Motion and Collision - Beginning Android 3D Game Development - page 147

m_Orientation.GetPosition(),
m_Orientation.GetRotationAxis(),
m_Orientation.GetScale());
}
}

Modifying the MyGLRenderer Class
The MyGLRenderer class must also be modified, because the final program will consist of a cube
that is affected by gravity. A linear upward force is applied to the cube, and a rotational force is
applied to the cube when it hits the ground. The net result is that the cube appears to jump when it
hits the ground and starts spinning faster and faster.

The variable m_Force1 is the linear force that is applied to the cube when it hits the ground level.

private Vector3 m_Force1 = new Vector3(0,20,0);

The m_RotationalForce variable is the rotational force that is applied to the cube every time it hits
the ground.

private float m_RotationalForce = 3;

In the CreateCube() function, Cube.CubeData4Sided is used to provide texture mapping on four sides
of the cube instead of two.

MeshEx CubeMesh = new MeshEx(8,0,3,5,Cube.CubeData4Sided, Cube.CubeDrawOrder);

The gravity for m_Cube is set to true, so that the cube will fall until it hits the ground level.

m_Cube.GetObjectPhysics().SetGravity(true);

In the onDrawFrame() function (see Listing 5-14), new code in bold has been added, which
1. Updates the cube physics by calling UpdateObject3d()

2. Tests if the cube has just hit the ground by calling GetHitGroundStatus()

3. Applies, the upward translational force m_Force1 and the rotational force

m_RotationalForce to the cube, if the cube has just hit the ground

4. Resets the just-hit-ground status

This is the key code that creates the bouncing/rotating cube effect. (See Figure 5-16 .)

Listing 5-14. Modifying the onDrawFrame() Function

@Override
public void onDrawFrame(GL10 unused)
{
GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
GLES20.glClear( GLES20.GL_DEPTH_BUFFER_BIT | GLES20.GL_COLOR_BUFFER_BIT);