// uses mode "fit to screen"
static void wallpaper(S imageID) {
  print("Setting wallpaper to: " + imageID);
  
  if (isLinux()) {
    File img = loadImageAsFile(imageID);
    S cmd = "pcmanfm " + bashQuote("--set-wallpaper=" + img)
      + " --wallpaper-mode=fit";
    print(backtick(cmd));
    print("Wallpaper set to " + imageID + ", hopefully.");
  } else if (isWindows()) {
    File img = prepareProgramFile("#1004273", parseSnippetID(imageID) + ".bmp");
    saveBMP(loadImage2(imageID), img);
    assertTrue(img.getAbsolutePath(), img.isFile());
    
    S cmd = "reg add \"HKEY_CURRENT_USER\\Control Panel\\Desktop\" /v Wallpaper /t REG_SZ /d " + bashQuote(img) + " /f";
    backtick(cmd);
    
    // Set to "fit" (WallpaperStyle=6, TileWallpaper=0) doesn't seem to work
    // So set to "center"
    cmd = "reg add \"HKEY_CURRENT_USER\\Control Panel\\Desktop\" /v WallpaperStyle /t REG_SZ /d " + 0 + " /f";
    backtick(cmd);
    cmd = "reg add \"HKEY_CURRENT_USER\\Control Panel\\Desktop\" /v TileWallpaper /t REG_SZ /d " + 0 + " /f";
    backtick(cmd);
  
    cmd = "RUNDLL32.EXE user32.dll, UpdatePerUserSystemParameters";
    backtick(cmd);
  } else
    fail("Don't know how to set wallpaper for your OS");
    
  print("Wallpaper set (hopefully)!");
}