https://bugs.documentfoundation.org/show_bug.cgi?id=142940

--- Comment #20 from Adam Fontenot <[email protected]> ---
Created attachment 178784
  --> https://bugs.documentfoundation.org/attachment.cgi?id=178784&action=edit
animation showing behavior with and without pair kerning

I was poking around with this bug some more and discovered something quite
strange. I'm hoping someone can help me understand it and suggest whether
filing a separate bug report for it would be worthwhile.

The attachment shows the issue. The images in the GIF are subpixel antialiased
and then re-rendered in grayscale using the RGB value of each subpixel. (The
result is point upscaled 3x for clarity.)

The transition from "no pair kerning" to "pair kerning" makes sense, because it
illustrates this bug. Pair kerning makes things worse when subpixel positioning
isn't supported.

The transition from plain Cairo to Cairo with subpixel positioning disabled
also makes sense, because it illustrates why the lack of subpixel positioning
in LibreOffice (bug 103322) is such a big problem.

But the transition from Cairo with no subpixel positioning to LibreOffice is
very strange! They're *similar*, but the position of the two "a" characters is
pretty bad in LibreOffice. This seems to suggest that LibreOffice has another
glyph positioning bug - not only does it not support subpixel positioning, it
frequently doesn't even pick the best *pixel* position, despite Cairo doing so.

Is this a different issue than bug 103322? I'd be happy to report it.

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