This pixel manipulation library for the X Server and Cairo how has more ARM performance improvements when it comes to image scaling and separately there are general performance improvements for affine transformations. Besides those two areas with optimizations since Pixman 0.20, the Pixman 0.21.2 development release just carries other bug-fixes and improvements.
These ARM optimizations for Pixman were contributed by Siarhei Siamashka who works as a software engineer for Nokia Finland. The improvements to affine transformations come via another Nordic developer, but this time by Søren Sandmann Pedersen of Red Hat.
The release announcement for Pixman 0.21.2 can be found on the X.Org mailing list.