Common Font Operations

This chapter describes some common font-handling operations and shows how to code them using Core Text. These operations are the same on iOS and OS X. The following operations with code listings are included in this chapter:

Creating Font Descriptors

The example function in Listing 3-1 creates a font descriptor from parameter values specifying a PostScript font name and the point size.

Listing 3-1  Creating a font descriptor from a name and point size

CTFontDescriptorRef CreateFontDescriptorFromName(CFStringRef postScriptName,
                                                  CGFloat size)
{
    return CTFontDescriptorCreateWithNameAndSize(postScriptName, size);
}

The example function in Listing 3-2 creates a font descriptor from a font family name and font traits.

Listing 3-2  Creating a font descriptor from a family and traits

NSString* familyName = @"Papyrus";
CTFontSymbolicTraits symbolicTraits = kCTFontTraitCondensed;
CGFloat size = 24.0;
 
NSMutableDictionary* attributes = [NSMutableDictionary dictionary];
[attributes setObject:familyName forKey:(id)kCTFontFamilyNameAttribute];
 
// The attributes dictionary contains another dictionary, the traits dictionary,
// which in this example specifies only the symbolic traits.
NSMutableDictionary* traits = [NSMutableDictionary dictionary];
[traits setObject:[NSNumber numberWithUnsignedInt:symbolicTraits]
                                           forKey:(id)kCTFontSymbolicTrait];
 
[attributes setObject:traits forKey:(id)kCTFontTraitsAttribute];
[attributes setObject:[NSNumber numberWithFloat:size]
                                         forKey:(id)kCTFontSizeAttribute];
 
CTFontDescriptorRef descriptor =
             CTFontDescriptorCreateWithAttributes((CFDictionaryRef)attributes);
CFRelease(descriptor);

Creating a Font from a Font Descriptor

Listing 3-3 shows how to create a font descriptor and use it to create a font. When you call CTFontCreateWithFontDescriptor, you usually pass NULL for the matrix parameter to specify the default (identity) matrix. The size and matrix (second and third) parameters of CTFontCreateWithFontDescriptor override any specified in the font descriptor unless they are unspecified (0.0 for size and NULL for matrix).

Listing 3-3  Creating a font from a font descriptor

NSDictionary *fontAttributes =
                  [NSDictionary dictionaryWithObjectsAndKeys:
                          @"Courier", (NSString *)kCTFontFamilyNameAttribute,
                          @"Bold", (NSString *)kCTFontStyleNameAttribute,
                          [NSNumber numberWithFloat:16.0],
                          (NSString *)kCTFontSizeAttribute,
                          nil];
// Create a descriptor.
CTFontDescriptorRef descriptor =
          CTFontDescriptorCreateWithAttributes((CFDictionaryRef)fontAttributes);
 
// Create a font using the descriptor.
CTFontRef font = CTFontCreateWithFontDescriptor(descriptor, 0.0, NULL);
CFRelease(descriptor);

Creating Related Fonts

It is often useful to convert an existing font to a related or similar font. The example function in Listing 3-4 shows how to make a font bold or unbold based on the value of the Boolean parameter passed with the function call. If the current font family does not have the requested style, the function returns NULL.

Listing 3-4  Changing traits of a font

CTFontRef CreateBoldFont(CTFontRef font, Boolean makeBold)
{
    CTFontSymbolicTraits desiredTrait = 0;
    CTFontSymbolicTraits traitMask;
 
    // If requesting that the font be bold, set the desired trait
    // to be bold.
    if (makeBold) desiredTrait = kCTFontBoldTrait;
 
    // Mask off the bold trait to indicate that it is the only trait
    // to be modified. As CTFontSymbolicTraits is a bit field,
    // could change multiple traits if desired.
    traitMask = kCTFontBoldTrait;
 
    // Create a copy of the original font with the masked trait set to the
    // desired value. If the font family does not have the appropriate style,
    // returns NULL.
 
    return CTFontCreateCopyWithSymbolicTraits(font, 0.0, NULL, desiredTrait, traitMask);
}

The example function in Listing 3-8 converts a given font to a similar font in another font family, preserving traits if possible. It may return NULL. Passing in 0.0 for the size parameter and NULL for the matrix parameter preserves the size from the original font.

Listing 3-5  Converting a font to another family

CTFontRef CreateFontConvertedToFamily(CTFontRef font, CFStringRef family)
{
    // Create a copy of the original font with the new family. This call
    // attempts to preserve traits, and may return NULL if that is not possible.
    // Pass in 0.0 and NULL for size and matrix to preserve the values from
    // the original font.
 
    return CTFontCreateCopyWithFamily(font, 0.0, NULL, family);
}

Serializing a Font

The example function in Listing 3-6 shows how to create XML data to serialize a font that can be embedded in a document. Alternatively, and preferably, NSArchiver could be used. This is just one way to accomplish this task, but it preserves all data from the font needed to recreate the exact font at a later time.

Listing 3-6  Serializing a font

CFDataRef CreateFlattenedFontData(CTFontRef font)
{
    CFDataRef           result = NULL;
    CTFontDescriptorRef descriptor;
    CFDictionaryRef     attributes;
 
    // Get the font descriptor for the font.
    descriptor = CTFontCopyFontDescriptor(font);
 
    if (descriptor != NULL) {
        // Get the font attributes from the descriptor. This should be enough
        // information to recreate the descriptor and the font later.
        attributes = CTFontDescriptorCopyAttributes(descriptor);
 
        if (attributes != NULL) {
            // If attributes are a valid property list, directly flatten
            // the property list. Otherwise we may need to analyze the attributes
            // and remove or manually convert them to serializable forms.
            // This is left as an exercise for the reader.
           if (CFPropertyListIsValid(attributes, kCFPropertyListXMLFormat_v1_0)) {
                result = CFPropertyListCreateXMLData(kCFAllocatorDefault, attributes);
            }
        }
    }
    return result;
}

Creating a Font from Serialized Data

The example function in Listing 3-7 shows how to create a font reference from flattened XML data. It shows how to unflatten font attributes and create a font with those attributes.

Listing 3-7  Creating a font from serialized data

CTFontRef CreateFontFromFlattenedFontData(CFDataRef iData)
{
    CTFontRef           font = NULL;
    CFDictionaryRef     attributes;
    CTFontDescriptorRef descriptor;
 
    // Create our font attributes from the property list.
    // For simplicity, this example creates an immutable object.
    // If you needed to massage or convert certain attributes
    // from their serializable form to the Core Text usable form,
    // do it here.
    attributes =
          (CFDictionaryRef)CFPropertyListCreateFromXMLData(
                               kCFAllocatorDefault,
                               iData, kCFPropertyListImmutable, NULL);
    if (attributes != NULL) {
        // Create the font descriptor from the attributes.
        descriptor = CTFontDescriptorCreateWithAttributes(attributes);
        if (descriptor != NULL) {
            // Create the font from the font descriptor. This sample uses
            // 0.0 and NULL for the size and matrix parameters. This
            // causes the font to be created with the size and/or matrix
            // that exist in the descriptor, if present. Otherwise default
            // values are used.
            font = CTFontCreateWithFontDescriptor(descriptor, 0.0, NULL);
        }
    }
    return font;
}

Changing Kerning

Ligatures and kerning are enabled by default. To disable, set the kCTKernAttributeName attribute to 0. Listing 3-8 sets the kern size to a large number for the first few characters drawn.

Listing 3-8  Setting kerning

 // Set the color of the first 13 characters to red
 // using a previously defined red CGColor object.
 CFAttributedStringSetAttribute(attrString, CFRangeMake(0, 13),
                                      kCTForegroundColorAttributeName, red);
 
 // Set kerning between the first 18 chars to be 20
 CGFloat otherNum = 20;
 CFNumberRef otherCFNum = CFNumberCreate(NULL, kCFNumberCGFloatType, &otherNum);
 CFAttributedStringSetAttribute(attrString, CFRangeMake(0,18),
                                           kCTKernAttributeName, otherCFNum);

Getting Glyphs for Characters

Listing 3-9 shows how to get glyphs for the characters in a string with a single font. Most of the time you should just use a CTLine object to get this information because one font may not encode the entire string. In addition, simple character-to-glyph mapping will not get the correct appearance for complex scripts. This simple glyph mapping may be appropriate if you are trying to display specific Unicode characters for a font.

Listing 3-9  Getting glyphs for characters

void GetGlyphsForCharacters(CTFontRef font, CFStringRef string)
{
    // Get the string length.
    CFIndex count = CFStringGetLength(string);
 
    // Allocate our buffers for characters and glyphs.
    UniChar *characters = (UniChar *)malloc(sizeof(UniChar) * count);
    CGGlyph *glyphs = (CGGlyph *)malloc(sizeof(CGGlyph) * count);
 
    // Get the characters from the string.
    CFStringGetCharacters(string, CFRangeMake(0, count), characters);
 
    // Get the glyphs for the characters.
    CTFontGetGlyphsForCharacters(font, characters, glyphs, count);
 
    // Do something with the glyphs here. Characters not mapped by this font will be zero.
    // ...
 
    // Free the buffers
    free(characters);
    free(glyphs);
}


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