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Work around bug in QTextLine::xToCursor

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With RtL text, the method can be non-monotonic wrt x value (which is a
Qt bug). To work around this, we check whether positions adjacent to
those returned by xToCursor look better. Depending on whether the new
x position is too small or too large, we look backward or forward for
a better solution.

The performance is probably not great, but this is only needed for
user interactions, so the performance penalty should not be a problem.

Fixes #10569.
This commit is contained in:
Jean-Marc Lasgouttes 2017-03-31 16:56:06 +02:00
parent db7054da9f
commit da590925cd
1 changed files with 27 additions and 2 deletions
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29
src/frontends/qt4/GuiFontMetrics.cpp
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@ -272,9 +272,34 @@ int GuiFontMetrics::x2pos(docstring const & s, int & x, bool const rtl,
double const wordspacing) const
{
shared_ptr<QTextLayout const> tl = getTextLayout(s, rtl, wordspacing);
int const qpos = tl->lineForTextPosition(0).xToCursor(x);
QTextLine const & tline = tl->lineForTextPosition(0);
int qpos = tline.xToCursor(x);
int newx = static_cast<int>(tline.cursorToX(qpos));
// The value of qpos may be wrong in rtl text (see ticket #10569).
// To work around this, let's have a look at adjacent positions to
// see whether we find closer matches.
if (rtl && newx < x) {
while (qpos > 0) {
int const xm = static_cast<int>(tline.cursorToX(qpos - 1));
if (abs(xm - x) < abs(newx - x)) {
--qpos;
newx = xm;
} else
break;
}
} else if (rtl && newx > x) {
while (qpos < tline.textLength()) {
int const xp = static_cast<int>(tline.cursorToX(qpos + 1));
if (abs(xp - x) < abs(newx - x)) {
++qpos;
newx = xp;
} else
break;
}
}
// correct x value to the actual cursor position.
x = static_cast<int>(tl->lineForTextPosition(0).cursorToX(qpos));
x = newx;
/* 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).