Re: FreeType INSTCTRL behavior (Po Lu) (Re: Freetype-devel Digest, Vol 217, Issue 8)

[Hin-Tak Leung]

Perhaps let me ask the opposite question: do you really expect setting projection vector and rp1 in prep to have global effects on every glyph, and/or setting those in one glyph to have effect on another glyph?

In fact, those are per contour / contour fragment values.

Today's Topics:

  1. FreeType INSTCTRL behavior (Po Lu)

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Message: 1

Date: Sun, 12 Feb 2023 23:40:09 +0800

From: Po Lu <luangruo@yahoo.com>

To: freetype-devel@nongnu.org

Subject: FreeType INSTCTRL behavior

Message-ID: <87y1p2yjs6.fsf@yahoo.com" rel="nofollow" target="_blank">87y1p2yjs6.fsf@yahoo.com>

Content-Type: text/plain

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.