Dual monitors have been around for a long time, yet still Microsoft hasn't included support for a single wallpaper to span all monitors. You can however use dual-monitor wallpapers in Windows with a little bit of fiddling.
Provided you have your left-most monitor as the primary monitor for your system, then all is well, find your dual-monitor wallpaper, set it in display properties, but make sure the image is set to tiled. You can edit the image so that it better matches your combined resolution.
If your left-most monitor isn't your primary monitor, don't despair, there is another even more fiddly solution. Read on.
You can calculate your combined resolution by adding up the resolutions of each monitor's axis where they join. For example, if you have two monitors at 1280x1024 side by side, your combined resolution will be 2560x1024, if you have them vertical, then your combined resolution would be 1280x2048.
The problem with dual-monitor wallpapers and Windows gets even more messy when the primary display isn't at the left. To put this simply, Windows (when tiled) will always draw the desktop wallpaper starting at the top left of the primary monitor. It will then flow onto the secondary monitors from left to right. Once it reaches the end of the monitor row, it will then go back to the start: any secondary monitors before your primary monitor.
This sounds complicated, and when things get complicated, diagrams help. Here is an example setup:
Using an image similar to that above as the wallpaper shows the problem. As said, Windows will draw the wallpaper from the top left of the primary display, and then wrap around onto the secondary display causing the image to break up:
In order to get the image to display properly, you need to edit it so that it wraps correctly. The rest of this article will explain how to do just that.
Until Microsoft decide to support dual-monitor wallpapers properly, you have a few choices. They are:
For this tutorial, I'll be using the wallpaper shown below, you can find the original here. When finding an image to use, try to make sure it's dimensions are at least equivalent to your combined resolution, or as close as you can find. This is one of those areas that is really good at confusing people, including myself, so I'll try keep this simple.
To follow this tutorial, you will need an image editing application that supports layers, such as Adobe Photoshop, the GIMP or Adobe (Macromedia) Fireworks. It is still possible to do this without layers, but they make it a lot simpler.
You should end up with an image that looks like that shown below, the diagram shows how the image fits together when drawn by Windows.
It's as simple as that :-)
I will when I have time, write a small application to make this automated. But not today.
6th Jan 2009 - Update: As promised, you can download the Dual-Monitor Wallpaper Tweaker from here.