Workaround a bug in Core Text to select Light fonts

Currently in Core Text there is not proper way to select fonts with
Light weight, for example:
QFont font("Helvetica"); font.setWeight(QFont::Light);
will give you Helvetica-Light, as with:
QFont font("Helvetica"); font.setWeight(QFont::Normal);
because of a bug in Core Text, applying 0 symbolic traits with
CTFontCreateCopyWithSymbolicTraits will always return the Light
variant of that font family. Thus, we should only do this unless
symbolicTraits is not 0 or font.weight is not Normal (Light is not
a symbolic trait, but CT doesn't support selecting Light weight
numerically).

Reviewed-by: Eskil
(cherry picked from commit 4d5b8f66d82e9087d9d58a4e76e6b46ce7bb53cc)

Change-Id: I37a970aba5019a13b9f3bc43b7fb594b74a1aa37
Reviewed-on: http://codereview.qt.nokia.com/124
Reviewed-by: Jiang Jiang <jiang.jiang@nokia.com>

diff --git a/src/gui/text/qfontengine_coretext.mm b/src/gui/text/qfontengine_coretext.mm
index 24bd750..737edc3 100644 (file)
--- a/src/gui/text/qfontengine_coretext.mm
+++ b/src/gui/text/qfontengine_coretext.mm
@@ -100,7 +100,12 @@ QCoreTextFontEngineMulti::QCoreTextFontEngineMulti(const QCFString &name, const
 
     QCFType<CTFontDescriptorRef> descriptor = CTFontDescriptorCreateWithNameAndSize(name, fontDef.pixelSize);
     QCFType<CTFontRef> baseFont = CTFontCreateWithFontDescriptor(descriptor, fontDef.pixelSize, &transform);
-    ctfont = CTFontCreateCopyWithSymbolicTraits(baseFont, fontDef.pixelSize, &transform, symbolicTraits, symbolicTraits);
+    ctfont = NULL;
+    // There is a side effect in Core Text: if we apply 0 as symbolic traits to a font in normal weight,
+    // we will get the light version of that font (while the way supposed to work doesn't:
+    // setting kCTFontWeightTrait to some value between -1.0 to 0.0 has no effect on font selection)
+    if (fontDef.weight != QFont::Normal || symbolicTraits)
+        ctfont = CTFontCreateCopyWithSymbolicTraits(baseFont, fontDef.pixelSize, &transform, symbolicTraits, symbolicTraits);
 
     // CTFontCreateCopyWithSymbolicTraits returns NULL if we ask for a trait that does
     // not exist for the given font. (for example italic)