Objective-C - CTFont change font style?

问题

I have a CTFont that contains a font style, and sumbolic traits.

I want to create a new font with a new style that inherits the symbolic traits of the first font. How can I achieve this?

CTFontRef newFontWithoutTraits = CTFontCreateWithName((CFString)newFontName, CTFontGetSize(font), NULL);
CTFontRef newFont = CTFontCreateCopyWithSymbolicTraits(newFontWithoutTraits, CTFontGetSize(font), NULL, 0, CTFontGetSymbolicTraits(font));

the new font is null here I don't know what should I pass to the 4th parameter in CTFontCreateCopyWithSymbolicTraits.

回答1:

I do this line of code to generate a bold font from non-bold font:

CTFontRef newFont = CTFontCreateCopyWithSymbolicTraits(currentFont, 0.0, NULL, (wantBold?kCTFontBoldTrait:0), kCTFontBoldTrait);

• currentFont is the CTFontRef I want to add symbolic traits to
• wantBold is a boolean to tell if I want to add or remove the bold trait to the font
• kCTFontBoldTrait is the symbolic trait I want to modify on the font.

The 4th parameter is the value you want to apply. The 5th is the mask to select the symbolic trait.

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You may thing of it as bitmask to apply to the symbolic trait, where the 4th parameter of CTFontCreateCopyWithSymbolicTraits is the value and the 5th parameter is the mask:

• If you want to set the symtrait and add it to the font, iOS will probably apply sthg like newTrait = oldTrait | (value&mask), setting the bit corresponding to mask to the value of value.

• If you want to unset the symtrait and remove it from the font, you use the value of 0 as the 4th parameter and iOS will probably apply sthg like newTrait = oldTrait & ~mask to unset the bit.

• But if you need to, you can also set and unset multiple bits (thus multiple symbolic traits) at once, using the right value that have 1 on bits to set and 0 on bits to unset (or to ignore), and and using the right mask that have 1 on bits that needs to be modified and 0 on bits that don't need to be changed.

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[EDIT2]

I finally managed to find the solution for your specific case: you need to get the symtraits mask of your font as you already do… and bitwise-or it with the symtraits of your newFontWithoutTraits font.

This is because newFontWithoutTraits actually do have default symtraits (contrary to what I thought, it has a non-zero CTFontSymbolicTraits value) as the symtraits value also contains info for the font class and such things (so even a non-bold, non-italic font can have a non-zero symtraits value, log the hex value of the symtraits of your font to understand better).

So this is the code you need:

CTFontRef font = CTFontCreateWithName((CFStringRef)@"Courier Bold", 12, NULL);
CGFloat fontSize = CTFontGetSize(font);
CTFontSymbolicTraits fontTraits = CTFontGetSymbolicTraits(font);
CTFontRef newFontWithoutTraits = CTFontCreateWithName((CFStringRef)@"Arial", fontSize, NULL);
fontTraits |= CTFontGetSymbolicTraits(newFontWithoutTraits);
CTFontRef newFont = CTFontCreateCopyWithSymbolicTraits(newFontWithoutTraits, fontSize, NULL, fontTraits, fontTraits);

// Check the results (yes, this NSLog create leaks as I don't release the CFStrings, but this is just for debugging)
NSLog(@"font:%@, newFontWithoutTraits:%@, newFont:%@", CTFontCopyFullName(font), CTFontCopyFullName(newFontWithoutTraits), CTFontCopyFullName(newFont));

// Clear memory (CoreFoundation "Create Rule", objects needs to be CFRelease'd)
CFRelease(newFont);
CFRelease(newFontWithoutTraits);
CFRelease(font);

来源：https://stackoverflow.com/questions/7492237/objective-c-ctfont-change-font-style