2D physics test
https://github.com/kyorohiro/hello_skyengine/tree/master/ph_2d_boun_no_friction
// following code is checked in 2016/01/13
//
2D physics test
https://github.com/kyorohiro/hello_skyengine/tree/master/ph_2d_boun_no_friction
// following code is checked in 2016/01/13
//