Bug 235554

Description of problem:

The NSimSun font (the Chinese font simsun.ttc from Windows XP) has embedded
bitmaps for the Chinese glyphs at pixel sizes 12-16, but apparently there are no
embedded bitmaps for ASCII characters, as these characters remain antialiased in
ftview even when embedded bitmaps are turned on at the correct sizes.

This font always renders correctly in ftview.  However, two rendering problems
appear in GNOME applications when the font is used at the sizes with embedded
bitmaps:

1. If sub-pixel rendering is turned on, the Chinese characters disappear in many
applications.  The sample in the font selection dialog looks okay, and so does
the text rendered in pango-view, but the Chinese characters disappear in all
GNOME applications if NSimSun is set as the dialog font.

2. If ordinary (not sub-pixel) antialiasing is enabled instead,  the Chinese
characters show up correctly as the embedded bitmaps, but the ASCII characters
(which do not have embedded bitmaps) are barely readable, in particular the
digit "4" at pixel size 16 looks much like "1".  This problem is visible in
pango-view.

The ASCII characters do not appear antialiased at these sizes, and they look
much worse than the "correct" non-antialiased rendering, as if they had been
rendered without hinting, or the antialiased rendering had been converted to
black-and-white before being displayed.

Both problems disappear when I manually disable antialiasing at the sizes with
embedded bitmaps by putting the attached file into /etc/fonts/conf.d.  This
workaround works well, but it is cumbersome to find out all the sizes with
embedded bitmaps.

Version-Release number of selected component (if applicable):

I'm not sure of the exact component causing the problem, so I list some likely
candidates below.  The system is Fedora core 6, and a full update has been done
yesterday.

fontconfig-2.4.1-3.fc6
freetype-2.2.1-16 (rebuilt from the source RPM after turning on the bytecode
interpreter in the spec file)
pango-1.14.10-1.fc6
cairo-1.2.6-1.fc6
libXrender-0.9.1-3.1
xorg-x11-server-Xorg-1.1.1-47.7.fc6

How reproducible:
Always

Steps to Reproduce:
1. Build freetype with bytecode interpreter support (not sure if this is necessary)
2. Set up fonts.conf so that the NSimSun font can be found by fontconfig.
3. Open some GNOME applications with LANG=zh_CN.UTF-8, e.g. by choosing
Simplified Chinese as the language when starting the session.
4. In gnome-font-properties, turn on subpixel rendering, set DPI to 96, and
change the dialog font to NSimSun at 11pt.  After clicking OK, the Chinese
characters in most applications (e.g. the clock applet) should disappear,
including the Chinese messages in gnome-font-properties itself if it had been
started with LANG=zh_CN.UTF-8.
5. Now turn off subpixel rendering and use ordinary grayscale antialiasing.  The
Chinese characters should reappear, but the digits in the clock applet look bad,
in particular the diagonal stroke in "4" totally disappears making it appear
like "1".
6. When antialiasing is disabled at these sizes via the attached fontconfig
file, the result looks correct in both cases.

Actual results:
See above.

Expected results:
The Chinese characters should appear and the ASCII characters should be quite
readable at that size.

Additional info: