CTLineGetTypographicBounds的问题

本文介绍了CTLineGetTypographicBounds的问题的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

代码是从中提取的修改。

The code is extracted from SimpleTextInput sampe code, with a bit modification.

创建框架：

self.font = [UIFont systemFontOfSize:18.f];
CTFontRef ctFont = CTFontCreateWithName((CFStringRef) self.font.fontName, self.font.pointSize, NULL);        
self.attributes = [[NSDictionary dictionaryWithObject:(id)ctFont forKey:(NSString *)kCTFontAttributeName] retain];
NSAttributedString *attributedString = [[NSAttributedString alloc] initWithString:self.text attributes:self.attributes];    

_framesetter = CTFramesetterCreateWithAttributedString((CFAttributedStringRef)attributedString);

// Create the Core Text frame using our current view rect bounds
UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.bounds];
_frame =  CTFramesetterCreateFrame(_framesetter, CFRangeMake(0, 0), [path CGPath], NULL);

行下面是框架的任何一行（得到 CTFrameGetLines（_ frame））：

line below is any line of the frame (get by CTFrameGetLines(_frame)):

CGFloat ascent, descent, leading;
CTLineGetTypographicBounds(line, &ascent, &descent, &leading);
CGPoint origin;
CTFrameGetLineOrigins(_frame, CFRangeMake(i, 1), &origin);

问题：

从CTLineGetTypographicBounds或ctFont获得的上升是13.860352，而self.font.ascender是16.860352。这3点差异来自哪里？

下降是4.139648，前导是0，所以上升+下降+前导= 18，但是self.font.lineHeight和行高减去邻近这个4点的差异来自哪里？

CTLineGetTypographicBounds

问题描述

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