Fix font height metrics with embedded bitmaps

For fonts with embedded bitmaps, we cannot trust the HHEA and
OS/2 tables, since there are a different set of font metrics
in the EBLC/CBLC tables for each of the predefined bitmap
sizes.

In this case, we can safely fall back to the metrics returned
by the system, as the inconsistency we were originally fixing
was only between OS/2 and HHEA and will not matter for the
bitmap fonts.

This patch also simplifies the code path through the font
engines a bit. Instead of setting the system metrics in the
processHheaTable() function when the table cannot be found,
we instead always fetch the system metrics at the very start
of initializeHeightMetrics() and then override if there are
no embedded bitmaps, and if the HHEA and OS/2 tables are
available. This also reduces the number of virtual functions
needed to sort out the height metrics.

Fixes: QTBUG-83754
Change-Id: Ib9dc6fc6cf972e48209a4a272469d2b4bd1ebffe
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/gui/text/qfontengine.cpp

@@ -450,13 +450,14 @@ bool QFontEngine::processHheaTable() const
 
 void QFontEngine::initializeHeightMetrics() const
 {
-    if (!processHheaTable()) {
-        qWarning() << "Cannot determine metrics for font" << fontDef.family;
-        m_ascent = m_descent = m_leading = 1;
-    }
+    bool hasEmbeddedBitmaps = !getSfntTable(MAKE_TAG('E', 'B', 'L', 'C')).isEmpty() || !getSfntTable(MAKE_TAG('C', 'B', 'L', 'C')).isEmpty();
+    if (!hasEmbeddedBitmaps) {
+        // Get HHEA table values if available
+        processHheaTable();
 
-    // Allow OS/2 metrics to override if present
-    processOS2Table();
+        // Allow OS/2 metrics to override if present
+        processOS2Table();
+    }
 
     m_heightMetricsQueried = true;
 }

src/gui/text/qfontengine_p.h

@@ -375,8 +375,8 @@ protected:
     mutable bool m_heightMetricsQueried;
 
     virtual void initializeHeightMetrics() const;
-    virtual bool processHheaTable() const;
-    virtual bool processOS2Table() const;
+    bool processHheaTable() const;
+    bool processOS2Table() const;
 
 private:
     struct GlyphCacheEntry {

src/platformsupport/fontdatabases/freetype/qfontengine_ft.cpp

@@ -1243,6 +1243,10 @@ int QFontEngineFT::synthesized() const
 
 void QFontEngineFT::initializeHeightMetrics() const
 {
+    m_ascent = QFixed::fromFixed(metrics.ascender);
+    m_descent = QFixed::fromFixed(-metrics.descender);
+    m_leading = QFixed::fromFixed(metrics.height - metrics.ascender + metrics.descender);
+
     QFontEngine::initializeHeightMetrics();
 
     if (scalableBitmapScaleFactor != 1) {
@@ -1252,17 +1256,6 @@ void QFontEngineFT::initializeHeightMetrics() const
     }
 }
 
-bool QFontEngineFT::processHheaTable() const
-{
-    if (!QFontEngine::processHheaTable()) {
-        m_ascent = QFixed::fromFixed(metrics.ascender);
-        m_descent = QFixed::fromFixed(-metrics.descender);
-        m_leading = QFixed::fromFixed(metrics.height - metrics.ascender + metrics.descender);
-    }
-
-    return true;
-}
-
 QFixed QFontEngineFT::capHeight() const
 {
     TT_OS2 *os2 = (TT_OS2 *)FT_Get_Sfnt_Table(freetype->face, ft_sfnt_os2);

src/platformsupport/fontdatabases/freetype/qfontengine_ft_p.h

@@ -192,7 +192,6 @@ private:
     int synthesized() const override;
 
     void initializeHeightMetrics() const override;
-    bool processHheaTable() const override;
     QFixed capHeight() const override;
     QFixed xHeight() const override;
     QFixed averageCharWidth() const override;

src/platformsupport/fontdatabases/mac/qfontengine_coretext.mm

@@ -381,15 +381,13 @@ QT_WARNING_POP
     return ret;
 }
 
-bool QCoreTextFontEngine::processHheaTable() const
+void QCoreTextFontEngine::initializeHeightMetrics() const
 {
-    if (!QFontEngine::processHheaTable()) {
-        m_ascent = QFixed::fromReal(CTFontGetAscent(ctfont));
-        m_descent = QFixed::fromReal(CTFontGetDescent(ctfont));
-        m_leading = QFixed::fromReal(CTFontGetLeading(ctfont));
-    }
+    m_ascent = QFixed::fromReal(CTFontGetAscent(ctfont));
+    m_descent = QFixed::fromReal(CTFontGetDescent(ctfont));
+    m_leading = QFixed::fromReal(CTFontGetLeading(ctfont));
 
-    return true;
+    QFontEngine::initializeHeightMetrics();
 }
 
 QFixed QCoreTextFontEngine::capHeight() const

src/platformsupport/fontdatabases/mac/qfontengine_coretext_p.h

@@ -139,7 +139,7 @@ protected:
     bool hasColorGlyphs() const;
     bool shouldAntialias() const;
     bool shouldSmoothFont() const;
-    bool processHheaTable() const override;
+    void initializeHeightMetrics() const override;
 
     QCFType<CTFontRef> ctfont;
     QCFType<CGFontRef> cgFont;

src/platformsupport/fontdatabases/windows/qwindowsfontengine.cpp

@@ -610,15 +610,13 @@ void QWindowsFontEngine::getGlyphBearings(glyph_t glyph, qreal *leftBearing, qre
 }
 #endif // Q_CC_MINGW
 
-bool QWindowsFontEngine::processHheaTable() const
+void QWindowsFontEngine::initializeHeightMetrics() const
 {
-    if (!QFontEngine::processHheaTable()) {
-        m_ascent = tm.tmAscent;
-        m_descent = tm.tmDescent;
-        m_leading = tm.tmExternalLeading;
-    }
+    m_ascent = tm.tmAscent;
+    m_descent = tm.tmDescent;
+    m_leading = tm.tmExternalLeading;
 
-    return true;
+    QFontEngine::initializeHeightMetrics();
 }
 
 bool QWindowsFontEngine::hasUnreliableGlyphOutline() const

src/platformsupport/fontdatabases/windows/qwindowsfontengine_p.h

@@ -130,7 +130,7 @@ public:
     void setUniqueFamilyName(const QString &newName) { uniqueFamilyName = newName; }
 
 protected:
-    bool processHheaTable() const override;
+    void initializeHeightMetrics() const override;
 
 private:
     QWindowsNativeImage *drawGDIGlyph(HFONT font, glyph_t, int margin, const QTransform &xform,

src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite.cpp

@@ -343,18 +343,16 @@ QString QWindowsFontEngineDirectWrite::filenameFromFontFile(IDWriteFontFile *fon
     return ret;
 }
 
-bool QWindowsFontEngineDirectWrite::processHheaTable() const
+void QWindowsFontEngineDirectWrite::initializeHeightMetrics() const
 {
-    if (!QFontEngine::processHheaTable()) {
-        DWRITE_FONT_METRICS metrics;
-        m_directWriteFontFace->GetMetrics(&metrics);
+    DWRITE_FONT_METRICS metrics;
+    m_directWriteFontFace->GetMetrics(&metrics);
 
-        m_ascent = DESIGN_TO_LOGICAL(metrics.ascent);
-        m_descent = DESIGN_TO_LOGICAL(metrics.descent);
-        m_leading = DESIGN_TO_LOGICAL(metrics.lineGap);
-    }
+    m_ascent = DESIGN_TO_LOGICAL(metrics.ascent);
+    m_descent = DESIGN_TO_LOGICAL(metrics.descent);
+    m_leading = DESIGN_TO_LOGICAL(metrics.lineGap);
 
-    return true;
+    QFontEngine::initializeHeightMetrics();
 }
 
 void QWindowsFontEngineDirectWrite::collectMetrics()

src/platformsupport/fontdatabases/windows/qwindowsfontenginedirectwrite_p.h

@@ -122,7 +122,7 @@ public:
 
     void setUniqueFamilyName(const QString &newName) { m_uniqueFamilyName = newName; }
 
-    bool processHheaTable() const override;
+    void initializeHeightMetrics() const override;
 
 private:
     QImage imageForGlyph(glyph_t t, QFixed subPixelPosition, int margin, const QTransform &xform, const QColor &color = QColor());