[squeak-dev] Cuis font sizes
Bert Freudenberg
bert at freudenbergs.de
Sat Aug 29 18:59:16 UTC 2009
On 29.08.2009, at 19:13, Juan Vuletich wrote:
> David T. Lewis wrote:
>> On Sat, Aug 29, 2009 at 12:18:18PM -0300, Juan Vuletich wrote:
>>
>>> I never found a clear specification of the meaning of '12 point',
>>> and I'm totally for making the fonts behave properly.
>>>
>>
>> http://en.wikipedia.org/wiki/Point_(typography)
>>
>> 72 points = 1 inch
>>
>> Dave
>>
> I know that, but those 12 points are the ascent? the height (ascent
> +descent)? the line grid (from a baseline to the next)?
It's the size of the em square. The site linked by Andreas explains it
quite well:
http://www.emdpi.com/emsquare.html
> Why for Freetype, 12 points meanse 15+4 pixels?
It does not. It depends on both the font and the dpi settings. E.g.
this is a sample of Helvetica, Times, and Zapfino, as rendered by
Quartz 2D, at size 12:
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As you can see, Times appears significantly smaller than Helvetica,
while Zapfino appears much larger. However, the em square is the same.
It's up to the font designer.
But the dpi setting is up to us. You should use
TextStyle>>pointsToPixels: to get the em square size in pixels from
the font point size. This defaults to 96 dpi but can be changed. Most
of the system uses that, the only offender I'm aware of is
TTCFontSet>>pointSize which hard-codes 96 dpi. And there might be some
that use the size as is rather than properly converting.
- Bert -
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