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Fix selection of unmarked RtL text

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With Qt 5.11 at least, RtL text will be drawn RtL even when the
(undocumented) flag Qt::TextForceLeftToRight is applied to the
QTextLayout object. This creates selection issues for Hebrew text
marked as English.

The solution is to do the same as in breakAt_helper, that is prepend
the string with a direction override unicode character.

Doing this requires to introduce a TEXTLAYOUT_OFFSET constant that has
to be used wisely to account for this extra character.

Fixes bug #11284.
This commit is contained in:
Jean-Marc Lasgouttes 2018-11-03 15:55:33 +00:00
parent 76e99e9a20
commit 1bed76e2a1
1 changed files with 24 additions and 4 deletions
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28
src/frontends/qt4/GuiFontMetrics.cpp
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@ -256,13 +256,27 @@ GuiFontMetrics::getTextLayout(docstring const & s, bool const rtl,
PROFILE_CACHE_MISS(getTextLayout);
auto const ptl = make_shared<QTextLayout>();
ptl->setCacheEnabled(true);
ptl->setText(toqstr(s));
QFont copy = font_;
copy.setWordSpacing(wordspacing);
ptl->setFont(copy);
// FIXME: This might not work in all cases. See breakAt_helper.
#if 1
/* Use unicode override characters to enforce drawing direction
* Source: http://www.iamcal.com/understanding-bidirectional-text/
*/
if (rtl)
// Right-to-left override: forces to draw text right-to-left
ptl->setText(QChar(0x202E) + toqstr(s));
else
// Left-to-right override: forces to draw text left-to-right
ptl->setText(QChar(0x202D) + toqstr(s));
#define TEXTLAYOUT_OFFSET 1
#else
// FIXME: This does not work with Qt 5.11 (ticket #11284).
// Note that both setFlags and the enums are undocumented
ptl->setFlags(rtl ? Qt::TextForceRightToLeft : Qt::TextForceLeftToRight);
ptl->setText(toqstr(s));
#define TEXTLAYOUT_OFFSET 0
#endif
ptl->beginLayout();
ptl->createLine();
ptl->endLayout();
@ -281,7 +295,9 @@ int GuiFontMetrics::pos2x(docstring const & s, int pos, bool const rtl,
* not be the same when there are high-plan unicode characters
* (bug #10443).
*/
int const qpos = toqstr(s.substr(0, pos)).length();
// TEXTLAYOUT_OFFSET accounts for a possible direction override
// character in front of the string.
int const qpos = toqstr(s.substr(0, pos)).length() + TEXTLAYOUT_OFFSET;
return static_cast<int>(tl->lineForTextPosition(qpos).cursorToX(qpos));
}
@ -323,7 +339,9 @@ int GuiFontMetrics::x2pos(docstring const & s, int & x, bool const rtl,
* (bug #10443).
*/
#if QT_VERSION < 0x040801 || QT_VERSION >= 0x050100
return qstring_to_ucs4(tl->text().left(qpos)).length();
int pos = qstring_to_ucs4(tl->text().left(qpos)).length();
// there may be a direction override character in front of the string.
return max(pos - TEXTLAYOUT_OFFSET, 0);
#else
/* Due to QTBUG-25536 in 4.8.1 <= Qt < 5.1.0, the string returned
* by QString::toUcs4 (used by qstring_to_ucs4) may have wrong
@ -333,6 +351,8 @@ int GuiFontMetrics::x2pos(docstring const & s, int & x, bool const rtl,
* worthwhile to implement a dichotomy search if this shows up
* under a profiler.
*/
// there may be a direction override character in front of the string.
qpos = max(qpos - TEXTLAYOUT_OFFSET, 0);
int pos = min(qpos, static_cast<int>(s.length()));
while (pos >= 0 && toqstr(s.substr(0, pos)).length() != qpos)
--pos;