In Korean text, they typically can use both the "Western" style of
word wrapping, i.e. breaking on spaces, as well as the East-Asian
style of potentially breaking between all syllables. However,
the Unicode Line Breaking Algorithm, TR14 defaults to breaks on
syllables and specifies a possible tailoring where Hangul is
mapped to the AL class instead:
"When Korean uses SPACE for line breaking, the classes in rule
LB26, as well as characters of class ID, are often tailored to AL"
When using Qt, the user would expect the WordWrap wrap mode to
break between words in Korean. If you want the syllable-based
text layout, you would use WrapAnywhere, probably accompanied
by line justification.
To avoid breaking QTextBoundaryFinder and other potential clients
of QUnicodeTools which depend on getting the precise Unicode
data from the algorithm, we do this by passing a flag from
QTextEngine when initializing the attributes. This way, it
can also be made optional later on, if we decide there is
a reason to add an additional wrap mode specifically to
handle cases like this.
[ChangeLog][Important Behavioral Change] WrapWord now
correctly prefers line breaks between words in Korean text.
WrapAnywhere can still be used to get breaks between syllables
instead.
Done-with: Alexey Turitsyn <alexey.turitsyn@lge.com>
Task-number: QTBUG-47644
Change-Id: I37b45cea2995db7fc2b61e3a0cc681bbdc334678
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
d1bab5b1e3