XmResolveAllPartOffsets(3X) UNIX System V 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, (caddr_t)False } };
XmPartResource constraints[] = {
{ BarNmaxWidth, BarNMaxWidth,
XmRDimension, sizeof(Dimension),
XmConstraintPartOffset(Bar,max_width),
XmRImmediate, (caddr_t)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.
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XmResolveAllPartOffsets(3X) UNIX System V XmResolveAllPartOffsets(3X)
⊕ 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).
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XmResolveAllPartOffsets(3X) UNIX System V XmResolveAllPartOffsets(3X)
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.
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