XmResolveAllPartOffsets(3X) SDK X11 R4.11MU05 XmResolveAllPartOffsets(3X)
NAME
XmResolveAllPartOffsets--A function that allows writing of upward-
compatible applications and widgets
SYNOPSIS
#include <Xm/XmP.h>
void XmResolveAllPartOffsets (widgetclass, offset, constraintoffset)
WidgetClasswidgetclass;
XmOffsetPtr* offset;
XmOffsetPtr* constraintoffset;
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,maxwidth),
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
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.
#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 maxwidth:
#define BarMaxWidth(w) \
XmConstraintField(w,constraintoffsets,Bar,maxwidth,Dimension)
The parameters for XmResolveAllPartOffsets are defined below:
widgetclass
Specifies the widget class pointer for the created widget
offset Returns the offset record
constraintoffset
Returns the constraint offset record
RELATED INFORMATION
XmResolvePartOffsets(3X).
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