[DejaVu-bugs] [Bug 20611] Cursive overlap too small

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=20611





--- Comment #3 from Ben Laenen <bl.bugs at gmail.com>  2009-03-13 05:59:09 PST ---
(In reply to comment #2)
> Yes, turning off autohinting solves the problem, but I don't think this is
> really an option. There would be systems with the autohinting on, and the gap
> would show. (I just turned it back on, to avoid the grayish feeling of text on
> my desktop which makes things unreadable.)

And we just can't solve things for the autohinter. The autohinter could easily
become smarter here (it sees a coordinate beyond the glyph bounds → at least
make sure that that is preserved after the hinting). And if the next version of
freetype changed its autohinting algorithms we could adjust our glyphs again to
match the new results. We've always ignored the autohinter bugs in our fonts,
because we just can't fix things for it, as it's a running target and the
target even moves by changing the options (slight/medium/hard hinting, subpixel
or grayscale hinting).

Furthermore, there's nothing here that says the autohinter won't produce gaps
when the overlap is increased 15 units to both sides.

> Also, I think Microsoft is quite aware that hinting would solve the problem.
> They recommend all fonts to be hinted (or embed bitmaps) anyway. But since
> there is no mention of hinting on the page, I wonder if there are cases that
> even proper hinting can't solve the problem. Microsoft's own Arabic fonts have
> both the hinting and the overlap.

Hinting solves it, it's the nature of how hinting works, as you can align the
outlines to the pixel grid exactly. The overlap is only needed when the glyphs
aren't hinted at all.

> Finally, I think your reasoning calls for no overlaps at all, not 20 units on
> each side.

No, because then you'll get gaps when the hinting is turned off... The 40 units
overlap was chosen because it was at that point when the overlaps didn't
produce the blobs (rendering the same letter twice at the same spot on top of
each other will produce a thick look, as the gray pixels on the outlines are
blackened, it's the same effect here), the curves near the connections could be
preserved and the gaps weren't visible (all when rendered without hinting).

To me, the 70 units overlap on that page is just as arbitrarily chosen.

The overlap in DejaVu was really tested out when I've made the glyphs and this
was how it looked best. If the autohinter makes a mess, that's the autohinter's
problem and not something we can solve.

Actually it would be worse for the autohinter if we increased the overlap, as
the autohinter could then think the oulines have to be rendered a pixel outside
the glyph boundaries. Depending on the exact method (the light hinting options
most likely) this can also result in black blobs on the connections.


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