Fix combining marks handling in Core Text shaper

For fonts without combined glyph for combinations like U+0062 U+0300,
Core Text will return glyph sequences like <b> <`>, the latter will
have advance_x = 0, advance_y = <positive value> to keep it above
the previous glyph. To get correct positioning in flipped coordinate,
we need to store the negative y advance in Qt.

Task-number: QTBUG-15675
Reviewed-by: Eskil

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/text/qfontengine_coretext.mm b/src/gui/text/qfontengine_coretext.mm
index 2ae60b15f4..0209689473 100644
--- a/src/gui/text/qfontengine_coretext.mm
+++ b/src/gui/text/qfontengine_coretext.mm
@@ -234,7 +234,8 @@ bool QCoreTextFontEngineMulti::stringToCMap(const QChar *str, int len, QGlyphLay
                 int idx = rtlOffset + rtlSign * i;
                 outGlyphs[idx] = tmpGlyphs[i] | fontIndex;
                 outAdvances_x[idx] = QFixed::fromReal(tmpPoints[i + 1].x - tmpPoints[i].x);
-                outAdvances_y[idx] = QFixed::fromReal(tmpPoints[i + 1].y - tmpPoints[i].y);
+                // Use negative y advance for flipped coordinate system
+                outAdvances_y[idx] = QFixed::fromReal(tmpPoints[i].y - tmpPoints[i + 1].y);
 
                 if (fontDef.styleStrategy & QFont::ForceIntegerMetrics) {
                     outAdvances_x[idx] = outAdvances_x[idx].round();