RFR: 8312555: Ideographic characters aren't stretched by AffineTransform.scale(2, 1) [v3]

[Phil Race]

On Fri, 18 Aug 2023 13:24:00 GMT, Alexey Ivanov <aivanov 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*.~~
>> 
>> The test is *headless*.
>
> Alexey Ivanov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add a translucent color to the test

> > It was pointed out (privately) that we should say ideographs not hieroglyphs. You can look up the difference.
> 
> @prrace Should we say _“glyphs”_ instead? Latin characters are also affected if the font has embedded bitmaps for them, and the MS Gothic font does.

Well .. CJK fonts are much more likely to have embedded bitmaps, so saying glyphs makes it further away from the problem. I think it is fine as is.

If you want to really express the actual problem in the synopsis then it would be something like
"Embedded bitmaps should be ignored for non-simple uniform scales"
but when the bug was filed it wasn't apparent that was the problem, so the symptom was described, not the problem.

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PR Comment: https://git.openjdk.org/jdk/pull/15335#issuecomment-1688621347