[Fontconfig] Changing to hintslight globally by default + hintfull for otfs

[Akira TAGOH]

All the improvement are welcome. though the suggestion may needs
understanding how they behaves on font formats as you mentioned. so I
suppose providing case-by-case examples may be hepful for users. it
can be done in the configuration files without modifying the code at
least.

On Thu, Oct 8, 2015 at 5:39 PM, Nikolaus Waxweiler <madigens at gmail.com> wrote:
> (reposting because I wasn't subscribed to the list)
>
> Hello fontconfig people,
> I'm currently trying to save the world, ehm, bring more order into the
> font rendering world.
>
> The first problem is, I personally don't like hintslight/medium/full
> because they are coarse descriptions that mean different things to
> different font formats:
>
> 1. OpenType/CFF (.otf) fonts: medium == full == snapping glyphs to the
> y-axis only. By design, this tries to preserve outline fidelity.
> 2. TrueType (.ttf) fonts: Full currently (FreeType 2.6.1) snaps to
> x-and-y-axis and FT doesn't fully handle ClearType yet (so no
> y-only-snapping like on Windows). Medium is similar to full, but seems
> to be less aggressive on the x-axis. Both sacrifice outline fidelity and
> "harmoniousness" for absolute sharpness with varying success. Even when
> ClearType is fully handled, it depends on the bytecode in the font if
> you get y-only or x-and-y snapping.
> 3. Postscript fonts: not sure, but the native hinter produces
> sub-optimal results anyway.
> 4. Slight invokes the autohinter regardless of font format. Like for
> .otfs, it snaps to the y-axis only.
>
> The problem is nicely visible when you go medium or full and mix font
> formats. A default installation of Fedora will have Cantarell in
> OpenType/CFF format in the UI and DejaVu (.ttf) on the console.
> Cantarell is y-snapped (and slightly emboldened), DejaVu
> x-and-y-snapped. The difference is jarring.
>
> The second problem is that FreeType currently doesn't fully handle
> ClearType. TrueType fonts developed with ClearType in mind will look
> sub-optimal by default. The OpenType/CFF hint support is top notch in
> contrast, thanks to Adobe's contributed CFF engine. The autohinter has
> been doing a mighty fine job across the board and for different
> languages for a while.
>
>
> I propose that fontconfig defaults to the autohinter == hintslight
> globally and sets hintfull only for OpenType/CFF fonts. That way, the
> default for all fonts is to snap them to the y-axis, leading to a much
> more coherent and harmonious look out of the box. Ubuntu has been doing
> global hintslight for years and I personally found rendering to be
> mostly fine there.
>
> Ideally, fontconfig exposes something like "hintnative", "hintauto",
> "hintnone" and the modifiers "y-only", "x-and-y-if-supported", and
> scraps "hintslight/medium/full" and the "hinting" and "autohint" attributes.
>
> Thoughts?
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-- 
Akira TAGOH