RFR: 8312555: Hieroglyphs aren't stretched by AffineTransform.scale(2, 1)

[Phil Race]

On Thu, 17 Aug 2023 20:55:29 GMT, Phil Race <prr at openjdk.org> wrote:

>> **Problem**
>> 
>> Glyphs aren't stretched by applying an affine transform `scale(2, 1)` to a font. Instead, the space between glyphs increases.
>> 
>> **Root Cause**
>> 
>> Bitmaps embedded in the font are used to render the glyphs; the bitmaps aren't transformed, so white-space is seen which fills the requested horizontal size.
>> 
>> **Fix**
>> 
>> Disable using embedded bitmaps if horizontal transform is different from the vertical one.
>> 
>> It's similar to [JDK-8204929](https://bugs.openjdk.org/browse/JDK-8204929) and [JDK-8255387](https://bugs.openjdk.org/browse/JDK-8255387).
>> 
>> **Test**
>> 
>> When embedded bitmaps are used, the right half of the image remains filled with the background colour. The test looks for non-white pixels in the right half of the image. If there are only white pixels in the right half of the image, the test fails; if there are other colours, the test passes.
>> 
>> I can reproduce the problem on Windows only. Without the fix, the test reports 6 failures for "MS Gothic", "MS PGothic" and "MS UI Gothic" fonts when text antialiasing is off and when LCD antialiasing is enabled. If greyscale antialiasing is enabled, the glyphs are stretched as expected, this case was handled in JDK-8204929; it can be used as a workaround.
>> 
>> All client tests pass.
>> 
>> The test could be *headless*, but headless systems, especially with Linux, don't have fonts installed. Without fonts, the test is useless, therefore I made it *headful*.
>
> test/jdk/java/awt/font/FontScaling/StretchedFontTest.java line 50:
> 
>> 48: /*
>> 49:  * @test
>> 50:  * @key headful
> 
> I don't see anything in this test that requires headful.

Ah, I see you wrote
"The test could be headless, but headless systems, especially with Linux, don't have fonts installed.
Without fonts, the test is useless, therefore I made it headful."

In fact they should. We already require this. And it really would be just Linux that's an issue and FWIW I doubt you'll
find CJK fonts with embedded bitmaps on Linux anyway. Microsoft are the only OS vendor that make much use of them.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15335#discussion_r1297763085