Web, Graphics & Perl/Tk Programming

Chapter 36. The Mouse Odometer

Steve Lidie

If you read Getting Started with Perl/Tk and Scoreboard: A 15-Minute Perl/Tk Application, you should be a seasoned Tk novice by now. Assuming so, let’s move right along and examine the Perl/Tk implementation of the Mouse Odometer, named modo and pictured in Figure 36-1.

Figure 36-1. modo, the mouse odometer

modo has got to be one of the most pointless programs ever written. But it illustrates numerous Perl/Tk features, so it does have some value. I first saw similar code for the Mac, written by Sean P. Nolan, that simply tracked a machine’s cursor. Currently I have logged well over 51 kilometers on my cursor, and my mouse has careened around its pad some 14 kilometers.

Measuring Distance

Most of this column is not about modo and how it works, but rather the Perl/Tk features it uses. This time we’ll learn how to schedule asynchronous timer events, and look more closely at window manager commands, menus, menubuttons, and the ColorEditor. We’ll also create and explain in detail an object-oriented Perl/Tk composite widget that we’ll create called the Odometer. Like a car’s odometer, we want our mouse odometer to record the physical distance traveled by the mouse, not the number of pixels. In a car, you want to know how many miles you’ve traveled, not merely the number of tire-lengths, which will vary from car to car. In the X window system you can ...