17.2.1 Shell Positions
You can position a shell at a specific location on the screen using the XmNx and XmNy resources. In addition, you can
set the XmNx and XmNy resources of the immediate child of a shell widget to position the shell. This feature exists
because Motif dialogs are designed to make their shell widgets invisible to the programmer. It is typically easier to set
these resources directly on the child of a shell, as you are more likely to have a handle to that widget. The following
code fragment shows how you can position a MessageDialog in the center of the screen:
Widget dialog, parent;
Dimension width, height;
Screen screen = XtScreen (parent);
Position x, y;
dialog = XmCreateMessageDialog (parent, "dialog", NULL, 0);
/* get width and height of dialog */
XtVaGetValues (dialog,
XmNwidth, &width,
XmNheight, &height,
NULL);
/* center the dialog on the screen */
x = (WidthOfScreen (screen) / 2) − (width / 2);
y = (HeightOfScreen (screen) / 2) − (height / 2);
XtVaSetValues (dialog,
XmNx, x,
XmNy, y,
NULL);
You can position a dialog in this way because the Motif BulletinBoard widget passes positional information to its
shell parent. See Chapter 5, Introduction to Dialogs, and Chapter 7, Custom Dialogs, for further discussion. In most
cases, you shouldn't be setting the XmNx and XmNy resources for a dialog because it is the job of the window manager
to position shells. The user can also have some say in how placement should be handled. For example, if the user has
set the interactivePlacement ...