Implement QFontEngineS60::emSquareSize()

Some glyph position tweaks during the shaping phase require
the "Units per Em" information for the font. QFontEngineS60
did not reimplement emSquareSize(), therefore, some combined
glyphs were rendered incorrectly (see QTBUG-10725)

This patch implements QFontEngineS60::emSquareSize()
Since Symbian does not provide the "Units per Em" via public
Api, we have to pick that out of the 'head' font table.
The value is cached per font.

Task-Number: QTBUG-10725
Reviewed-by: Eskil Abrahamsen Blomfeldt

1 files changed, 26 insertions, 0 deletions

diff --git a/src/gui/text/qfontengine_s60.cpp b/src/gui/text/qfontengine_s60.cpp
index 32fcb82a83..824a8e233e 100644
--- a/src/gui/text/qfontengine_s60.cpp
+++ b/src/gui/text/qfontengine_s60.cpp
@@ -41,6 +41,7 @@
 
 #include "qfontengine_s60_p.h"
 #include "qtextengine_p.h"
+#include "qendian.h"
 #include "qglobal.h"
 #include <private/qapplication_p.h>
 #include "qimage.h"
@@ -176,6 +177,24 @@ CFont *QSymbianTypeFaceExtras::fontOwner() const
     return m_cFont;
 }
 
+QFixed QSymbianTypeFaceExtras::unitsPerEm() const
+{
+    if (m_unitsPerEm.value() != 0)
+        return m_unitsPerEm;
+    const QByteArray head = getSfntTable(MAKE_TAG('h', 'e', 'a', 'd'));
+    const int unitsPerEmOffset = 18;
+    if (head.size() > unitsPerEmOffset + sizeof(quint16)) {
+        const uchar* tableData = reinterpret_cast<const uchar*>(head.constData());
+        const uchar* unitsPerEm = tableData + unitsPerEmOffset;
+        m_unitsPerEm = qFromBigEndian<quint16>(unitsPerEm);
+    } else {
+        // Bitmap font? Corrupt font?
+        // We return -1 and let the QFontEngineS60 return the pixel size.
+        m_unitsPerEm = -1;
+    }
+    return m_unitsPerEm;
+}
+
 // duplicated from qfontengine_xyz.cpp
 static inline unsigned int getChar(const QChar *str, int &i, const int len)
 {
@@ -248,6 +267,13 @@ QFontEngineS60::~QFontEngineS60()
     releaseFont(m_scaledFont);
 }
 
+QFixed QFontEngineS60::emSquareSize() const
+{
+    const QFixed unitsPerEm = m_extras->unitsPerEm();
+    return unitsPerEm.toInt() == -1 ?
+                QFixed::fromReal(m_originalFontSizeInPixels) : unitsPerEm;
+}
+
 bool QFontEngineS60::stringToCMap(const QChar *characters, int len, QGlyphLayout *glyphs, int *nglyphs, QTextEngine::ShaperFlags flags) const
 {
     if (*nglyphs < len) {