Fix overlapping text for Osaka font on macOS

The Osaka font on macOS has all zeroes in the OS/2 table, probably
because it is not intended to be cross-platform. In Qt 6 (since
f761ad3cd9ad1252f24b76ae413298dc7bed8af3) we are trying using the
same vertical metrics on all platforms, but this only works if
they are valid.

To work around this issue, we detect the case when ascent/descent
values are both 0, since this is very unlikely to be intentional,
so we fall back to the system-provided ascent and descent in these
cases.

Adding the test also revealed that we had missed the check for
a macOS-specific bitmap font format when skipping the check for
bitmap fonts in 7a18b7e2c2394b2b2cc95833c755f91193d9ba2e.

[ChangeLog][macOS][Text] Fixed a problem where using the Osaka
font would lead to overlapping text.

Pick-to: 6.2
Fixes: QTBUG-96880
Change-Id: Ifea7918641a68829e8f5ef20a4fb61c0a7e5b757
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 14 insertions, 1 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 10d3b5d2cb..80c28a376a 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -436,6 +436,10 @@ bool QFontEngine::processHheaTable() const
         qint16 descent = qFromBigEndian<qint16>(hhea.constData() + 6);
         qint16 leading = qFromBigEndian<qint16>(hhea.constData() + 8);
 
+        // Some fonts may have invalid HHEA data. We detect this and bail out.
+        if (ascent == 0 && descent == 0)
+            return false;
+
         QFixed unitsPerEm = emSquareSize();
         m_ascent = QFixed::fromReal(ascent * fontDef.pixelSize) / unitsPerEm;
         m_descent = -QFixed::fromReal(descent * fontDef.pixelSize) / unitsPerEm;
@@ -450,7 +454,10 @@ bool QFontEngine::processHheaTable() const
 
 void QFontEngine::initializeHeightMetrics() const
 {
-    bool hasEmbeddedBitmaps = !getSfntTable(MAKE_TAG('E', 'B', 'L', 'C')).isEmpty() || !getSfntTable(MAKE_TAG('C', 'B', 'L', 'C')).isEmpty();
+    bool hasEmbeddedBitmaps =
+            !getSfntTable(MAKE_TAG('E', 'B', 'L', 'C')).isEmpty()
+            || !getSfntTable(MAKE_TAG('C', 'B', 'L', 'C')).isEmpty()
+            || !getSfntTable(MAKE_TAG('b', 'd', 'a', 't')).isEmpty();
     if (!hasEmbeddedBitmaps) {
         // Get HHEA table values if available
         processHheaTable();
@@ -476,10 +483,16 @@ bool QFontEngine::processOS2Table() const
         enum { USE_TYPO_METRICS = 0x80 };
         QFixed unitsPerEm = emSquareSize();
         if (fsSelection & USE_TYPO_METRICS) {
+            // Some fonts may have invalid OS/2 data. We detect this and bail out.
+            if (typoAscent == 0 && typoDescent == 0)
+                return false;
             m_ascent = QFixed::fromReal(typoAscent * fontDef.pixelSize) / unitsPerEm;
             m_descent = -QFixed::fromReal(typoDescent * fontDef.pixelSize) / unitsPerEm;
             m_leading = QFixed::fromReal(typoLineGap * fontDef.pixelSize) / unitsPerEm;
         } else {
+            // Some fonts may have invalid OS/2 data. We detect this and bail out.
+            if (winAscent == 0 && winDescent == 0)
+                return false;
             m_ascent = QFixed::fromReal(winAscent * fontDef.pixelSize) / unitsPerEm;
             m_descent = QFixed::fromReal(winDescent * fontDef.pixelSize) / unitsPerEm;
         }