On Fri, Mar 2, 2012 at 5:10 PM, Werner LEMBERG
<address@hidden> wrote:
As the documentation describes, the scaling value of `nominal' is the
units per EM, and the scaling value of `real dim' is the sum of the
ascender and the descender (since descender has negative values if
below the baseline, it's actually a subtraction):
scaling_nominal = face->units_per_EM
scaling_realdim = face->ascender - face->descender
Remember, these values are *scaling values*. Consequently, to
transform from one scaling framework to another, simply compute the
quotient and use it as a factor.
Using arial (version 5.06), I get
face->ascender = 1854
face->descender = -434
units per EM = 2048
This gives
1854 + 434
f = ------------ = 1.11719...
2048
In your example, the `real dim' font size is 40, thus the `nominal'
font size is
40 / 1.11719 = 35.804...
which rounds to 36, as you've deduced by experimentation.
It would be great if you could provide a patch to enhance the
documentation in case you consider it as necessary.
Werner