CoreText简介

CoreText是用于处理文字和字体的底层技术,它直接和Core Graphic（又称为Quartz）打交道。Quartz是一个2d图形渲染引擎，能够处理OS X和iOS的图形显示问题。

Quartz能够直接处理字体和字形，将文字渲染到界面上，也是基础库中为一个可以处理字形的模块。因此，CoreText为了排版，会将需要显示的文本内容，位置和字体字形直接传给Quartz。与其他UI组件相比，它直接与Quartz交互，所以它具有高效的排版功能。

• 底层架构图

UIWebView本身可以作为复杂排版的备选方案

基于CoreText和基于UIWebView相比，具有以下不同之处：

开始代码之前需要清楚几个点

渲染层级如下：

截屏2021-12-28 上午11.09.15.png

我们无法直接控制CTRun的创建过程，但是可以设置控制文本的高度、宽度、对齐方式

对于图片排版，本身是不支持的，但我们可以用特殊空白字符代替
同时设置该字体的为要显示的图片的宽度和高度，这样最后生成的CTFrame实例就会在绘制时，将图片位置预留出来

示例代码

CoreText

整个示例可以分为4个类：

• 用于绘制和显示
• 用于保存会只需要的数据
• 用于解析本地json数据，或者网络下载的json数据
• 用于配置绘制的参数，例如文字大小，颜色，行间距

一、CADisplayView

• 获取画布、设置矩阵、坐标系翻转、镜像翻转是标配
• 绘制之前，CoreTextData 要赋值
• 图片需要单独计算坐标并绘制

#import <UIKit/UIKit.h>
#import "CoreTextData.h"                                                                      

@interface CADisplayView : UIView

@property (nonatomic, strong) CoreTextData *data;

@end

@implementation CADisplayView

- (void)drawRect:(CGRect)rect
{
    [super drawRect:rect];
    // 获取画布上下文
    CGContextRef ref = UIGraphicsGetCurrentContext();
    
    // 坐标系上下翻转
    //对于底层的绘制引擎来说，左下角是（0，0）点，对于UIKit左上角是（0，0）点
    //为了原点一致需要翻转坐标系
    CGContextSetTextMatrix(ref, CGAffineTransformIdentity);
    //翻转后需要将坐标系平移 
    CGContextTranslateCTM(ref, 0, self.bounds.size.height);
    // 镜像翻转
    CGContextScaleCTM(ref, 1, -1);
    
    // 文本帧绘制
    if (self.data)
    {
        CTFrameDraw(self.data.ctframe, ref);
    }
    // 富文本中图片绘制
    for (ImageElementModel *model in self.data.imageArr)
    {
        UIImage *image=  [UIImage imageNamed:model.name];
        CGContextDrawImage(ref, model.frame, image.CGImage);
    }
}

二、CoreTextData

• 很多cell在渲染之前需要计算出高度，所以这里提供了内容高度计算
• 图片需要单独绘制，图片数组保存在data中

#import <Foundation/Foundation.h>
#import <CoreText/CoreText.h>
#import "ImageElementModel.h"

NS_ASSUME_NONNULL_BEGIN

@interface CoreTextData : NSObject

@property (nonatomic, assign) CTFrameRef ctframe; // 文本帧
@property (nonatomic, assign) NSInteger height; // 内容高度
@property (nonatomic, strong) NSArray *imageArr; //图片数组

@end

#import "CoreTextData.h"

@implementation CoreTextData


 - (void)setImageArr:(NSArray *)imageArr
{
    _imageArr = imageArr;
    [self calculateImageRectWithFrame];
}

// 在保存图片时计算图片具体的位置
-(void)calculateImageRectWithFrame
{
    // 从CTFrame中获取所有的Line
    NSArray * arrLines = (NSArray *)CTFrameGetLines(self.ctframe);
    NSInteger count = [arrLines count];
    CGPoint points[count];
    获取每行的原点
    CTFrameGetLineOrigins(self.ctframe, CFRangeMake(0, 0), points);
    
    for (int i = 0; i < count; i ++)
    {
        CTLineRef line = (__bridge CTLineRef)arrLines[I];
        //获取所有的CTRun
        NSArray * arrGlyphRun = (NSArray *)CTLineGetGlyphRuns(line);
        for (int j = 0; j < arrGlyphRun.count; j ++)
        {
            CTRunRef run = (__bridge CTRunRef)arrGlyphRun[j];
            NSDictionary * attributes = (NSDictionary *)CTRunGetAttributes(run);
            
            // 获取delegate
            CTRunDelegateRef delegate = (__bridge CTRunDelegateRef)[attributes valueForKey:(id)kCTRunDelegateAttributeName];
            
            if (delegate == nil)
            {
                continue;
            }
 
            // 获取之前创建delegate传入的dict            
            NSDictionary * dic = CTRunDelegateGetRefCon(delegate);
            if (![dic isKindOfClass:[NSDictionary class]])
            {
                continue;
            }
            CGPoint point = points[I];
            CGFloat ascent;
            CGFloat descent;
            //相对位置
            CGRect boundsRun;
            // 一个图片被特殊字符代替后只是一个CTRun，下面也只会调用一次
            boundsRun.size.width = CTRunGetTypographicBounds(run, CFRangeMake(0, 0), &ascent, &descent, NULL);
            boundsRun.size.height = ascent + descent;
            CGFloat xOffset = CTLineGetOffsetForStringIndex(line, CTRunGetStringRange(run).location, NULL);
            boundsRun.origin.x = point.x + xOffset;
            boundsRun.origin.y = point.y - descent;
            
            CGPathRef path = CTFrameGetPath(self.ctframe);
            //获得View的位置
            CGRect colRect = CGPathGetBoundingBox(path);
            //相对偏移获取image的实际位置
            CGRect imageBounds = CGRectOffset(boundsRun, colRect.origin.x, colRect.origin.y);
            
            NSNumber *index = [dic objectForKey:@"index"];
            
            ImageElementModel *model = [self.imageArr objectAtIndex:[index intValue]];
            
            model.frame = imageBounds;
        }
    }
}

- (void)dealloc
{
    CFRelease(self.ctframe);
}
@end

三、CTFrameParse

• 所有解析结构都是根据业务来的，这里只是参考
• Frame作为返回值，不能立即释放，绘制完成会才可以释放

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>
#import "CoreTextData.h"
#import "CTFrameParseConfig.h"

NS_ASSUME_NONNULL_BEGIN

@interface CTFrameParse : NSObject

+ (CoreTextData *)parseJsonData:(NSString *)path config:(CTFrameParseConfig *)config;


@end

#import "CTFrameParse.h"
#import "TextElementModel.h"
#import <CoreText/CoreText.h>
#import "UIColor+Hex.h"

@implementation CTFrameParse

+ (CoreTextData *)parseJsonData:(NSString *)path config:(nonnull CTFrameParseConfig *)config
{
    CoreTextData *data = [[CoreTextData alloc] init];
    
    NSData *jsonData = [NSData dataWithContentsOfFile:path];
    NSArray *arr = [NSJSONSerialization JSONObjectWithData:jsonData options:NSJSONReadingMutableContainers error:nil];
    
    NSMutableAttributedString *resultString = [[NSMutableAttributedString alloc] init];
    
    NSMutableArray *imageArr = [NSMutableArray array];
    
    for (NSDictionary *dict in arr)
    {
        NSString *type = [dict objectForKey:@"type"];
        if ([type isEqualToString:@"txt"])
        {
            [self parseText:dict result:resultString config:config];
        }
        else if ([type isEqualToString:@"img"])
        {
            [self parseImageData:dict result:resultString imageArr:imageArr config:config];
        }
    }
    
    CTFramesetterRef setter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)resultString);
    
    
    // 计算绘制区域高度
    CGSize restrictSize = CGSizeMake(config.width, CGFLOAT_MAX);
    
    CGSize textSize = CTFramesetterSuggestFrameSizeWithConstraints(setter, CFRangeMake(0, 0), nil, restrictSize, nil);
    CGMutablePathRef pathRef = CGPathCreateMutable();
    UIScreen *screen = [UIScreen mainScreen];
    
    if (textSize.height > screen.bounds.size.height)
    {
        CGPathAddRect(pathRef, NULL, CGRectMake(0, 0, config.width, screen.bounds.size.height));
    }
    else
    {
        CGPathAddRect(pathRef, NULL, CGRectMake(0, 0, config.width, textSize.height));
    }
    
    CTFrameRef frame = CTFramesetterCreateFrame(setter, CFRangeMake(0, resultString.length), pathRef, nil);
    
    data.ctframe = frame;
    data.height = textSize.height;
    data.imageArr = imageArr;
    // 书中的代码有问题，这里不能释放
//    CFRelease(frame);
    CFRelease(pathRef);
    CFRelease(setter);
    return data;
}


+ (void)parseText:(NSDictionary *)dict
           result:(NSMutableAttributedString *)result
           config:(nonnull CTFrameParseConfig *)config
{
    NSString *content = [dict objectForKey:@"content"];
    UIColor *color = [UIColor colorWithHexString:[dict objectForKey:@"color"]];
    UIFont *font = [UIFont systemFontOfSize:[[dict objectForKey:@"size"] floatValue]];
    
    NSMutableParagraphStyle *style = [[NSMutableParagraphStyle alloc] init];
    style.lineSpacing = config.lineSpace;
    style.lineBreakMode = NSLineBreakByWordWrapping;
    style.firstLineHeadIndent = 2;
    
    NSAttributedString *as = [[NSAttributedString alloc] initWithString:content attributes:@{NSFontAttributeName:font,NSForegroundColorAttributeName:color, NSParagraphStyleAttributeName:style}];
    [result appendAttributedString:as];

}

+ (void)parseImageData:(NSDictionary *)dict
                result:(NSMutableAttributedString *)result
              imageArr:(NSMutableArray *)imageArr
                config:(nonnull CTFrameParseConfig *)config
{
    NSString *url = [dict objectForKey:@"url"];
    NSString *name = [dict objectForKey:@"name"];
    NSString *width = [dict objectForKey:@"width"];
    NSString *height = [dict objectForKey:@"height"];
    
    ImageElementModel *model = [[ImageElementModel alloc] init];
    model.url = url;
    model.name = name;
    model.width = [width floatValue];
    model.height = [height floatValue];
    
    [imageArr addObject:model];
    
    NSMutableDictionary *dic = [NSMutableDictionary dictionary];
    [dic setValue:[NSNumber numberWithFloat:model.width] forKey:@"width"];
    [dic setValue:[NSNumber numberWithFloat:model.height] forKey:@"height"];
    [dic setValue:[NSNumber numberWithLong:imageArr.count-1] forKey:@"index"];
    model.dict = dic;
    
    NSAttributedString *as = [self replaceImageDataWithWhiteSpace:model config:config];
    [result appendAttributedString:as];
}

static CGFloat ascentCallback(void *bef)
{
    return [(NSNumber *)[(__bridge NSDictionary *)bef objectForKey:@"height"] floatValue];
}

static CGFloat descentCallback(void *bef)
{
    return 0;
}

static CGFloat widthCallback(void *bef)
{
    return [(NSNumber *)[(__bridge NSDictionary *)bef objectForKey:@"width"] floatValue];
}


+ (NSAttributedString *)replaceImageDataWithWhiteSpace:(ImageElementModel *)model
                                                config:(nonnull CTFrameParseConfig *)config
{

    CTRunDelegateCallbacks callbacks;
    memset(&callbacks, 0, sizeof(CTRunDelegateCallbacks));
    callbacks.version = kCTRunDelegateVersion1;
    callbacks.getAscent = ascentCallback;
    callbacks.getWidth = widthCallback;
    callbacks.getDescent = descentCallback;
    
    CTRunDelegateRef delegate = CTRunDelegateCreate(&callbacks, (__bridge void * _Nullable)(model.dict));
    
    // 使用0xFFFC作为空白站位符
    unichar ojectReplacement = 0xFFFC;
       
   NSString * placeHolderStr = [NSString stringWithCharacters:&ojectReplacement length:1];
   
    NSMutableAttributedString *atStr = [[NSMutableAttributedString alloc] initWithString:placeHolderStr];
    
    CFAttributedStringSetAttribute((CFMutableAttributedStringRef)atStr, CFRangeMake(0, 1), kCTRunDelegateAttributeName, delegate);
    
    CFRelease(delegate);
    return atStr;
}

@end

demo工程