[Fontconfig] strange behavior for font with partial bitmap embedding

[Qianqian Fang]

hi

I am working toward a new CJK font including both the outline
data and embedded bitmap glyphs. The embedded bitmaps only
cover the CJK characters (Hanzi), at 9,10,11,12pt; while the outline
part covers most Latin, Hanzi, Korean, Japanese and other symbols
(35206 characters in total). The font does not include hinting
instructions for now and only include the medium face (therefore
the fake-bolding process is called when needed)

I observed a rather strange behavior with this font, which can be
summarized below:

1. at size 10pt, if I turn on AA+hinting+subpixel rendering, the
Hanzi part are shown correctly, with the embedded bitmaps, however,
the Latin characters were displayed without AA.

http://bbs.dartmouth.edu/~fangq/blog/upload/aa_hinting_subpix.png

2. if I turn on AA+subpixel from my desktop, the
Latin characters were rendered ok, with smooth outlines, but
all normal face Hanzi (suppose to be displayed with the embedded bitmaps)
become blanks (not the bold face).

http://bbs.dartmouth.edu/~fangq/blog/upload/aa_subpix.png

this test was done on Xubuntu 7.04, Xfce 4.4.0,
fontconfig 2.4.2-1ubuntu1, freetype2 2.2.1-5ubuntu1.1
the locale was under zh_CN(similar for other zh_* locales).

Need to mention that the font behaves normal in OpenOffice 2.2:
(for autohinting off)
http://wenq.org/gallery/albums/userpics/10002/zenhei_prezixiao3_openoffice_en.png
(for autohinting on)
http://wenq.org/gallery/albums/userpics/10002/zenhei_prezixiao3_openoffice2_en.png


The reason for making this partially embedded fonts is because
I have seen a strong consensus among the Chinese users that
a pleasing rendering requires bitmaps for Hanzi, and AA for
Latin or low-density glyphs.

I know little about fontconfig, just curious if this behavior
is by design or a potential bug of fontconfig. This font
is not officially released yet, please let me know if you
need a copy to test and debug.

any other feedback on this matter is also appreciated.

Qianqian