[QFontEngineBox] Fix incorrect advances for SMP code points

In UTF-16, SMP code point is encoded with a pair of surrogates,
thus making SMP code point twice wider than BMP code point.

Change-Id: Ifb0e78cff50cca7231d07097a730188bd98c54cb
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/gui/text/qfontengine.cpp b/src/gui/text/qfontengine.cpp
index 7dfd9423e9..a3fce197ce 100644
--- a/src/gui/text/qfontengine.cpp
+++ b/src/gui/text/qfontengine.cpp
@@ -1299,17 +1299,24 @@ QFontEngineBox::~QFontEngineBox()
 {
 }
 
-bool QFontEngineBox::stringToCMap(const QChar *, int len, QGlyphLayout *glyphs, int *nglyphs, QFontEngine::ShaperFlags flags) const
+bool QFontEngineBox::stringToCMap(const QChar *str, int len, QGlyphLayout *glyphs, int *nglyphs, QFontEngine::ShaperFlags flags) const
 {
     if (*nglyphs < len) {
         *nglyphs = len;
         return false;
     }
 
-    memset(glyphs->glyphs, 0, len * sizeof(glyph_t));
+    int ucs4Length = 0;
+    for (int i = 0; i < len; ++i) {
+        if (str[i].isHighSurrogate() && i + 1 < len && str[i + 1].isLowSurrogate())
+            ++ucs4Length;
+        ++ucs4Length;
+    }
+
+    memset(glyphs->glyphs, 0, ucs4Length * sizeof(glyph_t));
 
-    *nglyphs = len;
-    glyphs->numGlyphs = len;
+    *nglyphs = ucs4Length;
+    glyphs->numGlyphs = ucs4Length;
 
     if (!(flags & GlyphIndicesOnly))
         recalcAdvances(glyphs, flags);