We weren't quite right with handling the cursor around double-width
characters. We're now a bit more robust at this because we're
clustering and taking pains to consider the printable width of the
cell as well as the width of the shaped (eg: with contextual ligatures)
glyph.
There may still be issues with contextual ligatures of length 3,
but I haven't managed to nail down exactly the issue yet.
Actually, the flicker was caused by the back pixel setting on the
window; I spent a long time running this down and finally got the
clue from this crusade against flicker:
http://www.ruska.it/michal/flicker.html
The spacing between glyphs seems too wide. Need to figure this out.
A bunch of the integer vs float changes in this diff were a result
of trying to run this down, but success has been limited, and in fact
the spacing has increased as a result of making this more correct(!)
Initially I wanted to make the font code separate from
the main wterm executable in the hope that it would be
reusable. However, we do need to be able to reach in
to both the font implementation and the SDL texture
implementation in order to capture the glyph data
into textures, so let's just embrace it all being
in the same crate.
