Fix fontconfig usage in X11 font database

We should do FcConfigSubstitute(0, pattern, FcMatchFont) on a
FcPattern for query because the family list in it will contain
almost all the families after FcConfigSubstitute(0, pattern,
FcMatchPattern), then the test in <match target="font"> will
almost always succeed. In general, FcMatchFont substitute
should only be done on the FcPattern that we got after
FcFontMatch() or FcFontRenderPrepare().

Based on the suggestion of fontconfig author Behdad Esfahbod,
this patch reorganized the tryPatternLoad logic so that it only
does the QFontEngine creation part, FcPattern *match is retrieved
outside of that function. In this way, the match pattern we got
can be either from FcFontMatch() or after FcFontRenderPrepare()
on one of the fonts we got from qt_fontSetForPattern(). Then we
don't need to duplicate the pattern and add all criterias back
with qt_addPatternProps(). It not only simplified the code a lot
but also fix the way we apply FcMatchFont substitution. This
substitution will either be done by FcFontMatch() or
FcFontRenderPrepare, both implicitly.

Task-number: QTBUG-2148, QTBUG-19947
Reviewed-by: Eskil

2 files changed, 30 insertions, 48 deletions

diff --git a/src/gui/text/qfontdatabase_x11.cpp b/src/gui/text/qfontdatabase_x11.cpp
index 754334c..958daa2 100644
--- a/src/gui/text/qfontdatabase_x11.cpp
+++ b/src/gui/text/qfontdatabase_x11.cpp
@@ -1566,9 +1566,8 @@ static FcPattern *getFcPattern(const QFontPrivate *fp, int script, const QFontDe
 
     qt_addPatternProps(pattern, fp->screen, script, request);
 
-    FcDefaultSubstitute(pattern);
     FcConfigSubstitute(0, pattern, FcMatchPattern);
-    FcConfigSubstitute(0, pattern, FcMatchFont);
+    FcDefaultSubstitute(pattern);
 
     // these should only get added to the pattern _after_ substitution
     // append the default fallback font for the specified script
@@ -1606,35 +1605,20 @@ static void FcFontSetRemove(FcFontSet *fs, int at)
         memmove(fs->fonts + at, fs->fonts + at + 1, len);
 }
 
-static QFontEngine *tryPatternLoad(FcPattern *p, int screen,
-                                   const QFontDef &request, int script, FcPattern **matchedPattern = 0)
+static QFontEngine *tryPatternLoad(FcPattern *match, int screen,
+                                   const QFontDef &request, int script)
 {
 #ifdef FONT_MATCH_DEBUG
     FcChar8 *fam;
-    FcPatternGetString(p, FC_FAMILY, 0, &fam);
+    FcPatternGetString(match, FC_FAMILY, 0, &fam);
     FM_DEBUG("==== trying %s\n", fam);
 #endif
     FM_DEBUG("passes charset test\n");
-    FcPattern *pattern = FcPatternDuplicate(p);
-    // add properties back in as the font selected from the
-    // list doesn't contain them.
-    qt_addPatternProps(pattern, screen, script, request);
-
-    FcConfigSubstitute(0, pattern, FcMatchPattern);
-    FcDefaultSubstitute(pattern);
-    FcResult res;
-    FcPattern *match = FcFontMatch(0, pattern, &res);
-
-    if (matchedPattern)
-	*matchedPattern = 0;
 
     QFontEngineX11FT *engine = 0;
     if (!match) // probably no fonts available.
         goto done;
 
-    if (matchedPattern)
-	*matchedPattern = FcPatternDuplicate(match);
-
     if (script != QUnicodeTables::Common) {
         // skip font if it doesn't support the language we want
         if (specialChars[script]) {
@@ -1673,11 +1657,6 @@ static QFontEngine *tryPatternLoad(FcPattern *p, int screen,
         }
     }
 done:
-    FcPatternDestroy(pattern);
-    if (!engine && matchedPattern && *matchedPattern) {
-        FcPatternDestroy(*matchedPattern);
-        *matchedPattern = 0;
-    }
     return engine;
 }
 
@@ -1726,14 +1705,26 @@ static QFontEngine *loadFc(const QFontPrivate *fp, int script, const QFontDef &r
 #endif
 
     QFontEngine *fe = 0;
-    FcPattern *matchedPattern = 0;
-    fe = tryPatternLoad(pattern, fp->screen, request, script, &matchedPattern);
+    FcResult res;
+    FcPattern *match = FcFontMatch(0, pattern, &res);
+    fe = tryPatternLoad(match, fp->screen, request, script);
     if (!fe) {
         FcFontSet *fs = qt_fontSetForPattern(pattern, request);
 
+        if (match) {
+            FcPatternDestroy(match);
+            match = 0;
+        }
+
         if (fs) {
-            for (int i = 0; !fe && i < fs->nfont; ++i)
-                fe = tryPatternLoad(fs->fonts[i], fp->screen, request, script, &matchedPattern);
+            for (int i = 0; !fe && i < fs->nfont; ++i) {
+                match = FcFontRenderPrepare(NULL, pattern, fs->fonts[i]);
+                fe = tryPatternLoad(match, fp->screen, request, script);
+                if (fe)
+                    break;
+                FcPatternDestroy(match);
+                match = 0;
+            }
             FcFontSetDestroy(fs);
         }
         FM_DEBUG("engine for script %d is %s\n", script, fe ? fe->fontDef.family.toLatin1().data(): "(null)");
@@ -1741,11 +1732,11 @@ static QFontEngine *loadFc(const QFontPrivate *fp, int script, const QFontDef &r
     if (fe
         && script == QUnicodeTables::Common
         && !(request.styleStrategy & QFont::NoFontMerging) && !fe->symbol) {
-        fe = new QFontEngineMultiFT(fe, matchedPattern, pattern, fp->screen, request);
+        fe = new QFontEngineMultiFT(fe, match, pattern, fp->screen, request);
     } else {
         FcPatternDestroy(pattern);
-        if (matchedPattern)
-            FcPatternDestroy(matchedPattern);
+        if (match)
+            FcPatternDestroy(match);
     }
     return fe;
 }
diff --git a/src/gui/text/qfontengine_x11.cpp b/src/gui/text/qfontengine_x11.cpp
index e3bfa5d..c4ed0ca 100644
--- a/src/gui/text/qfontengine_x11.cpp
+++ b/src/gui/text/qfontengine_x11.cpp
@@ -863,11 +863,8 @@ glyph_t QFontEngineXLFD::glyphIndexToFreetypeGlyphIndex(glyph_t g) const
 // Multi FT engine
 // ------------------------------------------------------------------
 
-static QFontEngine *engineForPattern(FcPattern *pattern, const QFontDef &request,
-                                     int screen)
+static QFontEngine *engineForPattern(FcPattern *match, const QFontDef &request, int screen)
 {
-    FcResult res;
-    FcPattern *match = FcFontMatch(0, pattern, &res);
     QFontEngineX11FT *engine = new QFontEngineX11FT(match, request, screen);
     if (!engine->invalid())
         return engine;
@@ -879,9 +876,9 @@ static QFontEngine *engineForPattern(FcPattern *pattern, const QFontDef &request
 }
 
 QFontEngineMultiFT::QFontEngineMultiFT(QFontEngine *fe, FcPattern *matchedPattern, FcPattern *p, int s, const QFontDef &req)
-    : QFontEngineMulti(2), request(req), pattern(p), firstEnginePattern(matchedPattern), fontSet(0), screen(s)
+    : QFontEngineMulti(2), request(req), pattern(p), fontSet(0), screen(s)
 {
-
+    firstEnginePattern = FcPatternDuplicate(matchedPattern);
     engines[0] = fe;
     engines.at(0)->ref.ref();
     fontDef = engines[0]->fontDef;
@@ -907,8 +904,6 @@ void QFontEngineMultiFT::loadEngine(int at)
     extern QMutex *qt_fontdatabase_mutex();
     QMutexLocker locker(qt_fontdatabase_mutex());
 
-    extern void qt_addPatternProps(FcPattern *pattern, int screen, int script,
-                                   const QFontDef &request);
     extern QFontDef qt_FcPatternToQFontDef(FcPattern *pattern, const QFontDef &);
     extern FcFontSet *qt_fontSetForPattern(FcPattern *pattern, const QFontDef &request);
 
@@ -940,22 +935,18 @@ void QFontEngineMultiFT::loadEngine(int at)
     Q_ASSERT(at < engines.size());
     Q_ASSERT(engines.at(at) == 0);
 
-    FcPattern *pattern = FcPatternDuplicate(fontSet->fonts[at + firstFontIndex - 1]);
-    qt_addPatternProps(pattern, screen, QUnicodeTables::Common, request);
-
-    QFontDef fontDef = qt_FcPatternToQFontDef(pattern, this->request);
+    FcPattern *match = FcFontRenderPrepare(NULL, pattern, fontSet->fonts[at + firstFontIndex - 1]);
+    QFontDef fontDef = qt_FcPatternToQFontDef(match, this->request);
 
     // note: we use -1 for the script to make sure that we keep real
     // FT engines separate from Multi engines in the font cache
     QFontCache::Key key(fontDef, -1, screen);
     QFontEngine *fontEngine = QFontCache::instance()->findEngine(key);
     if (!fontEngine) {
-        FcConfigSubstitute(0, pattern, FcMatchPattern);
-        FcDefaultSubstitute(pattern);
-        fontEngine = engineForPattern(pattern, request, screen);
+        fontEngine = engineForPattern(match, request, screen);
         QFontCache::instance()->insertEngine(key, fontEngine);
     }
-    FcPatternDestroy(pattern);
+    FcPatternDestroy(match);
     fontEngine->ref.ref();
     engines[at] = fontEngine;
 }