|Tip 203||Hack Dashboard/Mission Control Backgrounds|
The wallpaper backgrounds that you see behind Dashboard and Mission Control can easily be replaced. They’re actually patterned wallpaper tiles rather than large images, and they’re repeated from left to right and from top to bottom along the screen. To replace them, you’ll need to source a similar small pattern image that’s designed to be repeated when used as desktop wallpaper, or you can choose image files that are the same size as your monitor resolution (beware: if an image is too small, OS X will repeat it, creating an ugly effect). You’ll find many wallpaper pattern images by searching using Google.
Sadly, because of the way they handle wallpapers, this isn’t a trick that will work with MacBook Pro computers with Retina displays.
The following steps modify system files, and this tip therefore affects all users of the computer. Ensure you have an up-to-date Time Machine backup. Like all tips that involve hacking system files, you might find your changes reverted to the default settings if you install a major operating system update. The solution is simply to repeat the steps.
Replacing the Main Wallpaper Images
Here are the steps for replacing the wallpapers:
Once you’ve found your designs, you’ll have to convert them to PNG images, if they aren’t already. To do so, open them in Preview by double-clicking them, and then click File→Export. Choose PNG from the Format drop-down list. Finally, click Save.
Rename the file you intend to use to replace the Mission Control wallpaper as defaultdesktop.png. Rename the file you intend to use for the Dashboard wallpaper as pirelli.png.
Open Finder and hit Shift+Command+G, typing the following in the dialog box that appears: /System/Library/CoreServices/.
Look for the Dock file. Right-click it and select Show Package Contents from the menu that appears.
In the new Finder window, browse to the Contents folder and then the Resources folder. Then locate the existing defaultdesktop.png and pirelli.png files in the folder, and drag them to a backup location on your hard disk (for example, your Documents folder). Keep these backups safe!
Now drag and drop your new defaultdesktop.png and pirelli.png files on top of the Finder window that is browsing the Resources folder.
Click the Authenticate button in the warning dialog box that appears, and then click the Replace button in the dialog box that warns about files already existing in the location. Type your password when prompted.
That’s it! Log out and back in again for the changes to take effect.
Replacing the Dashboard Thumbnail Image
The only negative to this tip is that the thumbnail preview of Dashboard within Mission Control still uses the old Dashboard background. The image used for this miniature background is called mini_pirelli.png, and it’s located in the same folder within the Dock package, like the images mentioned earlier.
The mini_pirelli.png thumbnail of the Dashboard is always 10 percent of your screen’s resolution—on my MacBook’s 1280 x 800 screen, the thumbnail is 128 x 80 pixels, for example, while on my 1920 x 1080 external monitor, the thumbnail is 192 x 108. This makes creating a replacement background for the Dashboard thumbnail easy—simply create a copy of the pirelli.png image you used earlier and reduce it to 10 percent. To do this in Preview, open the image, click Tools→Adjust Size, and change the Pixels drop-down in the dialog box to read Percent. Then enter 10 in the Width and Height fields and click OK. Then click File→Export and save the image as mini_pirelli.png. Replace the default version of the file within the Dock package, as described previously, backing up the original first.
Log out and back in again for the changes to take effect.
Restoring the Default Wallpapers
To restore the default wallpapers later, open a Finder window, hit Shift+Command+G, and type /System/Library/CoreServices/. Once again, right-click the Dock file, and select Show Package Contents, browsing to the Resources folder. Then locate the backups you made of the original two (or three) files and drag and drop them onto this Finder window. Again, you’ll need to click the Authenticate button and the Replace button in the dialog boxes that appear. Type your password when prompted, and then log out and back in again for the changes to take effect.