Learning XNA 3.0

Rotating Your Model

Great job! The model is looking good, and you're moving along. It's time to create your first subclass of the BasicModel class, to enable some basic rotation and movement. Right-click the project in Solution Explorer and select Add → Class..., and enter SpinningEnemy.cs as the class name.

Replace the code generated in the SpinningEnemy.cs class with the following code:

using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;


namespace _3D_Game
{
    class SpinningEnemy: BasicModel
    {
        Matrix rotation = Matrix.Identity;

        public SpinningEnemy(Model m)
            : base(m)
        {
        }

        public override void Update(  )
        {
            rotation *= Matrix.CreateRotationY(MathHelper.Pi / 180);
        }

        public override Matrix GetWorld(  )
        {
            return world * rotation;
        }
    }
}

So, what's going on here? The first thing to note is that the SpinningEnemy class derives from BasicModel. The constructor takes a Model and simply passes that model on to the constructor of the base class.

The key addition to this class lies in the class-level variable rotation. This variable allows you to rotate your object rather than just drawing it standing still, the way it was when you drew it using only the BasicModel class. In the Update method, you can see that the rotation variable is updated each frame with a rotation of 1 degree around the Y-axis (remember that angles are represented by radians in XNA; π is 180°, so π/180 equals 1 degree).

Finally, the GetWorld ...