Log hook which changes the wallpapers depending on visible workspaces.

This module requires imagemagick and feh to be installed, as these are utilized for the required image transformations and the actual setting of the wallpaper.

This was especially tested with multi-head setups - if you have two monitors and swap the workspaces, the wallpapers will be swapped too, scaled accordingly and rotated if necessary (e.g. if you are using your monitor rotated but only have wide wallpapers).

Add a log hook like this:

myWorkspaces = ["1:main","2:misc","3","4"]
...
main = xmonad $ def {
  logHook = wallpaperSetter defWallpaperConf {
                               wallpapers = defWPNames myWorkspaces
                                         <> WallpaperList [("1:main",WallpaperDir "1")]
                            }
  }
...

• implement a kind of image cache like in wallpaperd to remove or at least reduce the lag
• find out how to merge multiple images from stdin to one (-> for caching all pictures in memory)