[ft-devel] Tweak CJK Blue zone parameters

[Just Fill Bugs]

Now that the CJK blue zone code are in the freetype repository, further 
tweak on the parameters can be performed.

One thing that I can think of is that the threshold of best_dist0 used 
in the af_cjk_hints_compute_blue_edges(). best_dist0 is used to 
initialize the snap distant from edges to one of the blue zones.

It's initially set to 1/40 of EM, and scaled to the rendering size. That 
means any edge that is closer to 1/40 of the EM (1024 or something) 
points toward a blue zone will snap to the blue zone.

At smaller rendering size, we can have much less possible different 
edges in limited space. For example, at 16 pixel, we can only have
1/16 different edges, less than the 1/40. (more different edges when 
considering anti-alias rendering, but that's fuzzy.)

Therefore, we can force a bigger snap distance so that we can have more 
uneven edges aligned. Especially when we deliberately merge some glyph 
features at the smaller font size.

What's the suitable snap distance will vary over fonts. I wrote a patch 
to set the distance at 1/24 for 16px or smaller font size. Different 
numbers can be used to experiment with all kind of fonts.

More dynamic adjustment can be archived by linking the best_dist0 value 
to the delta between filled/unfilled blue zones.

cjk-bluezone-tweak.patch
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