Mastering Perl/Tk

Some Perl/Tk History

Perl/Tk has its roots in the X Window System and the Tcl language. So let’s take a detour into the pages of history, to give you an idea of where Perl/Tk came from and how it got here.

The X Window System and Xlib

The X Window System (known to its friends as just “X” or “X11”) was first released in 1987 as a graphical platform for Unix systems. Like most Unix software, X applications are almost universally written in the C language, using a library such as Xt, Motif, or (if you were really unlucky or just really brave) the underlying library for X-based applications, Xlib.

Xlib has the advantage that you can do anything, at the expense of dealing with everything. For instance, here’s one way to make a simple pull-down menu using Xlib (which is one statement in Tk). First, determine the dimensions of the longest menu item. For argument’s sake, assume the menu label string is in the C variable menu_item. Subroutine XTextExtents determines several metrics about menu_item, such as its overall width in pixels in the current font and its pixel height, computed by summing the maximum ascent and descent (the number of pixels above and below the baseline, respectively). After accounting for the number of menu items, border widths, and including some slop for good luck, we arrive at the dimensions of the menu window itself, and its relative (x, y) position in the MainWindow.

 XTextExtents( font_info, menu_item, strlen( menu_item ), &direction, &ascent, &descent, &overall ...