When X Doesn t Cut It

When X Doesn't Cut It

I'm a consultant. Please don't hold that against me. This simple fact means that I move around a lot. I move from place to place many times each year. In each place, I am forced to use different hardware, software, networks, and so forth.

You already know, because you are reading this book, that I use Linux. I use Linux a lot. I tend to use Linux to develop software for every environment, including Windows , because I like the tools Linux gives me.

I recently had occasion to work in an environment that I would consider quite atypical. A client was using OS/2 to build and deploy a 16-bit Powerbuilder application that connected over a token-ring network to a middle tier implemented using CICS on AIX! Over time, I managed to get a PC reassigned to running RedHat for a variety of internal documentation (another adventure, recounted in Chapter 9 ). Now I had continuous access to my favorite tools. OS/2 even has an X-server, called PMX, so I could run applications on the Linux box and display them on my desktop ”almost.

What Is a Window Manager?

X-windows is a system that divides the labor up quite a bit. An X-windows application draws and controls only the area "inside" the window, the so-called client area. A totally separate program, called a " window manager " paints the borders and controls (such as resizing edges, maximize, minimize, and close buttons ). You can have only one window manager program per X server, and that window manager provides these window "decorations" on behalf of all windows.

The window manager and the X-application communicate in standard ways. For example, when you resize a window by dragging an edge, all the work is done by the window manager program until you release the edge; then the window manager tells the X application about it by sending it a resize message. The application then must repaint itself in the new client area. (This is a bit theoretical: Some window managers send repaint messages while you drag the edge, so the application repaints several times, but you get the idea.) The application is also able to tell the window manager certain things, such as whether or not the window may be resized.

The division of labor has some distinct advantages, especially when you consider X's network capabilities. If the window manager is local, then when, for example, resizing the window of a remote application, only the final "window resize" and screen repaint need go over the network. None of the mouse events or border animation need to generate network traffic. (Again, if your window manager sends repaint messages as it goes, this benefit is lost.)

The other advantage is that you can change window managers. You might have an industrial application that is always maximized and should not be closed. You could write a window manager that doesn't have a close button or resizing decorations and that always sets the client area size to the full screen. Heck, some existing window managers can be configured to do this without any programming.

The details of window managers and their interaction with applications can get quite complex. There is a sort of "minimum standard" set of features a window manager must provide, and there is a "minimum standard" set of window manager messages an X-application must support, but many applications go well beyond this. The increasingly common "desktop" systems for X (KDE and GNOME, for example) extend this set quite, er, extensively. This means that applications that use these features either will run only with that one window manager or will have some functionality unavailable when running under other window managers.

If you want to know more, it is time for you to delve into X-windows programming.

VNC is available from the URLs noted at the beginning of the chapter. As for X-servers for Windows, a number of commercial ones are available. Since this book is about Free Software, however, we will not lead you to those.

A free X-server for Windows is available as part of a product called Cygwin, which is a complete POSIX-compliant programming environment for Windows. Cygwin actually makes Windows itself into a decent Unix-like environment. The X-server for Cygwin is the same X-server shipped with most Linux distributions: Xfree86.

Cygwin is available from Cygnus Software, which was purchased by RedHat last year. The URL is http://sources.redhat.com/cygwin .

I found that a great many "normal" applications, such as Wine (see Chapter 17 ) and the GIMP (see Chapter 22 ) would crash the OS/2 PMX server. Not only that, but the OS/2 PMX server insists on using OS/2 Presentation Manager as the window manager. (If you do not know what this means, see the " Window Manager " sidebar.) I found myself with a classic problem: How, if Linux is not my primary system, do I get a decent X-server?

This problem exists for Windows users as well. There are a couple of free X-servers out there for Windows, but they are quite limited in capability. There are some excellent commercial X-servers for Windows, but if you are like me, your software budget is limited (nonetheless, we will list URLs for a few of the commercial ones as well).

I began looking for alternatives. I was already familiar with something called VNC, which stands for "virtual network console" and is similar to PC-Anywhere. It basically allows you to access another machine's console as if you were sitting at that machine. To understand the differences, we will have to review the design of X and of VNC ( Figure 2-1 ).

Figure 2-1. Block diagram of an X-windows environment.