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Adopt a 'belt and braces' approach to bidi forcing

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There are two techniques that I know of for forcing the direction of a
string, regardlessly of whether its contents is naturally LtR, RtL or
undecided.

1/ The unicode LTR/LTR override characters. This is supposed to be the
   clean way, however, it does not seem to work with Qt 5.14 (see
   #11691).

2/ The undocumented QTextLayout::setFlags method. This is used
   internally and allows to pass the (undocumented) flags
   Qt::TextForceRightToLeft and Qt::TextForceLeftToRight. This was
   used until we had issues with Qt 5.11 (see #11284).

In order to get the best of both worlds, this patch allows to enable
those two methods separately, and actually enables both at the same
time by default!

(hopefully) Fixes bug #11691.
This commit is contained in:
Jean-Marc Lasgouttes 2020-01-27 18:38:21 +01:00
parent a6f9c6ae43
commit 4d6041a7b6
1 changed files with 42 additions and 17 deletions
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59
src/frontends/qt/GuiFontMetrics.cpp
View File

@ -29,6 +29,25 @@
using namespace std;
using namespace lyx::support;
/* Define what mechanism is used to enforce text direction. Different
* methods work with different Qt versions. Here we try to use both
* methods together.
*/
// Define to use unicode override characters to force direction
#define BIDI_USE_OVERRIDE
// Define to use flag to force direction
#define BIDI_USE_FLAG
#ifdef BIDI_USE_OVERRIDE
# define BIDI_OFFSET 1
#else
# define BIDI_OFFSET 0
#endif
#if !defined(BIDI_USE_OVERRIDE) && !defined(BIDI_USE_FLAG)
# error "Define at least one of BIDI_USE_OVERRIDE or BIDI_USE_FLAG"
#endif
namespace std {
/*
@ -268,7 +287,15 @@ GuiFontMetrics::getTextLayout(docstring const & s, bool const rtl,
QFont copy = font_;
copy.setWordSpacing(wordspacing);
ptl->setFont(copy);
#if 1
#ifdef BIDI_USE_FLAG
/* Use undocumented flag to enforce drawing direction
* FIXME: This does not work with Qt 5.11 (ticket #11284).
*/
ptl->setFlags(rtl ? Qt::TextForceRightToLeft : Qt::TextForceLeftToRight);
#endif
#ifdef BIDI_USE_OVERRIDE
/* Use unicode override characters to enforce drawing direction
* Source: http://www.iamcal.com/understanding-bidirectional-text/
*/
@ -278,14 +305,10 @@ GuiFontMetrics::getTextLayout(docstring const & s, bool const rtl,
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();
@ -304,9 +327,9 @@ int GuiFontMetrics::pos2x(docstring const & s, int pos, bool const rtl,
* not be the same when there are high-plan unicode characters
* (bug #10443).
*/
// TEXTLAYOUT_OFFSET accounts for a possible direction override
// BIDI_OFFSET accounts for a possible direction override
// character in front of the string.
int const qpos = toqstr(s.substr(0, pos)).length() + TEXTLAYOUT_OFFSET;
int const qpos = toqstr(s.substr(0, pos)).length() + BIDI_OFFSET;
return static_cast<int>(tl->lineForTextPosition(qpos).cursorToX(qpos));
}
@ -350,7 +373,7 @@ int GuiFontMetrics::x2pos(docstring const & s, int & x, bool const rtl,
#if QT_VERSION < 0x040801 || QT_VERSION >= 0x050100
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);
return max(pos - BIDI_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
@ -361,7 +384,7 @@ int GuiFontMetrics::x2pos(docstring const & s, int & x, bool const rtl,
* under a profiler.
*/
// there may be a direction override character in front of the string.
qpos = max(qpos - TEXTLAYOUT_OFFSET, 0);
qpos = max(qpos - BIDI_OFFSET, 0);
int pos = min(qpos, static_cast<int>(s.length()));
while (pos >= 0 && toqstr(s.substr(0, pos)).length() != qpos)
--pos;
@ -407,7 +430,14 @@ GuiFontMetrics::breakAt_helper(docstring const & s, int const x,
// Unicode character ZERO WIDTH NO-BREAK SPACE
QChar const zerow_nbsp(0xfeff);
QString qs = zerow_nbsp + toqstr(s) + zerow_nbsp;
#if 1
#ifdef BIDI_USE_FLAG
/* Use undocumented flag to enforce drawing direction
* FIXME: This does not work with Qt 5.11 (ticket #11284).
*/
tl.setFlags(rtl ? Qt::TextForceRightToLeft : Qt::TextForceLeftToRight);
#endif
#ifdef BIDI_USE_OVERRIDE
/* Use unicode override characters to enforce drawing direction
* Source: http://www.iamcal.com/understanding-bidirectional-text/
*/
@ -417,13 +447,8 @@ GuiFontMetrics::breakAt_helper(docstring const & s, int const x,
else
// Left-to-right override: forces to draw text left-to-right
qs = QChar(0x202D) + qs;
int const offset = 2;
#else
// Alternative version that breaks with Qt5 and arabic text (#10436)
// Note that both setFlags and the enums are undocumented
tl.setFlags(rtl ? Qt::TextForceRightToLeft : Qt::TextForceLeftToRight);
int const offset = 1;
#endif
int const offset = 1 + BIDI_OFFSET;
tl.setText(qs);
tl.setFont(font_);