When one modifier key is released, only the same key is drawn, even if
there are other identical modifier keys. Be consistent with this
optimization, and only draw the exact key that was pressed when a
modifier key is pressed.
Most future modifier keys will be accents that wouldn't be represented
with an actual key press. Only emit modifier keys as key presses if they
are of the other type (Ctrl, Alt, Shift).
Keys are unsupported if they have no name, or if xkeysym uses a
different format for their name (e.g. XF86Fn). Skip key symbols that
have no name and can't be added to the text keymap.
To support this, set the availability of each keysym before updating the
keymap.
If the key value can emit text, it should put the text to be emitted in
the text field. It should not put any special symbol for the key label,
and it should instead be a special case in the display_label() method.
Some keys may have no XKB key symbol, but still have the ability to emit
text. Examples include the "‹" (U+2039) and "›" (U+203A) characters. Add
the text property to key parts so they can emit text even with no key
symbol.
Also, for keys that were not modified by the Function key because they
had no XKB key symbol name, modify them.
The Held state is for modifier that should be off when the corresponding
key is released. If the user presses the modifier key and a normal key,
it would be in this state. The modifier would continue to be active when
the user moves to a different key part (a cancel, e.g. from Fn to Alt)
afterwards. To fix this, add the HeldPressed and HeldLockedPressed
states that reset to the Released state when cancelled.
Keeping the keys pressed can confuse some compositors, and the key codes
may change. Release any keys that are pressed while the keymap is
changing, and press them again afterwards.
