XmResolvePartOffsets(3X) OSF XmResolvePartOffsets(3X)
NAME
XmResolvePartOffsets-A function that allows writing of
upward-compatible applications and widgets
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 access to widget instance
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.
XmPartResource resources[] = {
{ BarNxyz, BarCXyz, XmRBoolean,
sizeof(Boolean), XmPartOffset(Bar,xyz),
XmRImmediate, (XtPointer)False }
};
⊕ Instead of putting the widget size in the class record,
the widget puts the widget part size 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, of type XmOffsetPtr, 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 (printed 6/8/92)
XmResolvePartOffsets(3X) OSF XmResolvePartOffsets(3X)
XmResolvePartOffsets, passing it a pointer to contain
the address of the offset record 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
⊕ 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 macro
helps you access these fields. Because the
XmPartOffset and XmField 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)))
The parameters for XmResolvePartOffsets are defined below:
2 (printed 6/8/92)
XmResolvePartOffsets(3X) OSF XmResolvePartOffsets(3X)
widget_class
Specifies the widget class pointer for the created
widget.
offset Returns the offset record.
RELATED INFORMATION
XmResolveAllPartOffsets(3X).
3 (printed 6/8/92)