Multiple Screens: A Usability Nightmare?

I’m surprised I haven’t seen anything about this anywhere else. When multiple screens are connected together, you lose one (or two) of the most important features of a single window: the right and left edges. As Bruce Tognazzini mentions in his timeless article on Fitts’ Law, the edges are very fast for user access. This is one reason that Apple’s menu bar (across the top) is so much better than the way Sun and Microsoft and others have done it: see point 5 in Tog’s article.

There is also an absolutely wonderful writeup of Fitt’s Law by Kevin Hale titled Visualizing Fitts’ Law – with a presentation with excellent visualizations and examples. Jensen Harris also wrote an article on Fitts’ Law: of particular note are the examples of how Fitts’ Law affected the design of Microsoft Windows and Microsoft Office.

In Tog’s article on Fitts’ Law, he describes how he experimented with “multiple desktops” (though at the time, it may have seemed more arbitrary than that). With a second monitor on top of the first, and a menu that users could “bypass” into the top monitor, it actually slowed the user down quite considerably: at first, the menu was missed quite often until the user slowed way down to get at the menu.

When using multiple monitors in a horizontal direction (a typical layout) the right edge of the left screen and the left edge of the right screen become very hard to hit. This especially becomes a problem with programs that are maximized. Consider the example of a typical scrollbar (normally on the right hand side) on a maximized application on one of the two monitors. On the left-side monitor, it becomes a hard target as the user has to directly aim and slow down to hit it. If on the right-side monitor, the scroll bar essentially becomes infinitely large and can be hit without any trouble at all.

Using multiple monitors also completely eradicates two of the five easiest locations to reach: two corners are no longer easily “reachable” – or perhaps reachable at all. This easy reachability of the corner is perhaps one reason that programs put the window control buttons in the top right corner; with another monitor on the right the corner becomes that much harder to hit. If there is a monitor above, then it becomes just that much harder.

When using multiple monitors on on system tied together, the possibilities of rectifying this usability problem is only available to the extent that the operating system allows it. However, if you use synergy to tie multiple computer displays together, there is at least, several ways to regain the “infinitely large” target of a screen edge.

One is to use the “lockCursorToScreen” capability of Synergy. Synergy uses the ScrollLock key to do this by default. You can also use a hot key – this display is from the Synergy+ server for Windows:

Hot Key Configuration Window
Hot Key Configuration Window

Hot Keys are set at startup, accessable via the Hot Keys button. With a mouse and window “locked” with this option, you get back your right and left edges, and they once again behave the way operating system designers expected. With the toggle, you can go back and forth. There is, however, no way to discern whether the screen is locked or not, aside from the fact that the ScrollLock key setting is often visible on the keyboard: this is a usability failing in this feature.

Using the “double-tap” or “time delay” features of Synergy (with respect to switching displays) turns out to be extremely frustrating for the user, switching at times that are unexpected and not switching when desired.

Another possibility would be to not link the multiple displays together at all, and use key commands to switch between screens. This, however, may be more trouble than it is worth; I’ve not tried it and it does not seem possible to configure Synergy+ this way from the configuration screens.

Using synergy: Trips and Traps

Synergy is a program to combine a number of host displays together (using one keyboard and mouse). Using the network, it allows you to move your mouse seamlessly from one system’s display to another – including combining many displays in this way. However, there are some trips for the unwary – or just plain surprises. None of this should make you stop using synergy; but knowing about it and what to do about it can make your use of synergy better. If you aren’t already using synergy, you should be.

The network data used by synergy is unencrypted. This means when you type in passwords on a synergy client, the passwords are sent in the clear across the network. To take care of this, use an ssh tunnel:

$ ssh -R 24800:syn-server:24800 syn-client

Then on the synergy client host, use for the synergy server address:

$ synergyc

This will encrypt the traffic between the two hosts.

If any process hogs the processor on the machine your mouse is active on, you won’t be able to switch to another display. This makes sense when you think about it, but it still can come as a surprise. What is happening is that the synergy client program is not able to run, so it doesn’t respond when you hit the edge of the screen. Still, it would be nice if the server would recognize a client in this state and relocate the mouse somewhere you can use it.

The mouse can spontaneously relocate. This can happen for a variety of reasons – the most common is that while the synergy “mouse” has a different location than the actual mouse. When you switch from one to the other, the operating system thinks the mouse has “jumped” and moves the mouse pointer on screen accordingly. On inactive systems (where synergy does not have a pointer) the “physical” mouse pointer is usually put at the center of the screen (and usually hidden). Again, this is a little bit of a surprise, but not damaging.

The Windows-based synergy server may stop handling remote clipboards. This has been a bug with the Windows version of synergy, and can be “fixed” be restarting synergy.

XWindows clipboards may appear to not transfer. This is because XWindows has two clipboards. When you select a string of text in an xterm, for example, the data is put into a particular clipboard. However, this is not the primary clipboard and thus synergy does not transfer it. You can copy the selected text with a right-click menu and selecting “Copy…” or you can use a program like xclip to move the clipboard data into the right place.

With all of those desktops together, you’ll find that you may lose the location of the mouse from time to time. This is where the capability of “locating” the mouse with the press of a key comes in handy. Windows will do this, as will GNOME and KDE. Windows is configured to answer to a single press of the Control key. Some systems show you where the mouse is with a ever-shrinking set of rings (Windows) or squares (Fedora); Linux Mint is set up to flash a disk around the cursor.

When moving the mouse cursor across all of the different desktops, the speed and acceleration of each controls how the mouse moves when it is in that desktop. This can present itself in the form of a desktop acting like “quicksand” – the mouse moves fast until it gets to a desktop, then on that desktop the mouse moves slower until it gets to the other side. Adjust the mouse properties of each system until the mouse acts appropriately. You still won’t be able to (probably) shove the mose over and have the mouse go all the way from right to left (or vice versa) but moving will be nicer.

Watch where your mouse focus is. When you select a text box on one system, you typically then may move the mouse “out of the way.” However, if “out of the way” means the mouse is now on another system, then when you type the characters will go somewhere you don’t want them to go. This can be dangerous if you are typing in a password; don’t let your password go out over IRC or something because the wrong system’s desktop is active. It may be a good idea to break off the habit of moving the mouse off to the side; you don’t need to do this.