[cairo] FreeType internals in new versions of cairo

Keith Packard keithp at keithp.com
Sun Feb 4 12:53:29 PST 2007

On Sun, 2007-02-04 at 14:58 -0500, Behdad Esfahbod wrote:

> The cairo patches on that page are different.  They are not about
> internal headers, but using new API in FreeType 2.3.1 for LCD subpixel
> filtering.  As the comment says: "This patch makes the library use the
> new built-in FreeType LCD color filtering features. You need FreeType
> 2.3.1 (or newer)!"

The Freetype filters work better on unhinted glyphs than the cairo
filter, but the cairo filter works better (to my eye) on hinted glyphs.
The cause is intrinsic in the design of the two filters -- the cairo/Xft
filter is entirely intra-pixel, so a solid pixel doesn't leak out into
the neighboring sub-pixels while the FreeType filter (which is more
'correct' from a simplistic DSP perspective) ignores pixel boundaries
and filters subpixels across both adjacent subpixels.

I haven't considered using the freetype filter for Xft, and I'm not sure
we should for cairo either.

keith.packard at intel.com
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