Re: NSAttributedString boundingRectWithSize vs. paragraph margins
Re: NSAttributedString boundingRectWithSize vs. paragraph margins
- Subject: Re: NSAttributedString boundingRectWithSize vs. paragraph margins
- From: Kyle Sluder <email@hidden>
- Date: Fri, 25 Jan 2013 18:14:11 -0800
I just made a demo project to explore what the heck values
NSStringDrawing is returning:
https://github.com/kylesluder/NSStringDrawer
The line fragment results seem sensible to me, and both the glyph origin
and line fragment results make sense when using device metrics, but
asking for the baseline-rendering-mode glyph origin with a nonzero head
indent returns a rect that always lies at x=0.
This runs contrary to the docs for
-boundingRectWithSize:options:attributes:, which state "the rect origin
returned from this method is the first glyph origin."
If this were the case, constructing a text system and querying the
layout manager for -locationForGlyphIndex:0 clearly shows us that we
should expect a rect that is offset by the amount of the first-line head
indent.
I've filed rdar://problem/13091382 on this issue, but fixing it would
produce a significant-enough change that I think Apple will be very
hesitant to fix it.
--Kyle Sluder
On Thu, Jan 24, 2013, at 12:13 PM, Kyle Sluder wrote:
> On Thu, Jan 24, 2013, at 11:52 AM, Kyle Sluder wrote:
> > > I expect this method to tell me the size of a rectangle (e.g. a bitmap
> > > context) such that if I draw my attributed string into that rectangle, it
> > > will all fit. When I say "all" I mean "all", including the margins.
> >
> > Considering the method is named -boundingRect…, I wouldn't expect this.
> > What you're looking for is the line fragment rect, and I can understand
> > why you would think passing NSStringDrawingUsesLineFragmentOrigin as an
> > option would yield this information. Instead, it seems to offer the
> > bounding rect of the glyph range in line fragment coordinates, which I
> > would surmise is more useful information in NSStringDrawing's primary
> > intended use cases.
>
> Huh, I just tried this in python and I got results that more closely
> match _your_ expectation, not _mine_:
>
> >>> ps = AppKit.NSMutableParagraphStyle.alloc().init()
> >>> ps.setHeadIndent_(20)
> >>> ps.setFirstLineHeadIndent_(30)
> >>> attrs = {AppKit.NSParagraphStyleAttributeName : ps}
> >>> attributedString = Foundation.NSAttributedString.alloc().initWithString_attributes_("A", attrs)
> >>> attributedString.boundingRectWithSize_options_(Foundation.NSMakeSize(1000, 1000), AppKit.NSStringDrawingUsesLineFragmentOrigin)
> <NSRect origin=<NSPoint x=0.0 y=0.0> size=<NSSize width=38.00390625
> height=15.0>>
>
> >>> attributedString.boundingRectWithSize_options_(Foundation.NSMakeSize(1000, 1000), 0)
> <NSRect origin=<NSPoint x=0.0 y=-3.0> size=<NSSize width=8.00390625
> height=15.0>>
>
> Note that when I pass NSStringDrawingUsesLineFragmentOrigin, I get a
> width of 38 points, whereas if I omit it, I get a width of 8.
>
> But if I then add a tailIndent of 40, my metrics don't grow at all:
>
> >>> ps.setTailIndent_(40)
> >>> attributedString.boundingRectWithSize_options_(Foundation.NSMakeSize(1000, 1000), AppKit.NSStringDrawingUsesLineFragmentOrigin)
> <NSRect origin=<NSPoint x=0.0 y=0.0> size=<NSSize width=38.00390625
> height=15.0>>
>
> >>> attributedString.boundingRectWithSize_options_(Foundation.NSMakeSize(1000, 1000), 0)
> <NSRect origin=<NSPoint x=0.0 y=-3.0> size=<NSSize width=8.00390625
> height=15.0>>
>
> So my current theory is that the advancement of the glyph is taken into
> account when computing the glyph's bounding box in line fragment origin
> mode. But that makes me a little surprised that the x-coordinate of the
> origin of the baseline-relative rect is 0 in all cases; I would expect
> it to include the glyph advancement (30).
>
> --Kyle Sluder
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