Custom Keymaps

The problem

When using custom keymaps with custom modifier keys, rofi will not be able to use these modifiers.
The following writeup was done by mardukbp.

Relevant bug report: https://github.com/DaveDavenport/rofi/issues/307

xmodmap

In the following I will assume that the current keymap is vanilla us: setxkbmap us -option.

The current keymap can be exported to a file with xmodmap -pke > xmodmaprc. This file contains a dictionary mapping keycodes to keys. If one wants to e.g. use Alt_L as Shift_L, it is only a matter of changing the line corresponding to keycode 64 and then calling xmodmap xmodmaprc.

Now issuing xmodmap shows that no keycode is bound to Alt_L and rofi will obviously complain. How does one make rofi happy? Add the following lines at the BOTTOM of xmodmaprc:

clear mod1
add mod1 = Alt_L Alt_R Meta_L

Adding lines beginning with clear and add at the top of the file when a lot of keys have been remapped leads to anger->hate->suffering (that's what happened to me!).

Now running xmodmap xmodmaprc && xmodmap will show that there is an Alt_L bound to keycode 204 (0xcc), that is Alt_R + Alt_L = Alt_L, and rofi will not complain anymore. However, xmodmap will only report two Shift keys when in reality there are now three. Adding the following lines to the bottom of xmodmaprc takes care of this:

clear shift
add shift = Shift_L Shift_R

Bottom line

Whenever one rebinds the keycodes of modifier keys in xmodmaprc one also has to update the modifier map. This is done using the commands clear and add as explained above.