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

[Alexey Ivanov]

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 gives correct rendering in this case because LCD antialiasing is replaced with greyscale one. As we already know, greyscale AA disables using embedded bitmaps.
> >
> So by way of explanation, Microsoft always used available embedded bitmaps in LCD mode, but of course once we stretch, we aren't able to use embedded bitmaps and it becomes LCD. Adding translucency then disables LCD so in that case it becomes greyscale.

I think the key here is _“adding translucency ~~then~~ disables LCD so in that case it becomes greyscale.”_ That is translucency converts LCD AA to greyscale AA.

If LCD AA is enabled with opaque black colour, the embedded bitmaps were still used even with a transform applied.

The test in this PR fails if AA is *off* and if AA is *LCD*.

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PR Comment: https://git.openjdk.org/jdk/pull/15335#issuecomment-1684226926