As part of the Android port [of GNU Emacs], I've been writing a module to display TrueType fonts. This includes a TrueType interpreter for instructing fonts.
(Please don't ask why I'm not just using FreeType. Building dependencies for Android is not easy.) AFAIU, as long as a font does not perform an INSTCTRL which sets bit 2 in the instruction control, changes made to the graphics state from the control value program will become the ``default'' state from which glyphs are instructed. However, some CJK fonts perform no INSTCTRL instructions at all, change the projection vector and rp1 from prep, yet FreeType resets both to the X axis and 0 respectively before any glyph programs are run. Am I missing anything? If not, could anyone here tell me where this behavior is documented? Thanks.
