[ft] On centering glyphs around vertical baseline

[Dohyun Kim]

Hi,

In vertical rendering mode of freetype, glyphs are placed
center-aligned around vertical baseline, which however seems to be a
bug.

I have done some simple tests and compared the result of freetype
(plus harfbuzz) with those wordpad on windows 8.1 and textedit on mac
os x 10.9.  In all three cases, Source Han Sans [1], a free pan-CJK
font recently released by Adobe, was used. The text used for testing
was <U+65E5 U+302A U+0049 U+004D U+65E5>.

Attached image file is the result of comparison.  As shown in the
image, only freetype puts glyphs center-aligned.  So there seems to be
a bug in freetype's vertical rendering mode.

FYI, this issue has been spotted while pondering over how to support
vertical typesetting of combining Hangul Jamo characters, on which a
discussion is going on at issue tracker of Source Han Sans. [2]

[1] http://sourceforge.net/adobe/source-han-sans/wiki/Home/
[2] https://github.com/adobe-fonts/source-han-sans/issues/34

Best Regards,
-- 
Dohyun Kim
Seoul, Republic of Korea

vertical_bearingX.png
Description: PNG image