Re: [ft-devel] New `slight' auto-hinting mode

[Alexei Podtelezhnikov]

On Tue, May 16, 2017 at 2:12 AM, Werner LEMBERG <address@hidden> wrote:
>> Currently there is a need to adjust pen position when hinting places
>> two adjacent glyph edges too near or too far.  This concept does not
>> go away with subpixel pen positioning.
>
> Why do you think so?  Where is the difference to the integer case?

Let's trace all the steps backwards. Let's consider usual glyphs with
two well defined edge stems: a, b, d, e, g, h, n, o, p, q, s, u. Let's
pick a size when these edge stems have width not exactly but close to
one pixel. Hinting regardless of shift should produce consistent
images of the same width with the edge stems covering exactly one
pixel. Now think of a word "unabandoned". In order to look good every
hinted stem should have very predictable position. What is also true
is that the pen position is also quite prescribed exactly in the
middle between letters, which because of hinting happens to be either
at the pixel boundary or exactly in the middle of the pixel. As a
consequence, the advance width must also be integer distance either
between pixel boundaries or between the middles.

I honestly do not see how you can achieve predictably periodic regular
hinted look of "unabandoned" with fractional advance. Any accumulating
errors of fractional advance will ruin the hinted look. I think it is
obvious that hinting simply contradicts to fractional advance and
subpixel positioning.