Add some QRawFont related low level functions to avoid extra copying

Added functions:

- QRawFont::glyphIndexesForChars(const QChar *chars, int numChars,
  quint32 *glyphIndexes, int *numGlyphs) const
- QRawFont::advancesForGlyphIndexes(const quint32 *glyphIndexes,
  QPointF *advances, int numGlyphs) const

Reviewed-by: Eskil
(cherry picked from commit 965af9eb2932efae5d736df54c3859460017b6a5)

src/gui/text/qrawfont.cpp

@@ -428,7 +428,7 @@ int QRawFont::weight() const
    of the text. To get the correctly shaped text, you can use QTextLayout to lay out and shape the
    text, and then call QTextLayout::glyphRuns() to get the set of glyph index list and QRawFont pairs.
 
-   \sa advancesForGlyphIndexes(), QGlyphRun, QTextLayout::glyphRuns(), QTextFragment::glyphRuns()
+   \sa advancesForGlyphIndexes(), glyphIndexesForChars(), QGlyphRun, QTextLayout::glyphRuns(), QTextFragment::glyphRuns()
 */
 QVector<quint32> QRawFont::glyphIndexesForString(const QString &text) const
 {
@@ -437,11 +437,9 @@ QVector<quint32> QRawFont::glyphIndexesForString(const QString &text) const
 
     int nglyphs = text.size();
     QVarLengthGlyphLayoutArray glyphs(nglyphs);
-    if (!d->fontEngine->stringToCMap(text.data(), text.size(), &glyphs, &nglyphs,
-                                  QTextEngine::GlyphIndicesOnly)) {
+    if (!glyphIndexesForChars(text.data(), text.size(), glyphs.glyphs, &nglyphs)) {
         glyphs.resize(nglyphs);
-        if (!d->fontEngine->stringToCMap(text.data(), text.size(), &glyphs, &nglyphs,
-                                      QTextEngine::GlyphIndicesOnly)) {
+        if (!glyphIndexesForChars(text.data(), text.size(), glyphs.glyphs, &nglyphs)) {
             Q_ASSERT_X(false, Q_FUNC_INFO, "stringToCMap shouldn't fail twice");
             return QVector<quint32>();
         }
@@ -454,6 +452,26 @@ QVector<quint32> QRawFont::glyphIndexesForString(const QString &text) const
     return glyphIndexes;
 }
 
+/*!
+   Converts a string of unicode points to glyph indexes using the CMAP table in the
+   underlying font. The function works like glyphIndexesForString() except it take
+   an array (\a chars), the results will be returned though \a glyphIndexes array
+   and number of glyphs will be set in \a numGlyphs. The size of \a glyphIndexes array
+   must be at least \a numChars, if that's still not enough, this function will return
+   false, then you can resize \a glyphIndexes from the size returned in \a numGlyphs.
+
+   \sa glyphIndexesForString(), advancesForGlyphIndexes(), QGlyphs, QTextLayout::glyphs(), QTextFragment::glyphs()
+*/
+bool QRawFont::glyphIndexesForChars(const QChar *chars, int numChars, quint32 *glyphIndexes, int *numGlyphs) const
+{
+    if (!isValid())
+        return false;
+
+    QGlyphLayout glyphs;
+    glyphs.glyphs = glyphIndexes;
+    return d->fontEngine->stringToCMap(chars, numChars, &glyphs, numGlyphs, QTextEngine::GlyphIndicesOnly);
+}
+
 /*!
    Returns the QRawFont's advances for each of the \a glyphIndexes in pixel units. The advances
    give the distance from the position of a given glyph to where the next glyph should be drawn
@@ -479,6 +497,36 @@ QVector<QPointF> QRawFont::advancesForGlyphIndexes(const QVector<quint32> &glyph
     return advances;
 }
 
+/*!
+   Returns the QRawFont's advances for each of the \a glyphIndexes in pixel units. The advances
+   give the distance from the position of a given glyph to where the next glyph should be drawn
+   to make it appear as if the two glyphs are unspaced. The glyph indexes are given with the
+   array \a glyphIndexes while the results are returned through \a advances, both of them must
+   have \a numGlyphs elements.
+
+   \sa QTextLine::horizontalAdvance(), QFontMetricsF::width()
+*/
+bool QRawFont::advancesForGlyphIndexes(const quint32 *glyphIndexes, QPointF *advances, int numGlyphs) const
+{
+    if (!isValid())
+        return false;
+
+    QGlyphLayout glyphs;
+    glyphs.glyphs = const_cast<HB_Glyph *>(glyphIndexes);
+    glyphs.numGlyphs = numGlyphs;
+    QVarLengthArray<QFixed> advances_x(numGlyphs);
+    QVarLengthArray<QFixed> advances_y(numGlyphs);
+    glyphs.advances_x = advances_x.data();
+    glyphs.advances_y = advances_y.data();
+
+    d->fontEngine->recalcAdvances(&glyphs, 0);
+
+    for (int i=0; i<numGlyphs; ++i)
+        advances[i] = QPointF(glyphs.advances_x[i].toReal(), glyphs.advances_y[i].toReal());
+
+    return true;
+}
+
 /*!
    Returns the hinting preference used to construct this QRawFont.
 

src/gui/text/qrawfont.h

@@ -90,6 +90,8 @@ public:
 
     QVector<quint32> glyphIndexesForString(const QString &text) const;
     QVector<QPointF> advancesForGlyphIndexes(const QVector<quint32> &glyphIndexes) const;
+    bool glyphIndexesForChars(const QChar *chars, int numChars, quint32 *glyphIndexes, int *numGlyphs) const;
+    bool advancesForGlyphIndexes(const quint32 *glyphIndexes, QPointF *advances, int numGlyphs) const;
 
     QImage alphaMapForGlyph(quint32 glyphIndex,
                             AntialiasingType antialiasingType = SubPixelAntialiasing,