I find many good library.
Actually directFB is an good choose but currently it can not compile at all.
First is the one from China, named GuiLite, it has everything I need and its code is really simple, performance is good.
Second is littlevgl, very good interface and light weight.
Third is uGFX, also light weight but not totally free, for test and study it is free.
4th, μGUI, it is too light weight for VoCore2 🙂
I like C better than C++, so I’d like to choose one from littlevgl & uGFX if no better find.