Re: FreeType INSTCTRL behavior (Po Lu)

[Po Lu]

Werner LEMBERG <wl@gnu.org> writes:

>> Here is what the TrueType reference manual says: [...]
>
> Found it!  It's not a bug but a feature.  From file
> `src/truetype/ttobjs.c`, lines 1048ff:
>
> ```
>     /* UNDOCUMENTED!  The MS rasterizer doesn't allow the following */
>     /* graphics state variables to be modified by the CVT program.  */
>
>     exec->GS.dualVector.x = 0x4000;
>     exec->GS.dualVector.y = 0;
>     exec->GS.projVector.x = 0x4000;
>     exec->GS.projVector.y = 0x0;
>     exec->GS.freeVector.x = 0x4000;
>     exec->GS.freeVector.y = 0x0;
>
>     exec->GS.rp0 = 0;
>     exec->GS.rp1 = 0;
>     exec->GS.rp2 = 0;
>
>     exec->GS.gep0 = 1;
>     exec->GS.gep1 = 1;
>     exec->GS.gep2 = 1;
> ```
>
> This is commit a2c7eb188892c6 from 2013, confirmed then by Microsoft
> engineer Greg Hitchcock.
>
> I've just filed
>
>   https://github.com/MicrosoftDocs/typography-issues/issues/1012
>
> so that it gets documented in the OpenType specification.
>
>
>     Werner

Oh, I must've missed that.  Thanks!

BTW, isn't this an incompatible change to TrueType unilaterally made by
MS?  What does Apple's scaler do?