Mastering Perl/Tk

Using the Option Database

The option database is populated by several mechanisms. We already know Tk::CmdLine::SetArguments sets standard X11 options prior to MainWindow creation. Unix users should be familiar with the .Xdefaults file, a simple text file that can contain resource entries and is one of the files Tk::CmdLine::SetArguments reads during MainWindow initialization. Perl/Tk programs can load resources from other files as well by calling Tk::CmdLine::LoadResources or optionReadfile . Or, Tk::CmdLine::SetResources and optionAdd can add individual resources to the option database. For the location of other resources files, please read the manpage for Tk::CmdLine.

Here are some sample resource entries:

*font                         : 12x24
frog*Foreground               : blue
frog.button1.Background       : orange
frog.b3.foreground            : green
frog*Label*cursor             : gobbler

Note that the resource pattern is to the left of the colon, and its value to the right. The pattern can be general (such as the first entry, which changes the default font for every X and Tk application) or specific (such as the fourth entry, which changes only the foreground color of the widget named b3 of the application frog).

A resource pattern identifies an option and one or more widgets in the window hierarchy. Tk generates the hierarchy automatically, assigning string pathnames to each widget. In Chapter 13, we learned that Tcl/Tk programmers are required to do this manually. In Perl/Tk, we seldom need to refer to widget pathnames; ...