XmResolveAllPartOffsets - Man Page

#include <Xm/Xm​.h>
void XmResolveAllPartOffsets(
WidgetClass widget_class,
XmOffsetPtr * offset,
XmOffsetPtr * constraint_offset);

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 steps described in the following paragraphs​.

Instead of creating a resource list, the widget creates an offset resource list​. To 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 structure 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 } };

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 that 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, 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

widget_class

Specifies the widget class pointer for the created widget

offset

Returns the offset record

constraint_offset

Returns the constraint offset record

XmResolvePartOffsets(3)​.

XmResolvePartOffsets(3).