MonoGame.Samples/BookSourceCode/XNAGameDevelopmentbyExampleCode/AsteroidBeltAssault/Enemy.cs

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

namespace Asteroid_Belt_Assault
{
    class Enemy
    {
        public Sprite EnemySprite;
        public Vector2 gunOffset = new Vector2(25, 25);
        private Queue<Vector2> waypoints = new Queue<Vector2>();
        private Vector2 currentWaypoint = Vector2.Zero;
        private float speed = 120f;
        public bool Destroyed = false;
        private int enemyRadius = 15;
        private Vector2 previousLocation = Vector2.Zero;

        public Enemy(
            Texture2D texture,
            Vector2 location,
            Rectangle initialFrame,
            int frameCount)
        {
            EnemySprite = new Sprite(
                location,
                texture,
                initialFrame,
                Vector2.Zero);

            for (int x = 1; x < frameCount; x++)
            {
                EnemySprite.AddFrame(
                    new Rectangle(
                    initialFrame.X = (initialFrame.Width * x),
                    initialFrame.Y,
                    initialFrame.Width,
                    initialFrame.Height));
            }
            previousLocation = location;
            currentWaypoint = location;
            EnemySprite.CollisionRadius = enemyRadius;
        }

        public void AddWaypoint(Vector2 waypoint)
        {
            waypoints.Enqueue(waypoint);
        }

        public bool WaypointReached()
        {
            if (Vector2.Distance(EnemySprite.Location, currentWaypoint) <
                (float)EnemySprite.Source.Width / 2)
            {
                return true;
            }
            else
            {
                return false;
            }
        }

        public bool IsActive()
        {
            if (Destroyed)
            {
                return false;
            }

            if (waypoints.Count > 0)
            {
                return true;
            }

            if (WaypointReached())
            {
                return false;
            }

            return true;
        }

        public void Update(GameTime gameTime)
        {
            if (IsActive())
            {
                Vector2 heading = currentWaypoint - EnemySprite.Location;
                if (heading != Vector2.Zero)
                {
                    heading.Normalize();
                }
                heading *= speed;
                EnemySprite.Velocity = heading;
                previousLocation = EnemySprite.Location;
                EnemySprite.Update(gameTime);
                EnemySprite.Rotation =
                    (float)Math.Atan2(
                    EnemySprite.Location.Y - previousLocation.Y,
                    EnemySprite.Location.X - previousLocation.X);

                if (WaypointReached())
                {
                    if (waypoints.Count > 0)
                    {
                        currentWaypoint = waypoints.Dequeue();
                    }
                }
            }
        }

        public void Draw(SpriteBatch spriteBatch)
        {
            if (IsActive())
            {
                EnemySprite.Draw(spriteBatch);
            }
        }


    }
}