DirectWrite font db: Fix writing system detection

The implementation here was accidentally missing from the
first commit. We use the OS/2 table for determining the writing system
support as intended by the font designer, and fall back to actually
checking the Unicode ranges if the table should be missing.

Change-Id: Ibfdf76c27f3a94eda2142b3e269a1ca30d4bc045
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 26 insertions, 0 deletions

diff --git a/src/gui/text/qplatformfontdatabase.cpp b/src/gui/text/qplatformfontdatabase.cpp
index 48ba8987f3..4ff2ad3a41 100644
--- a/src/gui/text/qplatformfontdatabase.cpp
+++ b/src/gui/text/qplatformfontdatabase.cpp
@@ -534,6 +534,32 @@ enum CsbBits {
 };
 
 /*!
+    Helper function that determines the writing system support based on the contents of the OS/2 table
+    in the font.
+
+    \since 6.0
+*/
+QSupportedWritingSystems QPlatformFontDatabase::writingSystemsFromOS2Table(const char *os2Table, size_t length)
+{
+    if (length >= 86)  {
+        quint32 unicodeRange[4] = {
+            qFromBigEndian<quint32>(os2Table + 42),
+            qFromBigEndian<quint32>(os2Table + 46),
+            qFromBigEndian<quint32>(os2Table + 50),
+            qFromBigEndian<quint32>(os2Table + 54)
+        };
+        quint32 codePageRange[2] = {
+            qFromBigEndian<quint32>(os2Table + 78),
+            qFromBigEndian<quint32>(os2Table + 82)
+        };
+
+        return writingSystemsFromTrueTypeBits(unicodeRange, codePageRange);
+    }
+
+    return QSupportedWritingSystems();
+}
+
+/*!
     Helper function that determines the writing systems support by a given
     \a unicodeRange and \a codePageRange.