move into
https://github.com/kyorohiro/doc_2dgame
https://www.gitbook.com/book/kyorohiro/doc_2dgame/details
https://github.com/kyorohiro/doc_2dgame/tree/master/demo/ironheart
(-)------------(+) x(-) | | | (+) y
clock(-90)|||||---------------(0)|||||(90)
(0) | |(-)-------|----------(+) ( ^ )