I get that this is quite a specialised concern, but I've already added 'Greek (polytonic)' to my keyboard layouts, and it works for typing certain accents and characters. I can easily type ά, ὰ, ἀ, ἁ, ᾳ, ᾶ, ᾱ and ᾰ (for any vowel) by using dead keys on [;], ['], [ and ], but this seems to be it.
I need to have some key combination for characters with an accent and a breathing/iota subscript, such as ἄ, ἆ and ᾇ. I've tried a selection of combinations which are used for the Windows polytonic layout, as well as the combinations mentioned in this document: https://docs.google.com/document/d/1oiK5KraVvob6fAEhcVjwI99RlWtnBLiSGgDFs96qrbk/edit, but the only time that pressing two keys beforehand seems to work is Shift+;/' for ἀ/ἁ.
Is there some way that I have to set up AltGr to work in the way the writer of that document uses it? I've set up the 'Compose key' to be AltGr and 'Alternative Characters key' to be Right Ctrl, but neither of those seem to do anything on the Greek keyboard. The Keyboard Layout Chart doesn't suggest there's any way of typing the characters I want.
Sorry if there's a really obvious answer to this, I'm still getting used to Ubuntu, but it's a big problem for me if there isn't a way to type these characters. I'm reluctant to try this: http://frame-poythress.org/keyboard-entry-of-polytonic-greek-and-biblical-hebrew-in-gnulinux-2014/, as the layout of the bare characters isn't what I'm used to. If necessary, would I be able to set up keyboard combinations for these characters?
χάριν ἐχω ὑμῖν in advance!