[Toybox] [PATCH] vi: changes to buffer drawing

[Rob Landley]

On 9/15/19 8:05 AM, Jarno Mäkipää wrote:
> Replaced: draw_str_until with lib/crunch_str() where possible
> 
> Removed: Unused char draw functions.
> 
> Implemented: crunch_nstr() which is crunch_str with additional check
> for byte length, this can be used to draw substrings or non null
> terminated strings. (This can be moved to lib/ if its useful for others)

Applied, but I note when I wrote crunch_str() I assumed that unicode was sane,
which was wrong.

UTF-8 is very well done. Unicode combining characters are as stupid as it's
possible to be: they TRAIL the printing character, meaning that you have a base
character that gets displayed, and then you redraw over it repeatedly as you get
each new modifier attaching to the _previous_ character you already drew, and
then you can't tell you've gone past your length allocation until you parse the
first character you _can't_ display in that space, which you then need to unget.

I thought combining characters were stored up and then applied to the _next_
character (which would have been the sane thing to do), and the measuring logic
works based on that assumption. So it probably won't display combining
characters on the last UTF8 character because the unicode committe is too dumb
to live.

Rob