[LyX/master] str_metrics: Prevent clipping of chars with negative bearing

[Vincent van Ravesteijn]

commit c313b1c8eb01c85775e62a8675fa569d2c2aac2c
Author: Vincent van Ravesteijn <v...@lyx.org>
Date:   Tue Jan 6 18:48:19 2015 +0100

    str_metrics: Prevent clipping of chars with negative bearing
    
    This happens when part of the word is selected.
    
    To reproduce:
    1. Start a new document
    2. Type "af"
    3. Select 'a'
    4. Observe that the right part of the 'f' is clipped away.
    
    This patch uses QRegion to set a clip region that is everything except
    the part that is drawn in another color.
    
    Fixes: #9223.

diff --git a/src/frontends/qt4/GuiPainter.cpp b/src/frontends/qt4/GuiPainter.cpp
index 5730819..95ab52a 100644
--- a/src/frontends/qt4/GuiPainter.cpp
+++ b/src/frontends/qt4/GuiPainter.cpp
@@ -465,15 +465,16 @@ int GuiPainter::text(int x, int y, docstring const & str, 
Font const & f,
        // First the part in other color
        Color const orig = fi.realColor();
        fi.setPaintColor(other);
-       setClipRect(QRect(x + xmin, y - ascent, xmax - xmin, height));
+       QRegion const clip(x + xmin, y - ascent, xmax - xmin, height);
+       setClipRegion(clip);
        int const textwidth = text(x, y, str, fi, rtl);
 
        // Then the part in normal color
-       // Note that in Qt5, it is not possible to use Qt::UniteClip
+       // Note that in Qt5, it is not possible to use Qt::UniteClip,
+       // therefore QRegion is used.
        fi.setPaintColor(orig);
-       setClipRect(QRect(x, y - ascent, xmin, height));
-       text(x, y, str, fi, rtl);
-       setClipRect(QRect(x + xmax, y - ascent, textwidth - xmax, height));
+       QRegion region(viewport());
+       setClipRegion(region - clip);
        text(x, y, str, fi, rtl);
        setClipping(false);