Status: New
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 1745 by [email protected]: Qt 5 input method plugin badly maps
text attributes to QTextCharFormat
https://code.google.com/p/ibus/issues/detail?id=1745
What version of the product are you using? On what operating system?
OS (Linux distributions, UNIX or ...): Fedora 21 Alpha
Architecture (i386, x86_64): x86_64
IBus version: 1.5.9
Input method name and version: ibus-hangul, 1.4.2
Python version: 2.7.8
dbus version: 1.8.6
dbus-python version: 1.2.0
gtk version (if bug is about gtk applications):
qt version (if bug is about qt applications): Qt 5.3 branch tip (reports as
5.3.3)
When I am typing a Hangul block into a Qt 5 app, the input method plugin
will construct multiple QInputMethodEvents and send them to the active
widget with the correct pre-edit text before the block is complete and
committed.
Unfortunately, the attribute list for each pre-commit QInputMethodEvent
contains multiple attributes of type TextFormat for the same range. In the
Qt 5.3 docs, this is listed as undefined behavior: "If several are
specified for any character in the string the behaviour is undefined."
The reason this happens is that the plugin receives a text event from ibus
with multiple color text attributes with different types, one for the
foreground and one for the background. It then converts both of those into
QTextCharFormats and adds them to the attribute list.
This isn't a good idea, both because Qt states the behavior for this is
undefined, but also because it's not how QTextCharFormat works: A
QTextCharFormat can have both a foreground and a background brush.
What the plugin should do instead is combine both of the ibus attributes
into a single QTextCharFormat with foreground and background set.
This behavior currently badly breaks pre-edit text in KDE's Kate text
editor: https://bugs.kde.org/show_bug.cgi?id=339467
Kate applies both of the QTextCharFormats to the text, and because the
second text attribute has NoBrush as pen() the text is rendered invisible.
Note that Kate cannot use QTextFormat::merge() to combine them, because it
can't know which is the foreground and which is the background, so the
operand order is unclear. It could ignore the second QTextCharFormat, but
then it would lose the background color information. That's why this really
needs to be fixed in the plugin.
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