RFR: 8360136: RFE: Add TextAttributes for OpenType font figure style features

[Phil Race]

On Mon, 14 Jul 2025 13:43:40 GMT, Nikita Gubarkov <ngubarkov at openjdk.org> wrote:

>> @prrace about tests. I can draw test image with font which is support tnum feature, and validate without it. Primitive one.
>> 
>> For example
>>  * at start - need load font, which supports this features. For example `Inter` (also need attach license of it inside repo?)
>>  * draw image `0123456789` with `pnum` 
>>  * <img width="200" height="50" alt="pnum" src="https://github.com/user-attachments/assets/2e80a463-a608-425f-a264-6097e415d397" />
>>  * draw image `0123456789` with `tnum`
>>  * <img width="200" height="50" alt="tnum" src="https://github.com/user-attachments/assets/62600f4e-1094-4fce-bd09-3876b4a8610e" />
>>  * if all bytes of images equals - it's means `tnum` not works. 
>> 
>> Also check default instance of `Font` without options
>> 
>> We can add this images inside repo, and validate image drawing (not sure)
>
> @VISTALL You can take a look at https://github.com/openjdk/jdk/blob/bcd86d575fe0682a234228c18b0c2e817d3816da/test/jdk/java/awt/font/TextLayout/FormatCharAdvanceTest.java - it has a good example of synthetic font generated specifically for the test and embedded into the test as base64. This avoids the hussle with licences and whatnot.
> I would also suggest to avoid golden-image tests, as those tend to be burdensome to maintain. But in your case you can probably inspect line metrics and compare the widths of a sample text.

> @YaaZ Thanks for example. About API. Will be good to make universal api - but I think it's too big task will be.
> 
> Maybe introduce api like nio2 - CopyOption* etc.
> 
> for example
> 
> ```java
> interface FontFeature<V> (FontExtension?) {
>    // some code
> }
> 
> // V is Integer? or delegate to impl
> class OpenTypeFontFeature implements FontFeature<Integer > {
>    OpenTypeFontFeature (String name) {
>    }
> }
> 
> public final class OpenTypeFontFeatures {
>     FontFeature<Integer> TABULAR_NUMBERS = new OpenTypeFontFeature<> ("tnum");
> } 
> ```
> 
> There few questions:
> 
> * conflicting features?
> * need method `Font#supportsFeature(FontFeature)` ?
> * need opentype class? or utilize to default font naming? (eg FontFeatureImpl)
> * need make public `OpenTypeFontFeature` class? (accesing from clients)
> * FontFeature will be extends TextAttribute?

I have previously prototyped APIs in this area. And they inter-operate with other ideas.
I'm working on other things right now so I can't switch gears to that but it probably does make sense to pause on this until I can think about whether this API on its own makes sense.

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PR Comment: https://git.openjdk.org/jdk/pull/26144#issuecomment-3156744114