Feedback request: Add new RenderingHints.KEY_FONT_HINTING

[Philip Race]

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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