Core Text框架详细解析（四） —— Core Text文本布局操作

版本记录

版本号	时间
V1.0	2017.10.22

前言

Core Text框架主要用来做文字处理，是的iOS3.2+和OSX10.5+中的文本引擎，让您精细的控制文本布局和格式。它位于在UIKit中和CoreGraphics/Quartz之间的最佳点。接下来这几篇我们就主要解析该框架。感兴趣的可以前面几篇。
1. Core Text框架详细解析（一） —— 基本概览
2. Core Text框架详细解析（二） —— 关于Core Text
3. Core Text框架详细解析（三） —— Core Text总体概览

字体布局操作

本章介绍一些常见的文本布局操作，并显示如何使用Core Text执行它们。 本章包含以下代码列表操作：

• Laying Out a Paragraph
• Simple Text Label
• Columnar Layout
• Manual Line Breaking
• Applying a Paragraph Style
• Displaying Text in a Nonrectangular Region

---

Laying Out a Paragraph - 布局一个段落

排版typesetting中最常见的操作之一是在任意大小的矩形区域内布置多行段落。 Core Text使此操作变得容易，只需要几行Core Text特定的代码。 要布置该段落，您需要绘制图形上下文，一个矩形路径来提供文本布局的区域，以及一个属性字符串。 此示例中的大多数代码是创建和初始化上下文，路径和字符串。 完成之后，Core Text只需要三行代码来进行布局。

Listing 2-1中的代码显示了段落的布局方式。 该代码可以驻留在UIView子类（OS X中的NSView子类）的drawRect:方法中。

// Listing 2-1  Typesetting a simple paragraph

// Initialize a graphics context in iOS.

CGContextRef context = UIGraphicsGetCurrentContext();
 
// Flip the context coordinates, in iOS only.
CGContextTranslateCTM(context, 0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
 
// Initializing a graphic context in OS X is different:
// CGContextRef context =
//     (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
 
// Set the text matrix.
CGContextSetTextMatrix(context, CGAffineTransformIdentity);
 
// Create a path which bounds the area where you will be drawing text.
// The path need not be rectangular.
CGMutablePathRef path = CGPathCreateMutable();
 
// In this simple example, initialize a rectangular path.
CGRect bounds = CGRectMake(10.0, 10.0, 200.0, 200.0);
CGPathAddRect(path, NULL, bounds );
 
// Initialize a string.
CFStringRef textString = CFSTR("Hello, World! I know nothing in the world that has as much power as a word. Sometimes I write one, and I look at it, until it begins to shine.");
 
// Create a mutable attributed string with a max length of 0.
// The max length is a hint as to how much internal storage to reserve.
// 0 means no hint.
CFMutableAttributedStringRef attrString =
         CFAttributedStringCreateMutable(kCFAllocatorDefault, 0);
 
// Copy the textString into the newly created attrString
CFAttributedStringReplaceString (attrString, CFRangeMake(0, 0),
         textString);
 
// Create a color that will be added as an attribute to the attrString.
CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = { 1.0, 0.0, 0.0, 0.8 };
CGColorRef red = CGColorCreate(rgbColorSpace, components);
CGColorSpaceRelease(rgbColorSpace);
 
// Set the color of the first 12 chars to red.
CFAttributedStringSetAttribute(attrString, CFRangeMake(0, 12),
         kCTForegroundColorAttributeName, red);
 
// Create the framesetter with the attributed string.
CTFramesetterRef framesetter =
         CTFramesetterCreateWithAttributedString(attrString);
CFRelease(attrString);
 
// Create a frame.
CTFrameRef frame = CTFramesetterCreateFrame(framesetter,
          CFRangeMake(0, 0), path, NULL);
 
// Draw the specified frame in the given context.
CTFrameDraw(frame, context);
 
// Release the objects we used.
CFRelease(frame);
CFRelease(path);
CFRelease(framesetter);

---

Simple Text Label - 简单文本标签

另一个常见的排版typesetting操作是绘制一行文本以用作用户界面Label的文本。 在Core Text中，这只需要两行代码：一个用CFAttributedString创建行对象，另一个用于将该行绘制到图形上下文中。

Listing 2-2 显示了如何在UIView或NSView子类的drawRect:方法中完成此操作。 该列表省略了在本文档中其他列表中显示的纯文本字符串，字体、图形上下文和操作的初始化。 它显示如何创建属性字典并使用它来创建属性字符串。 （字体创建显示在 Creating Font Descriptors 和 Creating a Font from a Font Descriptor。）

// Listing 2-2  Typesetting a simple text label

CFStringRef string; CTFontRef font; CGContextRef context;

// Initialize the string, font, and context
 
CFStringRef keys[] = { kCTFontAttributeName };
CFTypeRef values[] = { font };
 
CFDictionaryRef attributes =
    CFDictionaryCreate(kCFAllocatorDefault, (const void**)&keys,
        (const void**)&values, sizeof(keys) / sizeof(keys[0]),
        &kCFTypeDictionaryKeyCallBacks,
        &kCFTypeDictionaryValueCallBacks);
 
CFAttributedStringRef attrString =
    CFAttributedStringCreate(kCFAllocatorDefault, string, attributes);
CFRelease(string);
CFRelease(attributes);
 
CTLineRef line = CTLineCreateWithAttributedString(attrString);
 
// Set text position and draw the line into the graphics context
CGContextSetTextPosition(context, 10.0, 10.0);
CTLineDraw(line, context);
CFRelease(line);

---

Columnar Layout - 柱状布局

在多列中布局文本是另一种常见的排版typesetting操作。严格来说，Core Text本身一次只列出一列，不计算列大小或位置。您可以在调用Core Text之前进行这些操作，以便在您计算的路径区域中布置文本。在此示例中，Core Text除了在每列中布置文本之外，还为每列提供了文本字符串中的子范围。

Listing 2-3 中的createColumnsWithColumnCount:方法接受要绘制的列数的参数，并返回一个路径数组，每列的一个路径。

Listing 2-4 包括drawRect:方法的一个实现，它调用本列表中首先定义的本地createColumnsWithColumnCount方法。该代码驻留在UIView子类（OS X中的NSView子类）中。该子类包含一个attributString属性，此属性在此处未显示，但在此列表中调用其访问器以返回要排列的属性字符串。

// Listing 2-3  Dividing a view into columns

- (CFArrayRef)createColumnsWithColumnCount:(int)columnCount
{
    int column;
 
    CGRect* columnRects = (CGRect*)calloc(columnCount, sizeof(*columnRects));
    // Set the first column to cover the entire view.
    columnRects[0] = self.bounds;
 
    // Divide the columns equally across the frame's width.
    CGFloat columnWidth = CGRectGetWidth(self.bounds) / columnCount;
    for (column = 0; column < columnCount - 1; column++) {
        CGRectDivide(columnRects[column], &columnRects[column],
                     &columnRects[column + 1], columnWidth, CGRectMinXEdge);
    }
 
   // Inset all columns by a few pixels of margin.
    for (column = 0; column < columnCount; column++) {
        columnRects[column] = CGRectInset(columnRects[column], 8.0, 15.0);
    }
 
    // Create an array of layout paths, one for each column.
    CFMutableArrayRef array =
                     CFArrayCreateMutable(kCFAllocatorDefault,
                                  columnCount, &kCFTypeArrayCallBacks);
 
    for (column = 0; column < columnCount; column++) {
        CGMutablePathRef path = CGPathCreateMutable();
        CGPathAddRect(path, NULL, columnRects[column]);
        CFArrayInsertValueAtIndex(array, column, path);
        CFRelease(path);
    }
    free(columnRects);
    return array;
}

// Listing 2-4  Performing columnar text layout

// Override drawRect: to draw the attributed string into columns.
// (In OS X, the drawRect: method of NSView takes an NSRect parameter,
//  but that parameter is not used in this listing.)
- (void)drawRect:(CGRect)rect
{
    // Initialize a graphics context in iOS.
    CGContextRef context = UIGraphicsGetCurrentContext();
 
    // Flip the context coordinates in iOS only.
    CGContextTranslateCTM(context, 0, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
 
    // Initializing a graphic context in OS X is different:
    // CGContextRef context =
    //     (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
 
    // Set the text matrix.
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
 
    // Create the framesetter with the attributed string.
    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(
                                      (CFAttributedStringRef)self.attributedString);
 
    // Call createColumnsWithColumnCount function to create an array of
    // three paths (columns).
    CFArrayRef columnPaths = [self createColumnsWithColumnCount:3];
 
    CFIndex pathCount = CFArrayGetCount(columnPaths);
    CFIndex startIndex = 0;
    int column;
 
    // Create a frame for each column (path).
    for (column = 0; column < pathCount; column++) {
        // Get the path for this column.
        CGPathRef path = (CGPathRef)CFArrayGetValueAtIndex(columnPaths, column);
 
        // Create a frame for this column and draw it.
        CTFrameRef frame = CTFramesetterCreateFrame(
                             framesetter, CFRangeMake(startIndex, 0), path, NULL);
        CTFrameDraw(frame, context);
 
        // Start the next frame at the first character not visible in this frame.
        CFRange frameRange = CTFrameGetVisibleStringRange(frame);
        startIndex += frameRange.length;
        CFRelease(frame);
 
    }
    CFRelease(columnPaths);
    CFRelease(framesetter);
 
}

---

Manual Line Breaking - 手动换行

在Core Text中，您通常不需要进行手动换行，除非您有特殊的连字过程或类似的要求。 Framesetter会自动执行换行。 或者，Core Text使您能够准确地指定每行文本中断的位置。 Listing 2-5显示了如何创建一个排版机typesetter，一个由framesetter使用的对象，并直接使用排版机来找到适当的换行符并手动创建一个排版行。 此示例还显示了绘制之前如何居中的一行。

该代码可以在UIView子类的drawRect:方法（OS X中的NSView子类）中。 列表不显示代码中使用的变量的初始化。

// Listing 2-5  Performing manual line breaking

double width; CGContextRef context; CGPoint textPosition; CFAttributedStringRef attrString;
// Initialize those variables.
 
// Create a typesetter using the attributed string.
CTTypesetterRef typesetter = CTTypesetterCreateWithAttributedString(attrString);
 
// Find a break for line from the beginning of the string to the given width.
CFIndex start = 0;
CFIndex count = CTTypesetterSuggestLineBreak(typesetter, start, width);
 
// Use the returned character count (to the break) to create the line.
CTLineRef line = CTTypesetterCreateLine(typesetter, CFRangeMake(start, count));
 
// Get the offset needed to center the line.
float flush = 0.5; // centered
double penOffset = CTLineGetPenOffsetForFlush(line, flush, width);
 
// Move the given text drawing position by the calculated offset and draw the line.
CGContextSetTextPosition(context, textPosition.x + penOffset, textPosition.y);
CTLineDraw(line, context);
 
// Move the index beyond the line break.
start += count;

---

Applying a Paragraph Style - 应用段落样式

Listing 2-6实现了一个将段落样式应用于属性符串的函数。 该函数接受字体名称，点大小和增加或减少文本行之间的空格量的行间距的参数。 该函数由Listing 2-7中的代码调用，它创建一个纯文本字符串，使用applyParaStyle函数创建一个带有给定段落属性的属性字符串，然后创建一个framesetter 和frame，并绘制frame。

// Listing 2-6  Applying a paragraph style

NSAttributedString* applyParaStyle(
                CFStringRef fontName , CGFloat pointSize,
                NSString *plainText, CGFloat lineSpaceInc){
 
    // Create the font so we can determine its height.
    CTFontRef font = CTFontCreateWithName(fontName, pointSize, NULL);
 
    // Set the lineSpacing.
    CGFloat lineSpacing = (CTFontGetLeading(font) + lineSpaceInc) * 2;
 
    // Create the paragraph style settings.
    CTParagraphStyleSetting setting;
 
    setting.spec = kCTParagraphStyleSpecifierLineSpacing;
    setting.valueSize = sizeof(CGFloat);
    setting.value = &lineSpacing;
 
    CTParagraphStyleRef paragraphStyle = CTParagraphStyleCreate(&setting, 1);
 
    // Add the paragraph style to the dictionary.
    NSDictionary *attributes = [NSDictionary dictionaryWithObjectsAndKeys:
                               (__bridge id)font, (id)kCTFontNameAttribute,
                               (__bridge id)paragraphStyle,
                               (id)kCTParagraphStyleAttributeName, nil];
    CFRelease(font);
    CFRelease(paragraphStyle);
 
    // Apply the paragraph style to the string to created the attributed string.
    NSAttributedString* attrString = [[NSAttributedString alloc]
                               initWithString:(NSString*)plainText
                               attributes:attributes];
 
    return attrString;
}

在Listing 2-7中，styled字符串用于创建一个framesetter，代码用framesetter创建一个frame并绘制frame。

// Listing 2-7  Drawing the styled paragraph

- (void)drawRect:(CGRect)rect {
    // Initialize a graphics context in iOS.
    CGContextRef context = UIGraphicsGetCurrentContext();
 
    // Flip the context coordinates in iOS only.
    CGContextTranslateCTM(context, 0, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
 
    // Set the text matrix.
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
 
    CFStringRef fontName = CFSTR("Didot Italic");
    CGFloat pointSize = 24.0;
 
    CFStringRef string = CFSTR("Hello, World! I know nothing in the world that has
                                   as much power as a word. Sometimes I write one,
                                   and I look at it, until it begins to shine.");
 
    // Apply the paragraph style.
    NSAttributedString* attrString = applyParaStyle(fontName, pointSize, string, 50.0);
 
    // Put the attributed string with applied paragraph style into a framesetter.
    CTFramesetterRef framesetter =
             CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);
 
    // Create a path to fill the View.
    CGPathRef path = CGPathCreateWithRect(rect, NULL);
 
    // Create a frame in which to draw.
    CTFrameRef frame = CTFramesetterCreateFrame(
                                    framesetter, CFRangeMake(0, 0), path, NULL);
 
    // Draw the frame.
    CTFrameDraw(frame, context);
    CFRelease(frame);
    CGPathRelease(path);
    CFRelease(framesetter);
}

在OS X中，NSView drawRect:方法接收NSRect参数，但CGPathCreateWithRect函数需要一个CGRect参数。 因此，必须使用以下函数调用将NSRect对象转换为CGRect对象：

CGRect myRect = NSRectToCGRect（[self bounds]）;

此外，在OS X中，您可以不同地获取图形上下文，并且不会翻转其坐标，如Listing 2-7中的注释所示。

---

Displaying Text in a Nonrectangular Region - 在非矩形区域中显示文本

在非矩形区域中显示文本的困难部分是描述非矩形路径。 Listing 2-8 中的AddSquashedDonutPath函数返回一个环形路径。 一旦你有路径，只需调用通常的Core Text函数来应用属性和绘制。

// Listing 2-8  Displaying text in a nonrectangular path
 
// Create a path in the shape of a donut.
static void AddSquashedDonutPath(CGMutablePathRef path,
              const CGAffineTransform *m, CGRect rect)
{
    CGFloat width = CGRectGetWidth(rect);
    CGFloat height = CGRectGetHeight(rect);
 
    CGFloat radiusH = width / 3.0;
    CGFloat radiusV = height / 3.0;
 
    CGPathMoveToPoint( path, m, rect.origin.x, rect.origin.y + height - radiusV);
    CGPathAddQuadCurveToPoint( path, m, rect.origin.x, rect.origin.y + height,
                               rect.origin.x + radiusH, rect.origin.y + height);
    CGPathAddLineToPoint( path, m, rect.origin.x + width - radiusH,
                               rect.origin.y + height);
    CGPathAddQuadCurveToPoint( path, m, rect.origin.x + width,
                               rect.origin.y + height,
                               rect.origin.x + width,
                               rect.origin.y + height - radiusV);
    CGPathAddLineToPoint( path, m, rect.origin.x + width,
                               rect.origin.y + radiusV);
    CGPathAddQuadCurveToPoint( path, m, rect.origin.x + width, rect.origin.y,
                               rect.origin.x + width - radiusH, rect.origin.y);
    CGPathAddLineToPoint( path, m, rect.origin.x + radiusH, rect.origin.y);
    CGPathAddQuadCurveToPoint( path, m, rect.origin.x, rect.origin.y,
                               rect.origin.x, rect.origin.y + radiusV);
    CGPathCloseSubpath( path);
 
    CGPathAddEllipseInRect( path, m,
                            CGRectMake( rect.origin.x + width / 2.0 - width / 5.0,
                            rect.origin.y + height / 2.0 - height / 5.0,
                            width / 5.0 * 2.0, height / 5.0 * 2.0));
}
 
// Generate the path outside of the drawRect call so the path is calculated only once.
- (NSArray *)paths
{
    CGMutablePathRef path = CGPathCreateMutable();
    CGRect bounds = self.bounds;
    bounds = CGRectInset(bounds, 10.0, 10.0);
    AddSquashedDonutPath(path, NULL, bounds);
 
    NSMutableArray *result =
              [NSMutableArray arrayWithObject:CFBridgingRelease(path)];
    return result;
}
 
- (void)drawRect:(CGRect)rect
{
    [super drawRect:rect];
 
    // Initialize a graphics context in iOS.
    CGContextRef context = UIGraphicsGetCurrentContext();
 
    // Flip the context coordinates in iOS only.
    CGContextTranslateCTM(context, 0, self.bounds.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);
 
    // Set the text matrix.
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);
 
    // Initialize an attributed string.
    CFStringRef textString = CFSTR("Hello, World! I know nothing in the world that
    has as much power as a word. Sometimes I write one, and I look at it,
    until it begins to shine.");
 
    // Create a mutable attributed string.
     CFMutableAttributedStringRef attrString =
                CFAttributedStringCreateMutable(kCFAllocatorDefault, 0);
 
    // Copy the textString into the newly created attrString.
    CFAttributedStringReplaceString (attrString, CFRangeMake(0, 0), textString);
 
    // Create a color that will be added as an attribute to the attrString.
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGFloat components[] = { 1.0, 0.0, 0.0, 0.8 };
    CGColorRef red = CGColorCreate(rgbColorSpace, components);
    CGColorSpaceRelease(rgbColorSpace);
 
    // Set the color of the first 13 chars to red.
    CFAttributedStringSetAttribute(attrString, CFRangeMake(0, 13),
                                     kCTForegroundColorAttributeName, red);
 
    // Create the framesetter with the attributed string.
    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString(attrString);
 
    // Create the array of paths in which to draw the text.
    NSArray *paths = [self paths];
 
    CFIndex startIndex = 0;
 
    // In OS X, use NSColor instead of UIColor.
    #define GREEN_COLOR [UIColor greenColor]
    #define YELLOW_COLOR [UIColor yellowColor]
    #define BLACK_COLOR [UIColor blackColor]
 
    // For each path in the array of paths...
    for (id object in paths) {
        CGPathRef path = (__bridge CGPathRef)object;
 
        // Set the background of the path to yellow.
        CGContextSetFillColorWithColor(context, [YELLOW_COLOR CGColor]);
 
        CGContextAddPath(context, path);
        CGContextFillPath(context);
 
        CGContextDrawPath(context, kCGPathStroke);
 
        // Create a frame for this path and draw the text.
        CTFrameRef frame = CTFramesetterCreateFrame(framesetter,
                                         CFRangeMake(startIndex, 0), path, NULL);
        CTFrameDraw(frame, context);
 
        // Start the next frame at the first character not visible in this frame.
        CFRange frameRange = CTFrameGetVisibleStringRange(frame);
        startIndex += frameRange.length;
        CFRelease(frame);
}
 
CFRelease(attrString);
CFRelease(framesetter);
}

后记

未完，待续~~~