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QString only uses UTF-16, not UCS-4

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This means that, when a string contains high-plane Unicode characters,
the length of a docstring and the corresponding QString will be
different: Qt will encode these characters using several 16bit
characters.

We have additionally to take into account QTBUG-25536, which implies
that sometimes qstring_to_ucs4(toqstr(s)) !=s. It is not clear whether
this bug can be a problem in other places.

Fixes bug #10443.
This commit is contained in:
Jean-Marc Lasgouttes 2016-11-02 17:42:56 +01:00
parent 8a9b376db7
commit 5d85a42bf0
1 changed files with 56 additions and 9 deletions
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65
src/frontends/qt4/GuiFontMetrics.cpp
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@ -206,7 +206,12 @@ int GuiFontMetrics::pos2x(docstring const & s, int const pos, bool const rtl,
double const wordspacing) const
{
QTextLayout const & tl = getTextLayout(s, font_, rtl, wordspacing);
return static_cast<int>(tl.lineForTextPosition(pos).cursorToX(pos));
/* Since QString is UTF-16 and docstring is UCS-4, the offsets may
* not be the same when there are high-plan unicode characters
* (bug #10443).
*/
int const qpos = toqstr(s.substr(0, pos)).length();
return static_cast<int>(tl.lineForTextPosition(qpos).cursorToX(qpos));
}
@ -214,10 +219,30 @@ int GuiFontMetrics::x2pos(docstring const & s, int & x, bool const rtl,
double const wordspacing) const
{
QTextLayout const & tl = getTextLayout(s, font_, rtl, wordspacing);
int pos = tl.lineForTextPosition(0).xToCursor(x);
int const qpos = tl.lineForTextPosition(0).xToCursor(x);
// correct x value to the actual cursor position.
x = static_cast<int>(tl.lineForTextPosition(0).cursorToX(pos));
x = static_cast<int>(tl.lineForTextPosition(0).cursorToX(qpos));
/* Since QString is UTF-16 and docstring is UCS-4, the offsets may
* not be the same when there are high-plan unicode characters
* (bug #10443).
*/
#if QT_VERSION < 0x040801 || QT_VERSION >= 0x050100
return qstring_to_ucs4(tl.text().left(qpos)).length();
#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
* length. We work around the problem by trying all docstring
* positions until the right one is found. This is slow only if
* there are many high-plane Unicode characters. It might be
* worthwhile to implement a dichotomy search if this shows up
* under a profiler.
*/
int pos = min(qpos, static_cast<int>(s.length()));
while (pos >= 0 && toqstr(s.substr(0, pos)).length() != qpos)
--pos;
LASSERT(pos > 0 || qpos == 0, /**/);
return pos;
#endif
}
@ -235,17 +260,17 @@ bool GuiFontMetrics::breakAt(docstring & s, int & x, bool const rtl, bool const
*/
// Unicode character ZERO WIDTH NO-BREAK SPACE
QChar const zerow_nbsp(0xfeff);
QString str = zerow_nbsp + toqstr(s) + zerow_nbsp;
QString qs = zerow_nbsp + toqstr(s) + zerow_nbsp;
#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
str = QChar(0x202E) + str;
qs = QChar(0x202E) + qs;
else
// Left-to-right override: forces to draw text left-to-right
str = QChar(0x202D) + str;
qs = QChar(0x202D) + qs;
int const offset = 2;
#else
// Alternative version that breaks with Qt5 and arabic text (#10436)
@ -254,7 +279,7 @@ bool GuiFontMetrics::breakAt(docstring & s, int & x, bool const rtl, bool const
int const offset = 1;
#endif
tl.setText(str);
tl.setText(qs);
tl.setFont(font_);
QTextOption to;
to.setWrapMode(force ? QTextOption::WrapAnywhere : QTextOption::WordWrap);
@ -267,8 +292,30 @@ bool GuiFontMetrics::breakAt(docstring & s, int & x, bool const rtl, bool const
if ((force && line.textLength() == offset) || int(line.naturalTextWidth()) > x)
return false;
x = int(line.naturalTextWidth());
// The offset is here to account for the extra leading characters.
s = s.substr(0, line.textLength() - offset);
/* Since QString is UTF-16 and docstring is UCS-4, the offsets may
* not be the same when there are high-plan unicode characters
* (bug #10443).
*/
// The variable `offset' is here to account for the extra leading characters.
// The ending character zerow_nbsp has to be ignored if the line is complete.
int const qlen = line.textLength() - offset - (line.textLength() == qs.length());
#if QT_VERSION < 0x040801 || QT_VERSION >= 0x050100
s = qstring_to_ucs4(qs.mid(offset, qlen));
#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
* length. We work around the problem by trying all docstring
* positions until the right one is found. This is slow only if
* there are many high-plane Unicode characters. It might be
* worthwhile to implement a dichotomy search if this shows up
* under a profiler.
*/
int len = min(qlen, static_cast<int>(s.length()));
while (len >= 0 && toqstr(s.substr(0, len)).length() != qlen)
--len;
LASSERT(len > 0 || qlen == 0, /**/);
s = s.substr(0, len);
#endif
return true;
}