sneak/Shared/NPC.cs

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

namespace SemiColinGames {
  class IdleState : IState<NPC> {
    float timeInState = 0;

    public void Enter() {
      timeInState = 0;
    }

    public string Update(NPC npc, float modelTime, World world) {
      timeInState += modelTime;
      if (timeInState > 1.0f) {
        npc.Facing *= -1;
        return "run";
      }
      return null;
    }
  }

  class RunState : IState<NPC> {
    public void Enter() {}

    public string Update(NPC npc, float modelTime, World world) {
      int moveSpeed = 120;
      int desiredX = npc.Position.X + (int) (moveSpeed * npc.Facing * modelTime);
      int testPoint = desiredX + 12 * npc.Facing;
      // TODO: define the box modularly & correctly.
      AABB npcBox = new AABB(new Vector2(testPoint, npc.Position.Y), new Vector2(1, 25));
      Debug.AddRect(npcBox, Color.Cyan);
      bool foundBox = false;
      foreach (AABB box in world.CollisionTargets) {
        if (box.Intersect(npcBox) != null) {
          foundBox = true;
          break;
        }
      }

      if (!foundBox) {
        return "idle";
      }
      npc.Position.X = desiredX;
      return null;
    }
  }

  public class NPC {
    private readonly Sprite sprite;
    private readonly Vector2 spriteCenter;
    private readonly Vector2 eyeOffset = new Vector2(4, -9);

    private readonly FSM<NPC> fsm;
    private AABB physicsBox;
    private readonly Vector2 halfSize = new Vector2(12, 24);

    public NPC(Point position, int facing) {
      sprite = Sprites.Executioner;
      Position = position;
      spriteCenter = new Vector2(
          sprite.Width / 2, sprite.Height - halfSize.Y - sprite.GroundPadding);
      physicsBox = new AABB(position.ToVector2(), halfSize);
      Facing = facing;
      fsm = new FSM<NPC>(new Dictionary<string, IState<NPC>> {
        { "idle", new IdleState() },
        { "run", new RunState() }
      }, "run");
    }

    public int Facing;
    public Point Position;

    public Vector2 EyePosition {
      get {
        return Vector2.Add(
            Position.ToVector2(), new Vector2(eyeOffset.X * Facing, eyeOffset.Y));
      }
    }

    public float VisionRange {
      get {
        return 150;
      }
    }

    public float FieldOfView {
      get {
        return FMath.DegToRad(120);
      }
    }

    public Vector2 VisionRay {
      get {
        return new Vector2(VisionRange * Facing, 0);
      }
    }

    public void Update(float modelTime, World world) {
      fsm.Update(this, modelTime, world);
      physicsBox = new AABB(Position.ToVector2(), halfSize);
      Debug.AddRect(physicsBox, Color.White);
    }

    public void Draw(SpriteBatch spriteBatch) {
      Rectangle textureSource =
          sprite.GetTextureSource(fsm.StateName, Clock.ModelTime.TotalSeconds);
      SpriteEffects effect = Facing == 1 ?
        SpriteEffects.None : SpriteEffects.FlipHorizontally;
      Color color = Color.White;
      spriteBatch.Draw(Textures.Executioner.Get, Position.ToVector2(), textureSource, color, 0f,
        spriteCenter, Vector2.One, effect, 0f);
    }
  }
}