fullscreen transparent keyboard

[Chuck Norris]

I think it would be nice to have fullscreen transparent keyboard instead
of small keyboard in the bottom that eats screen space. So anybody know
application that fit my needs? I googled... but found nothing
interesting. I've begun developing my own virtual keyboard. I've created
sample gtk application - transparent window with one button that sends
"a" to X. Will my keyboard be useful for anybody if I'll continue
creating it?