Fix spacing issues on ligatures as seen on #36.

[HealsCodes]

This PR is a response to the new issues reported in #36, currently WIP - see checklist below.

The idea is to do a proper analysis of the ligatures (if any) and try to avoid double character draws / moving spaces etc.

code changes:

• compare string with- and without ligatures
• skip positions as needed
• add compatibility with emoji
• add a note to the preference to indicate the cursorline / relativenumber requirement.

testing:

• instruments: no leaks?
• local test with and without listchars
• local test with and without cursorline (to force / relax draws)
• collect feedback from affected users (see Support for font ligatures #36)

[splhack]

Unfortunately, ligature support breaks Emoji (for example, '🐱') rendering. Surrogate pairs, perhaps?

[HealsCodes]

That feature got in after my first PR - I'll have a look at it..

Am 08.11.2015 um 04:59 schrieb Kazuki Sakamoto notifications@github.com:

Unfortunately, ligature support breaks Emoji rendering. Surrogate pairs, perhaps?

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[HealsCodes]

@splhack - I think I have something working for both of us:

[splhack]

@Shirk 👍

[jordwalke]

The result of this diff is that MacVim has a reasonable user experience for ligature fonts if you have cursorline enabled. There are still remaining issues being tracked, but I can confirm that this fixes bugs that were currently already merged into master.

[jordwalke]

Any update on this?

[HealsCodes]

@jordwalke - I'm undecided..

I could remove the [WIP] for this part and convince @douglasdrumond to merge but it would still only work for people with either cursorline or relativenumber enabled.

So I'm debating with myself whether to add a notice to the option dialog ("currently cursorline or relativenumber setting is required for this feature") or go looking for a way to get vim to always redraw the active window when it has ligatures enabled.

I've been looking around the MacVim-gui design and there seems to be no easy way for the GUI process to communicate to the back-end process that the active (VIM)window needs redraw.

[jordwalke]

My justification for suggesting this be merged is that it fixes bugs that are in master and seems to not make anything else worse. Of course, I'd love for everything to be redrawn at the right time perfectly with or without cursorline. But there are many people who would do anything for ligatures. For those people, with this implementation, it's pretty easy to add a little tweak to their vimrc:

set cursorline
highlight CursorLine guibg=NONE

Not to downplay how awesome it would be for this to not be necessary.

[chdiza]

What will happen if someone does not want ligatures rendered, does not have a font with ligatures, but has cursorline or relativenumber enabled? Is their experience going to be bogged down with constant redraws? If so, then this should either not be merged, or there needs to be a checkbox in the prefs, OFF by default, to enable this ligature stuff.

[jordwalke]

There is certainly an option (already in master, in fact) - @Shirk will have to confirm that it actually has no impact when toggled off - but I can't even detect a perf impact when toggled on (on my very weak macbook).

[HealsCodes]

@chdiza - ligatures have been merged already in a previous (see #36) and have no impact at all since they are in no way related to cursorline or relativenumber. The only relation between them is that if you happen to have enabled cursorline or relativenumber ligatures will be displayed properly since in those cases VIM will always redraw the whole current line if the cursor moves up / down (which is not new but the default behavior for both options).

[EDIT] rephrased to prevent this comment from sounding harsh which it wasn't supposed to be (it was a long day..)

[HealsCodes]

@jordwalke for now I'm going with the "add a note the preferences" way so this PR has a chance of getting merged quickly.

@douglasdrumond - if you wouldn't mind to have a look.