On Sep 3, 2008, at 6:01 AM, an0 wrote:
I should declare up front that I know there are some arcane ways to
measure string metrics using things like NSTextStorage,
NSLayoutManager and the kin.
Given the string and the font used to render it, it is reasonable
there should be some straightforward way to tell the metrics of the
string when laid out in one line. Actually, I thought I'd found
several after reading through the docs; however, all of them turned
out to be very miserable.
Here goes what I've tried, with the effects in comments:
NSFont *font = [NSFont labelFontOfSize:12]; // I put the string
in a label
NSRect fontRect = [font boundingRectForFont]; // too large
This is measuring how much space it would take to render any single
glyph. This isn't what you want for measuring text.
NSRect glyphRect = [font boundingRectForGlyph:'W']; // too too
small
Glyphs are not the same thing as characters, and you cannot pass one
in place of the other. The ASCII value of a character is not related
to its glyph value. For example, the glyph corresponding to "W" would
be 58 in the font you were using.
(In fact, you should not think about "glyph value of a character" at
all. Some characters have no glyphs, like space; sometimes multiple
characters produce a single glyph, like an fi ligature.)
In order to generate glyphs from characters, you should use the
methods in NSLayoutManager. However, as you know, this is overkill
for simple text measurements.
IMO, the size of a string with font attribute is an intrinsic property
determined only by the string and the font(and the layout of the
string on the view, but here let's fix the layout to one single line);
and the view used to render the attributed string should have a
reasonalby bigger size to hold the whole string. In other words, one
could have a good guess of the view size from the attributed string
size.
So, if my understanding of these two metrics is right, how can they
differ so much? Was I using the wrong APIs?
If my understanding is wrong, can you tell me what's the exact
relationship between these two metrics?
You were using the wrong APIs. To find the size of a string, use -
[string sizeWithAttributes:]. To find the "natural" size of a control
whose content is some string, use -[[textField cell] cellSize]. As
you surmised, the control's natural size is often "reasonably bigger"
than the content - but it may not be, if the control is fixed size
(such as a circular button).
If you just want a control to be big enough for its content, set the
content on the control and then call -[control sizeToFit].
Hope this helps,
-Peter
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