Hi,
I am drawing a font using Glyphs, but after I exported the font I found it too large. I can resize the font following some useful discussion in this forum. But I found the UPM concept very confusing. It determines the number of units in an em. And one em will be scaled to the specified point size when the font is in actual use. But where do the upper and lower boundaries of the em lie? I cannot find the place in Glyphs to make the setting. The glyphs seem just floating with the relative amount of extra space above and below not being explicitly specified.
Furthermore, I have seen professional font source file with UPM=2048 but Ascender=1996, Descender=-800. I thought when this font is exported and in actual use the ascender will interact with the descender of the preceding line when there is no extra leading added, but it turned out I was wrong. The font works perfectly without any anomaly. It seems it is not the UPM=2048 units being scaled to the point size but a much larger range was scaled. Do I misunderstand the UPM and em concept?
I apologize if this is a dump question. But I am new to type design and this problem have confused me for several days. Thanks in advance for any comment.
No such thing in digital fonts. UPM is just a measurement for telling how many font units make up the font size (1 em), and 1 em is just the measurement unit for the font size. The font size does not start or end anywhere either.
That depends on the application and the settings the user makes. Different apps have different standards where they place their lines and where they clip (i.e., cut off the glyphs). Most will add a default line gap. Some apps take the line gap values from the font file, some ignore that. I collected some links in the Vertical Metrics tutorial if you want to dig deeper.
Thank you very much for your reply and explanation. I feel less confused now. But still not everything is clear for me. Could you send me the links you mentioned? I would like to dig deeper.
Edit: @mekkablue I am sorry I misunderstood your words. I have found the tutorial and the appended links, thank you very much!
That is not correct, the absolute boundaries are at 2 to the power of 14.
(and in some obscure situations a third of that).
Probably not what this question was about, but with black beyond the boundary, fonts stop working correctly.
Yes, you are right. You are referring to the maximum number that can be stored for a coordinate in a CFF font. Isn’t it 2^14−1, i.e., one less than 2 to the power of 14?
Same limit for for TT fonts?
(And you are also right about the question being different, namely: ‘where is the em’, and you cannot say the em goes from here to here.)
Don’t know about minus one. I ran into the limit just once: a previous version of PowerPoint with a previous rasterizer would render all glyph widths as zero, only when one of the characters within the ANSI subset would be wider than a third of 2^14, only when ClearType was activated. Took me about an hour to pinpoint that obscure bug
I can’t reproduce it today, neither with Office 2010 in Win 7, nor with current PowerPoint in Windows 10. It must have been solved. Even with glyphs extending the border, the font seems to be working fine.
As CFF fonts were based largely on the superior TTF format, they must have inherited the limit from ttf.
Darn, I wanted to brag with TheWidest font, where all glyphs are up to 16384 units in black width, but the limit seems gone. Glyphs flips out around 32000 units, that other font editor starts wrapping around at 2^15, but a ttf generated from that still works, except for the extremely wide glyphs.
The limit of today remains an open question, but better safe than sorry and stay below 2^14.
