optimize QRawFont::supportsCharacter()

a single UCS-4-encoded codepoint could morph into 1 or 2 UCS-2-encoded codepoints only;
thus, allocating QString just to parse it could be avoided and the well-defined
UCS-4 to UCS-2 arithmetic could be used instead

Merge-request: 1305
Reviewed-by: Jiang Jiang <jiang.jiang@nokia.com>

2 files changed, 15 insertions, 4 deletions

diff --git a/src/gui/text/qrawfont.cpp b/src/gui/text/qrawfont.cpp
index 2c60b14..e3e5c57 100644
--- a/src/gui/text/qrawfont.cpp
+++ b/src/gui/text/qrawfont.cpp
@@ -624,7 +624,7 @@ QList<QFontDatabase::WritingSystem> QRawFont::supportedWritingSystems() const
 
     \sa supportedWritingSystems()
 */
-bool QRawFont::supportsCharacter(const QChar &character) const
+bool QRawFont::supportsCharacter(QChar character) const
 {
     if (!isValid())
         return false;
@@ -633,6 +633,7 @@ bool QRawFont::supportsCharacter(const QChar &character) const
 }
 
 /*!
+    \overload
    Returns true if the font has a glyph that corresponds to the UCS-4 encoded character \a ucs4.
 
    \sa supportedWritingSystems()
@@ -642,8 +643,18 @@ bool QRawFont::supportsCharacter(quint32 ucs4) const
     if (!isValid())
         return false;
 
-    QString str = QString::fromUcs4(&ucs4, 1);
-    return d->fontEngine->canRender(str.constData(), str.size());
+    QChar str[2];
+    int len;
+    if (!QChar::requiresSurrogates(ucs4)) {
+        str[0] = QChar(ucs4);
+        len = 1;
+    } else {
+        str[0] = QChar(QChar::highSurrogate(ucs4));
+        str[1] = QChar(QChar::lowSurrogate(ucs4));
+        len = 2;
+    }
+
+    return d->fontEngine->canRender(str, len);
 }
 
 // qfontdatabase.cpp
diff --git a/src/gui/text/qrawfont.h b/src/gui/text/qrawfont.h
index 88ec6cb..d5b5680 100644
--- a/src/gui/text/qrawfont.h
+++ b/src/gui/text/qrawfont.h
@@ -122,7 +122,7 @@ public:
                       QFont::HintingPreference hintingPreference);
 
     bool supportsCharacter(quint32 ucs4) const;
-    bool supportsCharacter(const QChar &character) const;
+    bool supportsCharacter(QChar character) const;
     QList<QFontDatabase::WritingSystem> supportedWritingSystems() const;
 
     QByteArray fontTable(const char *tagName) const;