postscriptSlantAngle is overriden by italicAngle

In [3]: u = Font()

In [6]: u.info.italicAngle = 10

In [7]: u.info.postscriptSlantAngle = 20

In [8]: t = ufo2ft.compileTTF(u)

In [11]: assert t["post"].italicAngle == 20, t["post"].italicAngle
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-11-e1fd7231bc4c> in <module>
----> 1 assert t["post"].italicAngle == 20, t["post"].italicAngle

AssertionError: 10.0

[moyogo]

Here’s a screenshot of the relevant section of the FLS5 Font Info > Metrics and Dimensions > Key Dimensions panel with the description “Slant is based on FontMatrix and works only in T1”.

Here’s a screenshot of Fontforge with two test fonts produced in FLS5, one with the default Slant angle value and another with a custom Slant angle value set to -12. Note that in FLS5 the source or the generated Win Type 1 fonts are exactly the same except for the Slant angle value whereas in Fontforge the one with the Slant angle set to -12 has slanted glyphs.

Edit: the same is true when exporting OpenType CFF from FLS5 with the slant angle value set, however this does not set the FontMatrix but slants the outlines instead, whereas it sets the FontMatrix in Type 1.

[typesupply]

From the Mac FontLab 5 manual (User manual release 5.1 [5/2006]), page 243:

Slant angle Type 1 fonts can be artificially slanted to get an “oblique” appearance while keeping the actual outlines upright. Enter a slant angle value (in degrees) here and check the result in the Preview panel