Desktop Background

Friday, August 14, 2015

One of the benefits of learning to program is learning how to automate tasks performed with a computer. I thought it might be fun to build a simple vocabulary to allow getting and setting of the desktop background picture. Since Factor makes it pretty easy to build cross-platform vocabularies, we will implement this on Mac OS, Linux, and Windows.

Our API consists of two words, one that gets the current desktop picture and one that sets a new desktop picture, dispatching based on which operating system we are running on (technically, based on the value of the os variable).

HOOK: get-desktop-picture os ( -- path )

HOOK: set-desktop-picture os ( path -- )

Mac OS

On Mac OS, we use AppleScript to ask the Finder what the path to the current desktop picture is, or tell it to set the desktop picture to a specific path.

M: macosx get-desktop-picture
    {
        "osascript" "-e"
        "tell app \"Finder\" to get posix path of (get desktop picture as alias)"
    } utf8 [ readln ] with-process-reader ;

M: macosx set-desktop-picture
    absolute-path
    "tell application \"Finder\" to set desktop picture to POSIX file \"%s\""
    sprintf run-apple-script ;

Windows

On Windows, we use the SystemParametersInfo function to get and set the desktop wallpaper.

CONSTANT: SPI_GETDESKWALLPAPER 0x0073

CONSTANT: SPI_SETDESKWALLPAPER 0x0014

M: windows get-desktop-picture
    SPI_GETDESKWALLPAPER MAX_PATH dup 1 + WCHAR <c-array> [
        0 SystemParametersInfo win32-error<>0
    ] keep alien>native-string ;

M: windows set-desktop-picture
    [ SPI_SETDESKWALLPAPER 0 ] dip utf16n encode
    0 SystemParametersInfo win32-error<>0 ;

Linux

On Linux, which has many different desktops, we are going to assume a GNOME environment. Other window managers have different ways to change the desktop background.

M: linux get-desktop-picture
    {
        "gsettings"
        "get"
        "org.gnome.desktop.background"
        "picture-uri"
    } utf8 [ readln ] with-process-reader
    "'file://" ?head drop "'" ?tail drop ;

M: linux set-desktop-picture
    {
        "gsettings"
        "set"
        "org.gnome.desktop.background"
        "picture-uri"
    } swap absolute-path "file://" prepend suffix try-process ;

This is available on my GitHub.