[Webkit-unassigned] [Bug 260196] Full hinting broken by subpixel positioning

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=260196

--- Comment #3 from Michael Catanzaro <mcatanzaro at redhat.com> ---
(In reply to Pierre Ossman from comment #2)
> Could it be that subpixel positioning is the new default in cairo, and
> WebKit needs to do something explicit to turn it off?

Maybe and maybe.

> That merge request for GTK shows some extra cairo calls. Could those be
> relevant for WebKit?

Maybe.

Truth is, nobody here understands font rendering except Carlos Garcia, and he is telling me "I don't know." I will try asking around, but we probably won't change anything unless a font expert decides to get involved and tell us specifically what to do.

What I do know is that subpixel positioning is incompatible with hinting, so you need to do only one or the other in a particular direction (horizontal or vertical). By default, FreeType does vertical hinting only and does not perform horizontal hinting, so horizontal subpixel positioning should be OK, but we need to make sure not to do any vertical subpixel positioning. It sounds like there are not currently any problems with that.

But when you configure "full" hinting (which is not recommended by the FreeType developers and font experts I have talked to) then hinting may be performed horizontally too, so then we need to make sure we are additionally not doing any horizontal subpixel positioning. Sounds like something is wrong there.

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