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List:       lyx-cvs
Subject:    [LyX/master] Work around bug in QTextLine::xToCursor
From:       Jean-Marc Lasgouttes <lasgouttes () lyx ! org>
Date:       2017-03-31 15:03:44
Message-ID: 20170331150344.6E1BC28025C () lyx ! lyx ! org
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commit da590925cd6749587b9f500ecdaa457e34bc0f4a
Author: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date:   Fri Mar 31 16:56:06 2017 +0200

    Work around bug in QTextLine::xToCursor
    
    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.
---
 src/frontends/qt4/GuiFontMetrics.cpp |   29 +++++++++++++++++++++++++++--
 1 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/src/frontends/qt4/GuiFontMetrics.cpp b/src/frontends/qt4/GuiFontMetrics.cpp
index 33df3cf..585933a 100644
--- a/src/frontends/qt4/GuiFontMetrics.cpp
+++ b/src/frontends/qt4/GuiFontMetrics.cpp
@@ -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).

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