CTFrameGetLineOrigins为单行文本获取不正确的起源Y.

Question

CTFrameGetLineOrigins的奇怪行为：

1. 如果我有多行文字 - 它会返回Y的正确值;
2. 如果只有一行文字，则返回错误的值。

这是一个错误还是我错过了什么？

正确的结果：

line:         0
self height:  48.000000
origins y:    35.000000
ascent:       13.328000
descent:      3.374000

结果不正确：

line:         0
self height:  16.000000
origins y:    15.000000
ascent:       13.328000
descent:      3.374000

代码：

CGRect textRect = [self textRectForBounds:self.bounds limitedToNumberOfLines:self.numberOfLines];

CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, textRect);
CTFrameRef frame = CTFramesetterCreateFrame([self framesetter], CFRangeMake(0, (CFIndex)[self.attributedText length]), path, NULL);
if (frame == NULL) {
    CFRelease(path);
    return nil;
}

NSArray* lines = (NSArray*)CTFrameGetLines(frame);
CFIndex lineCount = [lines count];

CGPoint origins[lineCount];
CTFrameGetLineOrigins(frame, CFRangeMake(0, 0), origins);

for(CFIndex idx = 0; idx < lineCount; idx++)
{
    NSLog(@"origin %d: x=%f, y=%f", (int)idx, origins[idx].x, origins[idx].y);

    CTLineRef line = CFArrayGetValueAtIndex((CFArrayRef)lines, idx);

    CFArrayRef glyphRuns = CTLineGetGlyphRuns(line);
    CFIndex glyphCount = CFArrayGetCount(glyphRuns);
    for (int i = 0; i < glyphCount; ++i)    {
        CTRunRef run = CFArrayGetValueAtIndex(glyphRuns, i);
        CGRect runBounds;

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

        runBounds.origin.x = CTLineGetOffsetForStringIndex(line, CTRunGetStringRange(run).location, NULL);
        runBounds.origin.y = self.frame.size.height - origins[idx].y - ascent;
        NSLog(@"\n\
              line:             %d\n\
              self height:      %f\n\
              origins y:        %f\n\
              ascent:           %f\n\
              descent:          %f", (int)idx, self.frame.size.height, origins[idx].y, ascent, descent);
    }
}