Ios CTRunGetImageBounds返回不准确的结果

我正在使用核心文本来绘制一些文本。我想获得各种运行边界，但当我调用

CTRunGetImageBounds

时，返回的rect大小正确，但位置错误。具体来说，线条原点位于整个文本的末尾

- (void)drawRect:(CGRect)rect
{
    CGContextRef context = UIGraphicsGetCurrentContext();
    self.transform = CGAffineTransformMakeScale(1.0, -1.0);
    CGContextSetTextMatrix(context, CGAffineTransformIdentity);

    [[UIColor whiteColor] set];
    CGContextFillRect(context, self.bounds);

    NSMutableAttributedString* attrString = [[NSMutableAttributedString alloc] initWithString:@"Blue should be underlined."];
    NSRange blueRange = NSMakeRange(0, 4);
    [attrString beginEditing];
    //make all text size 20.0
    [attrString addAttribute:(NSString *)kCTFontAttributeName value:(id)CTFontCreateWithName((CFStringRef)@"Helvetica", 20.0, NULL) range:NSMakeRange(0, [attrString length])];
    //make the text appear in blue
    [attrString addAttribute:(NSString *)kCTForegroundColorAttributeName value:(id)[[UIColor blueColor] CGColor] range:blueRange];
    //next make the text appear with an underline
    [attrString addAttribute:(NSString *)kCTUnderlineStyleAttributeName value:[NSNumber numberWithInt:1] range:blueRange];
    [attrString endEditing];

    CGMutablePathRef path = CGPathCreateMutable();
    CGRect bounds = CGRectMake(10.0, 10.0, 200.0, 200.0);
    [[UIColor redColor] set];
    CGContextFillRect(context, bounds);
    CGPathAddRect(path, NULL, bounds);

    CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attrString);
    CTFrameRef frame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, 0), path, NULL);
    CTFrameDraw(frame, context);

    for (id lineObj in (NSArray *)CTFrameGetLines(frame)) {
        CTLineRef line = (CTLineRef)lineObj;
        for (id runObj in (NSArray *)CTLineGetGlyphRuns(line)) {
            CTRunRef run = (CTRunRef)runObj;
            CGRect runBounds = CTRunGetImageBounds(run, context, CFRangeMake(0, 0));
            NSLog(@"bounds: %@", NSStringFromCGRect(runBounds));

            [[UIColor greenColor] set];
            CGContextFillRect(context, runBounds);
        }
    }

    CFRelease(framesetter);
    CFRelease(frame);
    [attrString release];
}

产生：

---

以下是我的想法。这是完全准确的

CTFrameRef frame = [self _frameWithRect:rect];

NSArray *lines = (NSArray *)CTFrameGetLines(frame);

CGPoint origins[[lines count]];//the origins of each line at the baseline
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins);

NSUInteger lineIndex = 0;
for (id lineObj in lines) {
    CTLineRef line = (CTLineRef)lineObj;

    for (id runObj in (NSArray *)CTLineGetGlyphRuns(line)) {
        CTRunRef run = (CTRunRef)runObj;
        CFRange runRange = CTRunGetStringRange(run);

        CGRect runBounds;

        CGFloat ascent;//height above the baseline
        CGFloat descent;//height below the baseline
        runBounds.size.width = CTRunGetTypographicBounds(run, CFRangeMake(0, 0), &ascent, &descent, NULL);
        runBounds.size.height = ascent + descent;

        CGFloat xOffset = CTLineGetOffsetForStringIndex(line, CTRunGetStringRange(run).location, NULL);
        runBounds.origin.x = origins[lineIndex].x + rect.origin.x + xOffset;
        runBounds.origin.y = origins[lineIndex].y + rect.origin.y;
        runBounds.origin.y -= descent;

        //do something with runBounds
    }
    lineIndex++;
}

---

在使用CTRunGetImageBounds（）或CTLineDraw（）之前，需要在绘制或计算每一行之前通过调用CGContextSetTextPosition（）来设置起始文本位置。原因是CTLine本身不知道从何处开始绘制（或计算），它使用最后一个文本位置，因此需要为其指定XY起点。要获取帧线数组的原点，请使用点数组调用ctFrameGetLineOriginates（）。然后，在绘制或计算每条线之前，通过CGContextSetTextPosition（）设置该线的原点

NSArray*行=（NSArray*）CTFrameGetLines（frame）；
CGPoint原点[[行数]]；//基线处每条线的原点
CTFrameGetLineOriginates（框架，CFRangeMake（0,0），原点）；
int i，行数；
lineCount=[行数]；
对于（i=0；i

最好使用如本答案所示的印刷边界，而不是图像边界，因为前者不需要CGContext。另外，getImageBounds函数的速度要慢几个数量级。2小时后，我在谷歌上偶然发现了圣杯。谢谢。上面的代码对我部分有效。返回错误结果的代码是以下运行边界。origin.y=origins[lineIndex].y+rect.origin.y；runBounds.origin.y-=下降；尽管前面的所有代码都返回了正确的宽度、高度、原点.x。。。起源。y有缺陷。有人知道为什么吗？谢谢你的帮助。

NSArray *lines = (NSArray *)CTFrameGetLines(frame);

CGPoint origins[[lines count]];                              // the origins of each line at the baseline
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins); 

int i, lineCount;

lineCount = [lines count];

for (i = 0; i < lineCount; i++) {
 CTLineRef line = (CTLineRef)[lines objectAtIndex:i];
 CGContextSetTextPosition(context, origins[i].x, origins[i].y);
 CTLineDraw(line, context);
 }