Windows Desktop Background Rotator

A PowerShell 2.0+ script that sets the desktop background to a randomly chosen image out of a pool of images. Optionally, you can use different pools of images, dependent on the date (useful for having Christmas desktop backgrounds appear only in December, for example). A pool will go through each of its images one time and then start over. Pool usage history is saved in an XML file in the same folder as this script. Intended to be run as a scheduled task.

Instructions

1. Download the script

2. If your desktop backgrounds are stored in a folder named "Desktop Backgrounds" within your "Pictures" folder, you can go to the next step. Otherwise, you will need to open the script in an editor and modify the path used in the Get-Default-Pool function to point to the correct location.

3. If you only want to pull from one pool of images regardless of the date, you can go to the next step. Otherwise, follow the steps in the "Using Different Pools of Images Depending on the Date" section below before going to the next step.

4. If you want your desktop backgrounds' fit / position to be "Stretch", you can go to the next step. Otherwise, you will need to open the script in an editor and modify the last line of code. Specifically, the second parameter passed to [Wallpaper.Setter]::SetWallpaper. 0 is "Tile", 1 is "Center", 2 is "Stretch", and 3 is "NoChange".

5. If you want this script to be run automatically on a schedule, set up a scheduled task to do so.

Using Different Pools of Images Depending on the Date

There are three steps to setting up an additional pool of images to pull from during a specific date range:

1. Define a function

2. Add an entry to the $Dates array

3. If necessary, update the Get-Default-Pool function to exclude the images that should only be in this additional pool

The following example assumes this file structure:

...
└── Pictures
    └── Desktop Backgrounds
        ├── Holidays
        │   ├── Christmas
        │   │   ├── christmas_desktop_background1.jpg
        │   │   ├── christmas_desktop_background2.jpg
        │   │   └── christmas_desktop_background3.jpg
        │   └── Thanksgiving
        │       ├── thanksgiving_desktop_background1.jpg
        │       ├── thanksgiving_desktop_background2.jpg
        │       └── thanksgiving_desktop_background3.jpg
        ├── regular_desktop_background1.jpg
        ├── regular_desktop_background2.jpg
        └── regular_desktop_background3.jpg

Example Part 1: Christmas

Suppose you wanted Christmas desktop backgrounds to be used from December 1st through December 25th each year. You would first define a function such as Get-Christmas-Pool:

Function Get-Christmas-Pool {
	Get-ChildItem "$([Environment]::GetFolderPath(`"MyPictures`"))\Desktop Backgrounds\Holidays\Christmas"
}

Next, you would add an entry to the $Dates array, like this:

$Dates = @(
	@{
		"StartDate" = "12-01"
		"EndDate" = "12-25"
		"Pool" = "Christmas"
	}
)

Note that whatever you set Pool to must match the function name. Since our function is named Get-Christmas-Pool, we set Pool to Christmas.

Finally, because of the file structure of our desktop backgrounds, we will need to update the Get-Default-Pool function to exclude the holiday desktop backgrounds, like this:

Function Get-Default-Pool {
	Get-ChildItem "$([Environment]::GetFolderPath(`"MyPictures`"))\Desktop Backgrounds" -Recurse | Where-Object {! $_.PSIsContainer -And $_.FullName -NotMatch "Holidays"}
}

Example Part 2: Thanksgiving

Now suppose you wanted Thanksgiving desktop backgrounds to be used on Thanksgiving Day each year. You would first define a function such as Get-Thanksgiving-Pool:

Function Get-Thanksgiving-Pool {
	Get-ChildItem "$([Environment]::GetFolderPath(`"MyPictures`"))\Desktop Backgrounds\Holidays\Thanksgiving"
}

Next, you would add an entry to the $Dates array. But this time, it will need to be done differently since the date of Thanksgiving Day varies from year to year. Here is an example of what you might do:

$Dates = @(
	...
)

$Today = (Get-Date)

If ($Today.Month -Eq 11 -And $Today.Day -Ge 22 -And $Today.Day -Le 28) {
	$DayOfWeekOnFirst = [Int]([DateTime]"$($Today.Year)-11-01").DayOfWeek
	$FourthThursdayDate = 22 + (11 - $DayOfWeekOnFirst) % 7
	$Dates += @{
		"StartDate" = "11-$FourthThursdayDate"
		"EndDate" = "11-$FourthThursdayDate"
		"Pool" = "Thanksgiving"
	}
}

Since the Get-Default-Pool function is already set up to exclude our holiday desktop backgrounds, we are done.