Time for action – running Box2D physics engine

Let's rewrite the DroidBlaster physics engine with Box2D with the following steps:

1. Open the jni/PhysicsManager.hpp header and insert the Box2D include file.

   Define a constant PHYSICS_SCALE to convert the body position from physics to game coordinates. Indeed, Box2D uses its own scale for a better precision.

   Then, replace PhysicsBody with a new structure, PhysicsCollision, that will indicate which bodies entered in collision, as shown in the following:

   #ifndef PACKT_PHYSICSMANAGER_HPP
   #define PACKT_PHYSICSMANAGER_HPP
   
   #include "GraphicsManager.hpp"
   #include "TimeManager.hpp"
   #include "Types.hpp"
   
   #include <Box2D/Box2D.h>
   #include <vector>
   
   #define PHYSICS_SCALE 32.0f
   
   struct PhysicsCollision {
       bool collide;
   
       PhysicsCollision():
           collide(false)
       {}
   };
   ...

2. Then, make PhysicsManager inherit from b2ContactListener. A contact listener gets notified about new collisions each time the...