/// <summary>
/// The CollisionMesh class stores a list of CollisionTriangle objects that compose the mesh.
/// The mesh keeps a quick access array of vertex positions in world coordinates that is used
/// to define the CollisionTriangles. This class also stores the CollisionTree that contains
/// this mesh.
/// </summary>
public class CollisionMesh : AccessibleMesh
{
	/*
	 * CLASS PROPERTIES
	 */
	/// <summary>
	/// the collision tree for optimized collision detection
	/// </summary>
	protected CollisionTree collisionTree;
	/// <summary>
	/// the array of vertices in world coordinates
	/// </summary>
	private Vector3[] worldPositions;
	/// <summary>
	/// the array of triangular collidable faces that compose this mesh
	/// </summary>
	private CollisionTriangle[] collisionTris;
	/// <summary>
	/// a bounding box defined in world aligned coordinate space
	/// </summary>
	private BoundingBox worldBounds;

	/*
	 * CONSTRUCTORS
	 */
	/// <summary>
	/// Constructor for a collideable mesh. This constructor
	/// simply relies on its parent class's constructor.
	/// </summary>
	/// <param name="modelName"></param>
	/// <param name="newGame"></param>
	/// <param name="model"></param>
	public CollisionMesh(string meshName, TwelveCylinderGame newGame, ModelMesh mesh)
		: base(meshName, newGame, mesh)
	{
	}


	/// <summary>
	/// gets the world position of the vertex at index i
	/// </summary>
	/// <param name="i">a vertex index</param>
	/// <returns>the world coordinate position of the vertex</returns>
	public override Vector3 getWorldPosition(int i)
	{
		return worldPositions[i];
	}

	/*
	 * COLLISION DATA UPDATES
	 */
	/// <summary>
	/// update the array of collision faces to the current world coordinates
	/// </summary>
	public void updateCollisionFaces()
	{
		foreach(CollisionTriangle triangle in collisionTris)
			triangle.updateAll();
	}

	/// <summary>
	/// updates the array of vertex positions in world coordinates
	/// </summary>
	public void updateWorldPositions()
	{
		if (worldPositions == null || worldPositions.Length != vertices.Length)
			worldPositions = new Vector3[vertices.Length]; //create array of vertices

		//transform each vertex in mesh from local coordinates to worlds coordinates
		for (int i = 0; i < vertices.Length; i++)
			worldPositions[i] = Vector3.Transform(vertices[i].Position, WorldMatrix);

		//update the world bounding box
		worldBounds = BoundingBox.CreateFromPoints(worldPositions);
	}

	/// <summary>
	/// Creates the collision tree used for
	/// collision detection for this mesh.
	/// </summary>
	/// <param name="maxNumDivisions">the maximum number of divisions for the tree</param>
	/// <param name="minTreeNodeVolume">the minimum volume threshold for a tree node</param>
	public void createCollisionTree(uint maxNumDivisions, float minTreeNodeVolume)
	{
		if (collisionTree != null)
			collisionTree.unload(false); //unload existing collision tree

		//create new collision tree definition
		collisionTree = new CollisionTree(curGame, this.Name + " collision tree",
										   new Bounds(curGame, worldBounds.Min, worldBounds.Max),
										   collisionTris, maxNumDivisions, minTreeNodeVolume);
		this.addChild(collisionTree); //add the collision tree to scene hiearchy
	}

	/// <summary>
	/// Creates the array of collideable faces from the
	/// array of vertices and input vertex index array.
	/// </summary>
	/// <param name="indices">the array of vertex indices taht define the mesh triangles</param>
	/// <remarks>called from within the SimpleMesh parseMesh method</remarks>
	protected override void createTriangleDefinitions(int[] indices)
	{
		//collision triangles defined used world coordinate vertices
		updateWorldPositions();
		//create new array of collision triangles
		if(collisionTris == null || collisionTris.Length != triangleCount)
			collisionTris = new CollisionTriangle[triangleCount];
		int faceIndex = 0;
		//create each collision triangle in this mesh
		for (int i = 0; i < indices.Length; i += 3)
			collisionTris[faceIndex++] = new CollisionTriangle(curGame, indices[i], indices[i + 1], indices[i + 2], this);
	}
}