Plug-Ins

A ``plug-in'' is a software library that is read into a running program, that provides additional features or capability. Within Xic, plug-ins provide optional support for OpenAccess, and the Python and Tck/Tk languages. The plug-in provides an interface to external libraries that may or not be present on the user's computer. If the needed libraries are present, the plug-in will be loaded into Xic on program startup, and a message, such as

``Using Tcl/Tk (tcltk.so)''

will appear in the console among the text generated on program startup. If the needed libraries are not found, the plug-in is not loaded, but Xic will run normally except that the plug-in's features will be absent.

At present, plug-ins are supported on all platforms except for Microsoft Windows. Windows does not provide the type of shared library technology needed for plug-ins. Although a similar capability could be instituted, there are many substantial issues and it is not clear if it is worth the development effort.

Plug-ins are distributed as shared library code, and are found in the plugins sub-directory in the distribution area, i.e.,

prefix/xictools/xic/plugins

The plug-in files are version-specific, and will work only with the program from the same distribution file. Of course, Xic needs to be able to find its startup files for the plug-ins to be available. If Xic is not installed in the standard location, the XT_PREFIX environment variable should be set to enable Xic to find its startup files.

Normally, if a plug-in is not loaded, there is no message. If, however, the XIC_PLUGIN_DBG environment variable is set, diagnostic messages will be printed. These can help identify why the plug-in is not being loaded, and are instrumental in tracking down problems when the user expects success.

Lack of success loading a plug-in and generally due to the inability of the plug-in code to find the shared libraries needed on the host computer. Unless the library is ``standard'' on the system, which may be true of Python, then it will be necessary to use the LD_LIBRARY_PATH environment variable to specify where to look for the libraries. The libraries much match the address size (32 or 64 bit) of the running Xic program.