Re: [ft-devel] Alignment of top of capital letters to pixel grid, autohinter often 1 pixel off compared to unhinted outline

[Nikolaus Waxweiler]

> [At 10 ppem the auto-hinter *enlarges* glyphs, so you probably mean a
> different size]

I meant both enlarging and compressing.

> The auto-hinter tries to align lowercase glyphs with the grid (cf. the
> AF_BLUE_STRING_LATIN_SMALL string in file `afblue.dat', as used in the
> AF_BLUE_STRINGSET_LATN set assigning the
> AF_BLUE_PROPERTY_LATIN_X_HEIGHT property).  This is essential to
> increase legibility at small sizes.  This alignment happens *before*
> hinting; it is done by scaling all glyphs vertically.
>
> Internally, the auto-hinter rounds the x-height more often up than
> down, but if a there is a rounding down, the uppercase glyphs are also
> scaled down, causing the effect you are observing.

Hm, but I thought increasing the x-height is disabled by default because 
..._MAX is set to 0? ftview doesn't change that number. I set ..._MAX to 
15 to test this and it only changed x-height in OpenSans-Regular below 
10ppem. The compression of capital letters didn't change at larger sizes.

Is this effect maybe related to missing subpixel hinting? Stems must be 
snapped to integer positions and at some sizes, this unfortunately snaps 
them 1 pixel too low? I haven't seriously looked at the hinting 
facilities yet.