On Monday, 13 February 2023 at 15:30:06 GMT+8, Po Lu <[email protected]>
wrote:
Werner LEMBERG <[email protected]> writes:
>>> It's not a bug but a feature. [...]
>>
>> BTW, isn't this an incompatible change to TrueType unilaterally made
>> by MS? What does Apple's scaler do?
>
> I have no idea. Given that (a) Apple doesn't really support hinting
> anymore in macOS, and (b) there wasn't a problem report in the last
> ten years related to this INSTCTRL feature I think it doesn't matter.
>
> Maybe the OpenType standard's editor Peter Constable will contact
> Apple to get a clarification w.r.t. my documentation issue report.
>
>
> Werner
I think it is probably mis-documented - the projection vector and rp1 are not
even per-glyph/contour parameter, but per contour fragment. I can't think of a
good reason of having non-default but uniform values set per font in prep
applying to all glyphs - given that both the projection vector and rp1
typically change a few times even within a single glyph.
Contrary to what Microsoft might like to tell people... the MS font scaler was
licensed from Apple, and despite many years of enhancements, changes, and
additions, in some aspects still behave the same way. (Not sure about this
particular behavior, but it would not surprise me that this MS behavior was
directly *inherited* from Apple's).
