Time for action – adding ground to the scene

Most of the times you'll want your object to stay on the screen instead of falling into the abyss. So, let's add some ground that will stop the stone from falling further. Refer to the following steps:

1. Open the PhysicsScene.m file and add the _ground instance variable:

   @implementation PhysicsScene
   {
      //..skipped..
   
      CCSprite *_ground;
   }

2. Then, before adding the ground sprite, add one more z-order #define statement, between kBackgroundZ and kObjectsZ as shown in the following code:

   #define kBackgroundZ    10
   #define kGroundZ        15
   #define kObjectsZ       20

3. Now, add the addGround method as follows:

   -(void)addGround
   {
       //1
       _ground = [CCSprite spriteWithImageNamed:@"ground.png"];
       
       //2
       CGRect groundRect;
       groundRect.origin = CGPointZero;
       groundRect.size = _ground.contentSize;
       
       //3
       CCPhysicsBody *groundBody = 
         [CCPhysicsBody bodyWithRect:groundRect cornerRadius:0];
       
       /...