QFontMetrics/QRawFont: Optimize SMP code points handling a bit

Calling QString::fromUcs4() for the single UCS-4 -encoded character is quite suboptimal
since the BOM detections and the resulting QString aren't really used;
all we need is to split the UCS-4 code point into the UCS-2 surrogate pair.

Change-Id: Ia5b68312909bf551cf2493d9e2752a7d7d837fb9
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/gui/text/qfontengine_p.h b/src/gui/text/qfontengine_p.h
index 4741de3000..bcf763d5d9 100644
--- a/src/gui/text/qfontengine_p.h
+++ b/src/gui/text/qfontengine_p.h
@@ -225,6 +225,18 @@ public:
     virtual const char *name() const = 0;
 
     virtual bool canRender(const QChar *string, int len) = 0;
+    inline bool canRender(uint ucs4) {
+        QChar utf16[2];
+        int utf16len = 1;
+        if (QChar::requiresSurrogates(ucs4)) {
+            utf16[0] = QChar::highSurrogate(ucs4);
+            utf16[1] = QChar::lowSurrogate(ucs4);
+            ++utf16len;
+        } else {
+            utf16[0] = QChar(ucs4);
+        }
+        return canRender(utf16, utf16len);
+    }
 
     virtual Type type() const = 0;