Fully Integrated Mobile Graphics 2D (FIMG2D or shortened to G2D most of the time) is an intellectual property core used in the Samsung Exynos SoCs offering hardware acceleration for bit block transfers. There are two variants of the G2D core in the wild, revision 3.0 on S5Pv210 and Exynos4210, and revision 4.1 on Exynos4x12, Exynos5 and probably later SoC as well.
Two drivers for the G2D core are available in mainline Linux, one being part of the Exynos DRM driver, and the other a platform media driver. The latter exposes its functionality via the V4L2 API, and supports both revision 3.0 and 4.1 cores. The downside is that it lacks a lot of features, especially for revision 4.1 cores. Also virtually no example code is available for it. The G2D subdriver of the Exynos DRM (DRM-G2D) only supports revision 4.1 cores, but should be considered the actively maintained driver.
Some experimental additions to libdrm can be found in this repository.