Core Text a bit smaller than NSString drawInRect:? - objective-c

Question

In theory, these should be the same size, but they're not:
The text in blue is from Core Text, in black is from -[NSString drawInRect:]. Here is the code:
//Some formatting to get the correct frame
int y = MESSAGE_FRAME.origin.y + 8;
if (month) y = y + 27;
int height = [JHomeViewCellContentView heightOfMessage:self.entry.message];
CGRect rect = CGRectMake(MESSAGE_FRAME.origin.x + 8, y, MESSAGE_FRAME.size.width - 16, height);
//Draw in rect method
UIFont *font = [UIFont fontWithName:#"Crimson" size:15.0f];
[[UIColor colorWithWhite:0.2 alpha:1.0] setFill];
[self.entry.message drawInRect:rect withFont:font lineBreakMode:UILineBreakModeWordWrap alignment:UITextAlignmentLeft];
//Frame change to suit CoreText
CGRect rect2 = CGRectMake(MESSAGE_FRAME.origin.x + 8, self.bounds.size.height - y - height, MESSAGE_FRAME.size.width - 16, height);
//Core text method
CTFontRef fontRef = CTFontCreateWithName((CFStringRef)#"Crimson", 15.0f, NULL);
NSDictionary *attDictionary = [NSDictionary dictionaryWithObjectsAndKeys:
(__bridge_transfer id)fontRef, (NSString *)kCTFontAttributeName,
(id)[[UIColor blueColor] CGColor], (NSString *)kCTForegroundColorAttributeName,
nil];
NSAttributedString *attString = [[NSAttributedString alloc] initWithString:self.entry.message attributes:attDictionary];
//Flip the coordinate system
CGContextSetTextMatrix(context, CGAffineTransformIdentity);
CGContextTranslateCTM(context, 0, self.bounds.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, rect2);
CTFramesetterRef framesetter = CTFramesetterCreateWithAttributedString((__bridge_retained CFAttributedStringRef)attString);
CTFrameRef theFrame = CTFramesetterCreateFrame(framesetter, CFRangeMake(0, [attString length]), path, NULL);
CFRelease(framesetter);
CFRelease(path);
CTFrameDraw(theFrame, context);
CFRelease(theFrame);
The font is the same. I don't understand why one is being rendered differently.

Answer 1

It’s because NSLayoutManager uses some unusual heuristics to cope with certain fonts.
See How does line spacing work in Core Text? (and why is it different from NSLayoutManager?) for more detail.