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:
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 -