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

A couple of screenshots of `ScaledFont.java` that's attached to the [JBS issue](https://bugs.openjdk.org/browse/JDK-8312555). The screenshots are taken on an English version of Windows 10.

Without the fix:  
![Screenshot of ScaledFont.java running on a recent build of JDK 22 from the CI on an English version of Windows 10. The text rendered with "MS Gothic" font has extra space between the glyphs, they're not stretched.](https://github.com/openjdk/jdk/assets/70774172/460c70c2-b620-416e-abf2-9f6cca1b679f)  
The *MS Gothic* font is affected: both English characters and hieroglyphs have extra space between the glyphs rather than being stretched.

With the fix:  
![Screenshot of ScaledFont.java running on a development build of JDK 22 with the proposed fix on an English version of Windows 10. All the text, including the one rendered with "MS Gothic" font, has stretched glyphs.](https://github.com/openjdk/jdk/assets/70774172/5171f7b1-f382-4a9e-a4d5-06777ad14c8a)  
All the characters are stretched as expected.

I modified the `ScaledFont.java` app to use a translucent color for rendering the text and enabled LCD text antialiasing for the first row (which uses `deriveFont(transform)`). @mrserb is right, 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.  
![Screenshot of ScaledFont.java running on a recent build of JDK 22 from the CI on an English version of Windows 10. The text is rendered with a translucent colour, the first row for each font enables LCD text antialiasing, and the glyphs are stretched in this case.](https://github.com/openjdk/jdk/assets/70774172/c92f54c4-fb7d-4d58-b88d-2aa59790f475)

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PR Comment: https://git.openjdk.org/jdk/pull/15335#issuecomment-1684032432