Feedback request: Add new RenderingHints.KEY_FONT_HINTING

Wed Jul 17 18:05:28 UTC 2024

Hi Phil,

Thanks again for the quick response, there's a lot to chew on.

> It crossed my mind that I wasn't sure if we do the right thing
> in this case - the decision to use AA may be seen by the impl
> in a way that it can't tell the origin. This would not be a
> reason to add a new font hinting RenderingHint, it would just
> be a bug. The hinting should only be off if FM=ON and AA=ON
> (not GASP).

Understood, I will set aside some time to put together a minimal test case,
file a bug, and provide the bug ID.

> If you are creating documents to be printed (which is really just
> another hidpi destination like a retina screen) hinting is OFF
> whether you ask for it to be ON or not, because there simply
> won't be hints in the font for that scale. The GASP table for
> example will typically indicate hinting off above something
> like 24 pixel size.

I'm not sure that this is true.

The ttfautohint tool, which is widely adopted and used by many popular open
source fonts, creates a single AA+H (antialiasing + hinting enabled) entry
in the "gasp" table for all sizes. By default it also generates hints for
all sizes between 8 PPEM and 50 PPEM, and only turns off hinting completely
above 200 PPEM. See --hinting-range-min, --hinting-range-max,
--hinting-limit, and "Hint Sets" at [1]. This means using hints for all
sizes under 200 PPEM (by default).

Based on a "gasp" table check in my Windows and Linux system font
directories [2], another popular approach is to suggest AA without hinting
below 8 PPEM or so, and then either (a) enable both AA and hinting for all
sizes above ~8 PPEM, or (b) enable only hinting for sizes between ~8 PPEM
and ~15 PPEM and then enable both AA and hinting above ~15 PPEM. Overall,
most fonts seem to want to enable hinting above 8 or 10 PPEM.

So I do think hints are often available at the sizes that we are discussing.

> the more ways you have to ask for the same thing, then the more
> you have to figure out a sensible answer if two are specified ..
> I am not sure it would ever make sense to specify GASP with ANY
> value of the proposed new hint but you wouldn't be able to stop
> people doing it.
>
> [...]
>
> So my view is this new hint is not needed and potentially
> introduces difficult to answer questions.

Completely agree that a new font hinting "knob" would introduce
combinations of configuration that probably never make sense. And of course
if it doesn't provide value for users, then it's a net negative (just extra
complexity). But I do think this "knob" would be valuable to users, based
on the observation that font hints are common and are sometimes useful,
depending on the application. Indeed, they are separate flags in the "gasp"
table itself (you can enable one, or the other, or neither, or both), so it
seems pretty standard to have two separate "knobs" for these two separate
settings.

As a thought exercise, I went through and thought about which combinations
of AA and hinting might not make sense, and I think the only hard ones
really are just the combinations involving AA GASP. Do you agree? If this
is the case, the options would be to let it happen, or to forbid these two
or three combinations completely. I would be inclined to allow people to
try any of the three AA GASP combinations that they want, with perhaps a
warning in the JavaDoc :-)

AA      HINT        VALID?
--      ----        ------
ON      ON          Y
ON      OFF         Y
ON      DEFAULT     Y
OFF     ON          Y
OFF     OFF         Y
OFF     DEFAULT     Y
DEFAULT ON          Y
DEFAULT OFF         Y
DEFAULT DEFAULT     Y
GASP    ON          ?
GASP    OFF         ?
GASP    DEFAULT     Y

Thanks again for engaging on this topic. I'm off to see about filing that
"FM + AA ON vs FM + AA GASP" bug!

Take care,

Daniel

[1] http://freetype.org/ttfautohint/doc/ttfautohint.html
[2] https://gist.github.com/gredler/a890145b50d4bfc0de1c1e482a52cd5d

On Tue, Jul 16, 2024 at 7:07 PM Philip Race <philip.race at oracle.com> wrote:

>
>
> On 7/15/24 5:11 PM, Daniel Gredler wrote:
>
> Hi Phil,
>
> Thank you for the response and the insights!
>
> I have to admit I don't know much about the situation in macOS, but I
> assume they're moving things in a direction that works best for their
> particular situation (complete control over both the software and hardware
> stacks, and best-in-class displays).
>
> I have indeed experimented with VALUE_TEXT_ANTIALIAS_GASP, and I have two
> problems with this "font knows best" approach:
>
> 1. You're not actually trusting the font to know best. For example, the
> Google Noto Sans Condensed Bold "gasp" table contains a single entry
> indicating that grid-fitting (i.e. hinting) and grayscale rendering (i.e.
> anti-aliasing) should both always be used, at all sizes. However, when I
> use this font in Java with VALUE_TEXT_ANTIALIAS_GASP and
> VALUE_FRACTIONALMETRICS_ON, Java correctly trusts the font regarding AA and
> enables it, but then ignores the font regarding hinting (because currently
> AA + FM = no hinting, and everything else is hinted, regardless of what
> "gasp" says).
>
>
> It crossed my mind that I wasn't sure if we do the right thing in this
> case - the decision to use AA may be seen by the impl in a way
> that it can't tell the origin. This would not be a reason to add a new
> font hinting RenderingHint, it would just be a bug.
> The hinting should only be off if FM=ON and AA=ON (not GASP).
> And it also shows that the more ways you have to ask for the same thing,
> then the more you have to figure out a sensible answer if two
> are specified .. I am not sure it would ever make sense to specify GASP
> with ANY value of the proposed new hint but you wouldn't be
> able to stop people doing it.
>
>
> 2. The font doesn't actually always know best. The application developer
> knows whether they are creating documents to be printed (and if so, whether
> they are intended to be printed on low-DPI or high-DPI devices), whether
> they are creating a desktop application with text animation and scaling
> (like a dynamic reporting dashboard or a videogame), whether they are
> creating a desktop application with static text (like a PDF viewer), etc.
> The developer may want to use one font for all of these use cases, but with
> different rendering hints.
>
>
> if you are creating documents to be printed (which is really just another
> hidpi destination like a retina screen)
> hinting is OFF whether you ask for it to be ON or not, because there
> simply won't be hints in the font for that scale.
> The GASP table for example will typically indicate hinting off above
> something like 24 pixel size.
> But if you are drawing them to the screen to proof for the printer you
> still don't want the rendering to be awful, and that's what you will
> get. Really you just want it laid out properly.
> This is the use case for FM because otherwise text is laid out snapped to
> screen pixels which means it won't scale on a printer.
>
> So my view is this new hint is not needed and potentially introduces
> difficult to answer questions.
>
> -phil.
>
>
> Interestingly, in addition to the three key values that I had proposed
> (VALUE_FONT_HINTING_DEFAULT, VALUE_FONT_HINTING_ON,
> VALUE_FONT_HINTING_OFF), I had actually considered a fourth:
> VALUE_FONT_HINTING_GASP. I didn't include it originally because I think the
> direct control over font hinting is most valuable, but it does make for a
> nice parallel with VALUE_TEXT_ANTIALIAS_GASP, and the combination would
> enable a real "font knows best" mode.
>
> Let me know what you think about these two points and the idea of a fourth
> hinting option.
>
> Take care,
>
> Daniel
>
>
>
> On Mon, Jul 15, 2024 at 9:22 PM Philip Race <philip.race at oracle.com>
> wrote:
>
>>
>>
>> Platforms are tending towards AA+unhinted - this is all we can get from
>> macOS today so I'm not sure how well we could support this hint.
>>
>> And being able to turn off hinting when doing modes such as B&W is
>> unlikely to produce good results on any font you'd want to use.
>>
>> Have you looked at the existing VALUE_TEXT_ANTIALIAS_GASP hint ?
>>
>>
>> https://docs.oracle.com/en/java/javase/21/docs/api/java.desktop/java/awt/RenderingHints.html#VALUE_TEXT_ANTIALIAS_GASP
>>
>> it uses the OpenType table
>> https://learn.microsoft.com/en-us/typography/opentype/spec/gasp
>> which basically tells the rasteriser at a specific size which
>> combination of hinting and anti-aliasing to use.
>>
>> If apps use together with the FM hint they should get most of what they
>> want.
>> Where JDK can (this means when we use freetype) you'd get FM PLUS the
>> appropriate AA PLUS the appropriate hinting choice
>>
>> I think this is better than a hint where an app will have to guess,
>> probably wrongly.
>>
>> -phil.
>>
>>
>> On 7/14/24 7:15 AM, Daniel Gredler wrote:
>> > Hi all,
>> >
>> > We've had a bit of back-and-forth regarding whether font hinting is
>> > enabled or disabled when drawing grayscale text with anti-aliasing and
>> > fractional metrics enabled [1, 2]. Setting AA + FM disabled font
>> > hinting in JDK 8 - 10, then JDK 11 changed this so that AA + FM would
>> > *not* disable hinting, and finally the behavior was reverted in JDK 14
>> > (and backported to JDK 11).
>> >
>> > Generalizing a bit, the current behavior (AA + FM disables hinting) is
>> > optimal for "the desktop use case" (JavaFX, animations, smooth
>> > scaling, etc). The JDK 11/12/13 behavior was optimal for "the backend
>> > use case" (individual image creation, no animations).
>> >
>> > I think it would be useful to have a new java.awt.RenderingHints key
>> > named RenderingHints.KEY_FONT_HINTING, with the following possible
>> values:
>> > - RenderingHints.VALUE_FONT_HINTING_DEFAULT: current behavior,
>> > dictated by AA + FM
>> > - RenderingHints.VALUE_FONT_HINTING_ON: enable font hinting,
>> > regardless of AA + FM
>> > - RenderingHints.VALUE_FONT_HINTING_OFF: disable font hinting,
>> > regardless of AA + FM
>> >
>> > This new rendering hint would allow direct control over whether font
>> > hinting is enabled or not, and would specifically enable the use of AA
>> > + FM + font hints in Java.
>> >
>> > I'm happy to create a patch with this feature (I have a signed OCA on
>> > file), but wanted to get feedback on the idea first. Let me know what
>> > you think!
>> >
>> > Take care,
>> >
>> > Daniel
>> >
>> > [1] https://bugs.openjdk.org/browse/JDK-8214481
>> > [2] https://bugs.openjdk.org/browse/JDK-8242285
>> >
>>
>>
>
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