Time for action – computing normals

To complete the normals, perform the following steps:

1. 1. Near the end of the BuildVertexBuffer() method of the Terrain class, modify the code that defines the vertexBuffer variable by changing BufferUsage.WriteOnly to BufferUsage.None. The new statement should read as follows:

   vertexBuffer = new VertexBuffer(
       device,
       typeof(VertexPositionNormalTexture),
       vertices.Length,
       BufferUsage.None);

2. 2. Similarly, near the end of the BuildIndexBuffer() method, when the indexBuffer is defined, change BufferUsage.WriteOnly to BufferUsage.None. The statement should be as follows:

   indexBuffer = new IndexBuffer(
       device,
       IndexElementSize.SixteenBits,
       indices.Length,
       BufferUsage.None);

3. 3. In the Helper Methods region of the Terrain class, add the CalculateNormals() method as follows:

   private void CalculateNormals()
   {
       VertexPositionNormalTexture[] vertices = 
           new VertexPositionNormalTexture[vertexBuffer.VertexCount];
       short[] indices...