The X Public Access (XPA) Mechanism

The X Public Access (XPA) mechanism is the heart of SAOtng. XPA allows an Xt program to define named public access points through which data and commands can be exchanged with external programs. The following short papers give an overview of the XPA and its use in SAOtng:

Public Access Programming: Opening The Black Box That Hides Internal Data (from the 1993 ADASS Software conference)
Applying Public Access Programming Techniques To SAOimage" (from the 1994 ADASS Software conference)

Another view of XPA can be found in the article entitled "The X Public Access Mechanism" (Mandel, Swick, Tody), published in The X Resource, issue 13.

Nearly all of SAOtng's menu functions also are defined to be XPA public access points. As a result, SAOtng can be controlled directly through its menu-based GUI or externally through the xpaset and xpaget programs. For example, the scaling algorithm can be changed and the current scale value is queried:

    csh> xpaget SAOtng scale
    linear
    csh> echo "scale log" | xpaset SAOtng
    csh> xpaget SAOtng scale
    log

The imset and imget programs are provided as a convenience. These programs assume that the target is SAOtng and allow a more natural command structure:

    csh> imget scale
    linear
    csh> imset scale log
    csh> imget scale
    log

The X Public Access (XPA) Mechanism

Last Updated June 14, 1997