This now returns true if any of the characters in the text belong to
the Arabic or Hebrew alphabet, or are one of the Unicode directional
formatting characters. This is just so the bidi machinery doesn't have
to run 100% of the time for 100% of the languages. I will also make it
so the Arabic language pack, as well as custom levels, have an RTL
attribute that always enables bidi (and does things like
right-alignment in textboxes and other design-flipping)
I'm now using SheenBidi to reorder RTL and bidirectional text properly
at text rendering time! For Arabic this is still missing reshaping, but
everything's looking really promising now!
The code changes are really non-invasive. The changes to Font.cpp are
absolutely minimal:
1305+ if (bidi_should_transform(text))
1306+ {
1307+ text = bidi_transform(text);
1308+ }
There's now a FontBidi.cpp, which implements these two functions,
notably bidi_transform(), which takes a UTF-8 encoded string and
returns another UTF-8 encoded string that has bidi reorderings and
reshapings applied.
In that function, SheenBidi gives us information about where in the
input string runs start and end, and on a basic level, all we need to
do there is to concatenate the parts together in the order that we're
given them, and to reverse the RTL runs (recognizable by odd levels).
As this is a proof-of-concept, bidi_should_transform() still always
returns true, applying the bidi algorithm to all languages and all
strings. I'm thinking of enabling bidi only when the language/font
metadata enables RTL (which could be for the interface or for a custom
level), or outside of that, at least when RTL characters are detected
(such as Arabic or Hebrew Unicode blocks).
