collisionShape: btCollisionShape
btCompoundShape
btCollisionObject
m_collisionShape: btCollisionShapem_worldTransform: btTransform----------------------------------------------------------https://pybullet.org/Bullet/BulletFull/classbtCollisionObject.html
localInertia: btVector3
btConcaveShape
后代有btPlaneShape，btEmptyShape等
btRigidbody
构造：、
btConvexShape
extends
localInertia: btVector3
用质量和碰撞体形状计算localInertia：
motionState: btMotionState
创建：用motionstate更新物体位置：
