The Xlib library is the basic layer of the X11 windows system. It contains functions to perform all primitive operations on the display, keyboard and other I/O units: open a window, display lines, polygons, text, move the cursor, etc. etc. These functions are very primitive and therefore very fast. For some applications this kind of output is sufficient and even necessary, namely when only a simple output is required, and it must be very fast, or if large data quantities have to be displayed.
ProTcXl gives the user a simple interface to Xlib calls which are executed on Tk windows. It is not a full and stand-alone Xlib interface, like e.g. XWIP, first because Xlib alone is not sufficient for most applications, and second because using Xlib alone is quite difficult and tedious. The idea of the interface is the following: