Bug 29411

Summary:	GTK software doesn't use correct lcdfilter unless manually set
Product:	Mageia	Reporter:	Dan Robinson <dlrobin874>
Component:	RPM Packages	Assignee:	Thierry Vignaud <thierry.vignaud>
Status:	NEW ---	QA Contact:
Severity:	minor
Priority:	Normal
Version:	8
Target Milestone:	---
Hardware:	All
OS:	Linux
Whiteboard:
Source RPM:	fontconfig-2.13.93-4.mga8.src.rpm	CVE:
Status comment:

Description Dan Robinson 2021-08-26 03:53:59 CEST

At least under Plasma desktop. Apps tested are Firefox, net_applet, other MCC stuff, Gnome Disks, Gimp. All show severe color fringing with RGB subpixel antialising enabled.

If I manually set lcddefault as the system filter by running `ln -sf /usr/share/fontconfig/conf.avail/11-lcdfilter-default /etc/fonts/conf.d` that clears everything up.

Otherwise the GTK apps appear to default to not being filtered at all and have severe color fringing on the fonts.

I haven't tested under another DE. At least on Fedora it still is an issue but only Plasma defaults to using subpixel RGB antialiasing so it doesn't show up unless you mess with the settings on Gnome.

It looks like the issue is really in Cairo which should be using a sensible default but that isn't getting fixed upstream at all, see https://gitlab.freedesktop.org/cairo/cairo/-/merge_requests/1

And this seems a lot less invasive than maintaining a downstream patch of Cairo (and I think Firefox needs its own override, see https://bugzilla.redhat.com/show_bug.cgi?id=1645763). If we'd rather change that feel free to reassign but I think fixing it in fontconfig makes the most sense as a downstream distro.

Comment 1 Lewis Smith 2021-08-26 21:20:14 CEST

This is all subtle: RGB subpixel antialising !
Thank you for the report, with its references and your own remedy:
> `ln -sf /usr/share/fontconfig/conf.avail/11-lcdfilter-default
> /etc/fonts/conf.d`
> that clears everything up.
Assigning initially to Thierry who has had most to do with fonconfig recently.

Assignee: bugsquad => thierry.vignaud