In Ashley’s article this morning, she mentioned one of my favorite programs for Vista called Switcher. It makes use of Vista’s advanced graphical capabilities, particularly the Desktop Window Manager (DWM) to provide features that can’t be found in Windows XP. So why is it that they can’t be found in XP?

In versions of Windows prior to Vista, each program window is re-rendered (often referred to as repainting) every time you move it around the screen. If you put one window on top of another it will only render what is visible on the screen at that time. As soon as you start to move the top window, the operating system will begin rendering the underlying window once again, which can cause an effect that many of you are all too familiar with:

Windows XP Repainting
Image from Greg Schechter’s MSDN Blog

In Vista, this is all different with DWM. Every window gets its own buffer that it can paint to, and they are organized in a fashion similar to layers in Photoshop. You can then move a window and it won’t have to re-render all of the windows located behind it, instead it just displays what is already in the buffers.

Because of this, applications like Switcher can easily resize and manipulate windows in almost any way they want without a noticeable performance increase, and best of all is that the thumbnails can provide a live preview of what is actually going on inside the application! Programs for Windows XP that have similar features only take a screenshot of the application and do not show a live preview.

One last thing that I did want to mention was that sometimes in Vista, a preview isn’t available for an application, and all you’ll see is an icon like this:


This typically only happens after a certain period of minimizing the program. There isn’t much of a reason for Windows to constantly have the application rendering, so after not being used for awhile it will replace the live preview with the program’s icon. If you want to restore the preview just maximize the window.

Hopefully that clears up how the Desktop Window Manager in Vista works, and also why it is beneficial. This is just another one of those underlying features in Vista that many people overlook because they don’t fully understand the benefits, but there are some applications that are already starting to take advantage of it.