[ft-devel] Regarding head-table Bit 3: Force ppem to integer values for all internal scaler math

[Behdad Esfahbod]

Hi,

While updating our internal version of FreeType, we noticed some line height
and rasterization changes, which we tracked down to this commit:

b0962ac34e66052ccfee7996e5468f30d4bd5a72 is the first bad commit
commit b0962ac34e66052ccfee7996e5468f30d4bd5a72
Author: Steven Chu <address@hidden>
Date:   Sat Jul 16 09:12:42 2011 +0200

    [truetype] Fix metrics on size request for scalable fonts.

    * src/truetype/ttdriver.c (tt_size_request): Fix copying metrics
    from TT_Size to FT_Size if scalable font.

Indeed, we weren't the first people to notice this.  There's discussion about
it from back in 2012:

  https://lists.gnu.org/archive/html/freetype-devel/2012-04/msg00009.html

Essentially it's about whether FreeType should respect bit 3 of head-table 
flags:

  http://www.microsoft.com/typography/otspec/head.htm

and implemented here:

  https://github.com/behdad/freetype/blob/master/src/truetype/ttobjs.c#L1189

I don't think applying this rounding makes sense when not doing bytecode
hinting.  Indeed, it breaks linear scaling, etc.

What do people think about changing this again?

-- 
behdad
http://behdad.org/