Hello,
the proposed patch is not ideal, as it ignores the Fontconfig LCD filter
settings and produces quite severe color fringes for many fonts.
First, this is not a hinting issue, but an LCD filtering issue. For Qt
to honor the Fontconfig filtering settings in 4.5.0 it needed Freetype
to be built with subpixel rendering support. In that case Freetype does
all the font rendering and filtering and Qt is only used to display the
fonts in the end.
However, if Freetype is not built with subpixel rendering support Qt
does subpixel rendering by using Freetype's gray antialiasing into a
mask that's three times wider than the width of the glyph, and applying
a smoothing filter on the resulting mask. The proposed patch simply
disables the smoothing filter which causes severe color fringes on
certain fonts (especially visible with FreeSans or FreeSerif).
The correct solution when Freetype is built without subpixel
antialiasing support is to fall back to the Qt 3 intrapixel LCD filter
instead of the Qt 4 smoothing filter when the legacy LCD filter setting
is specified in Fontconfig. This will be fixed in Qt 4.5.1 (ref
http://www.qtsoftware.com/developer/task-tracker/index_html?method=entry&id=248387).
The following comparison page shows the differences between no LCD
filtering (as per the proposed patch), default LCD filtering (close to
Qt 4's smoothing filter), and legacy LCD filtering (close to Qt 3's
intrapixel filter): http://www.spasche.net/files/lcdfiltering/
In conclusion I hope you do not include the proposed patch in Debian or
in qt-copy :)
Cheers,
Samuel Rødal
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