Transform.cs

using Microsoft.Xna.Framework;
using System;

namespace Game1
{
    class Transform
    {
        Vector3 position;
        /// <summary>
        /// Location of the transform in world space.
        /// </summary>
        internal Vector3 Position
        {
            get
            {
                return position;
            }
            set
            {
                position = value;
                Console.WriteLine("Updating matrix due to change in positon.");
                UpdateMatrix();
            }
        }

        Quaternion rotation;
        /// <summary>
        /// The rotation in degrees around each axis.
        /// </summary>
        Vector3 blank;
        Quaternion q;
        internal Quaternion Rotation
        {
            get
            {
                matrix.Decompose(out blank, out q, out blank);
                return q;
            }
            set
            {
                rotation = value;
                Console.WriteLine("Updating matrix due to change in rotation.");
                UpdateMatrix();
            }
        }

        Vector3 scale;
        /// <summary>
        /// The amount the transform is scalled in each axis.
        /// </summary>
        internal Vector3 Scale
        {
            get
            {
                return scale;
            }
            set
            {
                scale = value;
                Console.WriteLine("Updating matrix due to change in scale.");
                UpdateMatrix();
            }
        }

        /// <summary>
        /// The transform's world matrix.
        /// </summary>
        internal Matrix Matrix
        {
            get { return matrix; }
            set { matrix = value; }
        }
        Matrix matrix;

        internal Transform()
        {
            Reset();
        }
        /// <summary>
        /// Creates a new transform at the specified
        /// position.
        /// </summary>
        internal Transform(Vector3 position)
        {
            Reset();
            this.position = position;
        }
        /// <summary>
        /// Creates a new transform at the specified
        /// position with the specified rotation.
        /// </summary>
        internal Transform(Vector3 position, Quaternion rotation)
        {
            Reset();
            this.position = position;
            this.rotation = rotation;
            UpdateMatrix();
        }
        /// <summary>
        /// Creates a new transform at the specified
        /// position with the specified rotation and
        /// scale.
        /// </summary>
        internal Transform(Vector3 position, Quaternion rotation, Vector3 scale)
        {
            Reset();
            this.position = position;
            this.rotation = rotation;
            this.scale = scale;
            UpdateMatrix();
        }
        /// <summary>
        /// Restores the transform to a default state.
        /// </summary>
        internal void Reset()
        {
            position = Vector3.Zero;
            rotation = Quaternion.Identity;
            scale = Vector3.One;
            matrix = Matrix.CreateWorld(Vector3.Zero, Vector3.Forward, Vector3.Up);
        }
        Matrix rotationMatrix;
        /// <summary>
        /// Updates the world matrix with stored position rotation and scale values.
        /// </summary>
        private void UpdateMatrix()
        {
            // Wrap angles so they do not exceed multiple rotations.
            rotation = new Quaternion(MathHelper.WrapAngle(rotation.X), MathHelper.WrapAngle(rotation.Y), MathHelper.WrapAngle(rotation.Z), MathHelper.WrapAngle(rotation.W));
            rotationMatrix = Matrix.CreateFromQuaternion(rotation);
            Console.WriteLine("Desired Rotation Forward: " + rotationMatrix.Forward);
            // I'm not sure why we use backwards here, but it gets us desired result.
            matrix = Matrix.CreateLookAt(position, position + rotationMatrix.Forward, rotationMatrix.Up);
            Console.WriteLine("View Forward: " + matrix.Forward);
        }
    }
}