Make cache of opentype tables in Harfbuzz face lazy

The mechanism in fontconfig which determines if a certain character
is available (FcCharSetHasChar()) may give false positives, in which
case we would load and unload those fonts per every char for which
FC gave us a false positive. This was a major performance regression.
Specifically the false positives happened when looking at e.g.
italic variants of certain multilingual fonts, since we only check
the charset of the font family as a whole and not of the specific variant,
which may only support a subset of the chars.

To optimize this, we remove the deletion of the font engines after
loading them, but also wait with loading the opentype tables until
they are actually needed. This means that for the false positives,
we will load the font, but the cached data for each unused font will
be much smaller.

Change-Id: Idfc794401a2080da5946bf65204eb947aeb635ed
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

src/3rdparty/harfbuzz/src/harfbuzz-shaper.cpp

@@ -995,7 +995,7 @@ static HB_Stream getTableStream(void *font, HB_GetFontTableFunc tableFunc, HB_Ta
     return stream;
 }
 
-HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc)
+HB_Face HB_AllocFace(void *font, HB_GetFontTableFunc tableFunc)
 {
     HB_Face face = (HB_Face )malloc(sizeof(HB_FaceRec));
     if (!face)
@@ -1012,6 +1012,30 @@ HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc)
     face->tmpLogClusters = 0;
     face->glyphs_substituted = false;
     face->buffer = 0;
+    face->font_for_init = font;
+    face->get_font_table_func = tableFunc;
+
+    return face;
+}
+
+HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc)
+{
+    HB_Face face = HB_AllocFace(font, tableFunc);
+    if (face)
+        face = HB_LoadFace(face);
+    return face;
+}
+
+HB_Face HB_LoadFace(HB_Face face)
+{
+    void *font = face->font_for_init;
+    if (!font)
+        return face;
+
+    HB_GetFontTableFunc tableFunc = face->get_font_table_func;
+
+    face->get_font_table_func = 0;
+    face->font_for_init = 0;
 
     HB_Error error = HB_Err_Ok;
     HB_Stream stream;

src/3rdparty/harfbuzz/src/harfbuzz-shaper.h

@@ -201,6 +201,8 @@ typedef struct {
     hb_bitfield combiningClass  :8;
 } HB_GlyphAttributes;
 
+typedef HB_Error (*HB_GetFontTableFunc)(void *font, HB_Tag tag, HB_Byte *buffer, HB_UInt *length);
+
 typedef struct HB_FaceRec_ {
     HB_Bool isSymbolFont;
 
@@ -217,11 +219,15 @@ typedef struct HB_FaceRec_ {
     unsigned int *tmpLogClusters;
     int length;
     int orig_nglyphs;
+    void *font_for_init;
+    HB_GetFontTableFunc get_font_table_func;
 } HB_FaceRec;
 
-typedef HB_Error (*HB_GetFontTableFunc)(void *font, HB_Tag tag, HB_Byte *buffer, HB_UInt *length);
+
 
 HB_Face HB_NewFace(void *font, HB_GetFontTableFunc tableFunc);
+HB_Face HB_AllocFace(void *font, HB_GetFontTableFunc tableFunc);
+HB_Face HB_LoadFace(HB_Face face);
 void HB_FreeFace(HB_Face face);
 
 typedef struct {

src/corelib/tools/qharfbuzz.cpp

@@ -122,7 +122,12 @@ HB_Bool qShapeItem(HB_ShaperItem *item)
 
 HB_Face qHBNewFace(void *font, HB_GetFontTableFunc tableFunc)
 {
-    return HB_NewFace(font, tableFunc);
+    return HB_AllocFace(font, tableFunc);
+}
+
+HB_Face qHBLoadFace(HB_Face face)
+{
+    return HB_LoadFace(face);
 }
 
 void qHBFreeFace(HB_Face face)

src/corelib/tools/qharfbuzz_p.h

@@ -68,6 +68,7 @@ Q_CORE_EXPORT HB_Bool qShapeItem(HB_ShaperItem *item);
 // ### temporary
 Q_CORE_EXPORT HB_Face qHBNewFace(void *font, HB_GetFontTableFunc tableFunc);
 Q_CORE_EXPORT void qHBFreeFace(HB_Face);
+Q_CORE_EXPORT HB_Face qHBLoadFace(HB_Face face);
 
 Q_DECLARE_TYPEINFO(HB_GlyphAttributes, Q_PRIMITIVE_TYPE);
 Q_DECLARE_TYPEINFO(HB_FixedPoint, Q_PRIMITIVE_TYPE);

src/gui/text/qfontengine.cpp

@@ -227,6 +227,15 @@ HB_Face QFontEngine::harfbuzzFace() const
     return hbFace;
 }
 
+HB_Face QFontEngine::initializedHarfbuzzFace() const
+{
+    HB_Face face = harfbuzzFace();
+    if (face != 0 && face->font_for_init != 0)
+        face = qHBLoadFace(face);
+
+    return face;
+}
+
 glyph_metrics_t QFontEngine::boundingBox(glyph_t glyph, const QTransform &matrix)
 {
     glyph_metrics_t metrics = boundingBox(glyph);
@@ -1364,15 +1373,13 @@ bool QFontEngineMulti::stringToCMap(const QChar *str, int len,
         if (glyphs->glyphs[glyph_pos] == 0 && str[i].category() != QChar::Separator_Line) {
             QGlyphLayoutInstance tmp = glyphs->instance(glyph_pos);
             for (int x=1; x < engines.size(); ++x) {
-                if (!shouldLoadFontEngineForCharacter(x, ucs4))
+                if (engines.at(x) == 0 && !shouldLoadFontEngineForCharacter(x, ucs4))
                     continue;
 
                 QFontEngine *engine = engines.at(x);
-                bool deleteThisEngine = false;
                 if (!engine) {
                     const_cast<QFontEngineMulti *>(this)->loadEngine(x);
                     engine = engines.at(x);
-                    deleteThisEngine = true;
                 }
                 Q_ASSERT(engine != 0);
                 if (engine->type() == Box)
@@ -1388,8 +1395,6 @@ bool QFontEngineMulti::stringToCMap(const QChar *str, int len,
                     // set the high byte to indicate which engine the glyph came from
                     glyphs->glyphs[glyph_pos] |= (x << 24);
                     break;
-                } else if (deleteThisEngine) {
-                    const_cast<QFontEngineMulti *>(this)->unloadEngine(x);
                 }
             }
 

src/gui/text/qfontengine_p.h

@@ -235,6 +235,7 @@ public:
 
     HB_Font harfbuzzFont() const;
     HB_Face harfbuzzFace() const;
+    HB_Face initializedHarfbuzzFace() const;
 
     virtual HB_Error getPointInOutline(HB_Glyph glyph, int flags, hb_uint32 point, HB_Fixed *xpos, HB_Fixed *ypos, hb_uint32 *nPoints);
 

src/gui/text/qtextengine.cpp

@@ -1112,7 +1112,7 @@ void QTextEngine::shapeTextWithHarfbuzz(int item) const
         si.leading = qMax(actualFontEngine->leading(), si.leading);
 
         shaper_item.font = actualFontEngine->harfbuzzFont();
-        shaper_item.face = actualFontEngine->harfbuzzFace();
+        shaper_item.face = actualFontEngine->initializedHarfbuzzFace();
 
         shaper_item.glyphIndicesPresent = true;