffsets - a function that allows writing
of upward-compatible applications and widgets.
AES SUPPORT LEVEL
full-use
SYNOPSIS
#include <Xm/XmP.h>
void XmResolvePartOffsets (widget_class, offset)
WidgetClasswidget_class;
XmOffsetPtr* offset;
DESCRIPTION
The use of offset records requires one extra global
variable per widget class. The variable consists of a
pointer to an array of offsets into the widget record
for each part of the widget structure. The
XmResolvePartOffsets function allocates the offset
records needed by an application to guarantee upward-
compatible 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 gets put into the class record as
if it were a normal resource list. Instead of using
XtOffset for the offset, it uses XmPartOffset.
⊕ Instead of putting the widget size in the class
record, the widget puts the widget part in the same
field.
⊕ Instead of putting XtVersion in the class record,
the widget puts XtVersionDontCheck in the class
record.
⊕ The widget defines a variable to point to the offset
record. This can be part of the widget's class
record or a separate global variable.
⊕ In class initialization, the widget calls
- 1 -
XmResolvePartOffsets(3Xm) XmResolvePartOffsets(3Xm)
XmResolvePartOffsets, passing it the offset address
and the class record. This does several things:
Adds the superclass (which, by definition, has
already been initialized) size field to the part
size field.
Allocates an array based upon the number of
superclasses.
Fills in the offsets of all the widget 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.
⊕ Instead of accessing fields directly, the widget
must always go through the offset table. You will
probably 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)))
The XmField macro helps you access these fields.
Because the XmPartOffset and XmField macros
concatenate things together, you must ensure there
is no space before or after the part argument. For
example, the following do not work because of the
space before or after the part (Label) argument:
XmField(w, offset, Label, text, char *)
XmPartOffset( Label, text).
Therefore, you must not have any spaces before or
after the part (Label) argument, as illustrated
here:
XmField(w, offset,Label, text, char *)
The parameters for XmResolvePartOffsets are defined
below:
widget_class
Specifies the widget class pointer for the
- 2 -
XmResolvePartOffsets(3Xm) XmResolvePartOffsets(3Xm)
created widget.
offset Specifies the offset record.
- 3 -