The window manager expects to find two XPM files for each icon specified in the configuration files as ICON. They should be named like this:
_16x16.xpm
A small 16x16 pixmap.
_32x32.xpm
A normal 32x32 pixmap.
_48x48.xpm
A large 48x48 pixmap.
Other pixmap sizes like 20x20, 24x24, 40x40, 48x48, 64x64 might be used in the future. Perhaps we need a file format that can contain more than one image (with different sizes and color depths) like Windows'95 and OS/2 .ICO files.
It would be nice to have a feature from OS/2 that varies the icon size with screen resolution (16x16 and 32x32 icons are quite small on 4000x4000 screens ;-)