Javi Ferrer developed a free hardware composer for Exynos 4. It is part of NamelessRom:
Other Gralloc-related commits might be needed as well.
The implementation depends on a change in the smdk4412 kernel:
Furthermore, the NamelessRom smdk4412 kernel was rebased on the Note 2 kernel sources. This rebase was not done for the LineageOS kernel and thus is not included in the Replicant kernel. It needs to be investigated if the required changes can be backported, at least for the Samsung video drivers in
The free hardware composer is also not yet part of LineageOS. Development on their part can be tracked on their Gerrit, e.g.:
Replicant 6.0 currently does not make use of FIMG, Replicant 4.2 has some code in skia:
A newer skia commit to make use of FIMG2D:
Integrating these hardware composer changes could make it possible to use the integrated 2D graphics unit (FIMG2D) for compositing which could improve graphics speed significantly on Replicant. It should work at least on the Galaxy S 3 and Note 2, but it should be possible to make it work for the Galaxy S 2 and Note, too.