Re: position of baseline relative to em square

At 11:24 AM -0800 12/1/99, Nick Nussbaum wrote:
> As long as you're explaining things so lucidly;

Thanks  ;-)

> In Adobe fonts are accented Upper Case characters
> always within the Em Square vertical constraints?
> Do Pi/Symbol fonts always fall with in the em square vertical limits?

Definitely not, in either case (pun allowed). Accented lowercase characters
(think of l with acute) may go even higher than accented capitals. And the
glyphs which extend farthest to the left, right and bottom in the Adobe
library are all nonalphabetic symbols of various sorts (oh no - another
typographic pun).

There is no requirement that the font bounding box (the rectangle which
would precisely enclose all the glyphs in the font if they were
superimposed in their proper positions) have any relationship to the em
square. The Type 1 specification states that no glyph should extend more
than 2000 units in any direction from the origin (the 0,0 coordinate in the
context of a 1000-unit em square), theoretically limiting bounding boxes to
four times the height and width of the em - but although it's not
recommended, I know of glyphs that go farther in width or depth (not height
yet).

Environments which need to be concerned with glyph extent (e.g. for
clipping purposes) should check font bounding boxes, followed by glyph
bounding boxes if necessary. But for optical and typographic purposes,
nominal ascent and descent are useful for glyph placement, and should not
be tied to bounding box height, depth or width.

- David Lemon

Received on Thursday, 2 December 1999 11:40:25 UTC