Make the enemy wander around the map

egp_story/Enemy.cs

@@ -12,11 +12,15 @@ but WITHOUT ANY WARRANTY.
 */
 
 
+using System;
 using Microsoft.Xna.Framework;
 namespace egp_story
 {
 	public class Enemy : GameActor
 	{
+		private int _lastTimeMoved = 0;
+		private static Random _random = new Random( );
+
 		public Enemy( Game game, CardinalDirection initialFacingDirection, AnimatedSprite[] attackAnims,
 			AnimatedSprite[] walkAnims, AnimatedSprite[] projectileAnims )
 			: base( game, initialFacingDirection, attackAnims, walkAnims, projectileAnims )
@@ -45,11 +49,47 @@ public Enemy( Enemy other ) :
 
 		public override void Update( LevelMap levelMap, GameTime gameTime )
 		{
+			if ( ( gameTime.TotalGameTime.TotalMilliseconds - _lastTimeMoved ) > 10 ) {
+				_lastTimeMoved = ( int ) gameTime.TotalGameTime.TotalMilliseconds;
+
+				// move randomly
+				int steps = 0; // bound the maximum times to retry
+				Vector2 displacement = new Vector2( );
+				while ( steps < 10 ) {
+					displacement.X = _random.Next( 5 ) - 2;
+					displacement.Y = _random.Next( 5 ) - 2;
+
+					Rectangle newBoundingBox = BoundingBox;
+					newBoundingBox.Offset( ( int ) displacement.X, ( int ) displacement.Y );
+					if ( IsNewPositionOK( levelMap, newBoundingBox ) ) {
+						Position += displacement;
+						break;
+					}
+					else {
+						// invert the move direction
+						displacement *= -2;
+
+						newBoundingBox.Offset( ( int ) displacement.X, ( int ) displacement.Y );
+						if ( IsNewPositionOK( levelMap, newBoundingBox ) ) {
+							Position += displacement;
+							break;
+						}
+					}
+					++steps;
+				}
 
+			}
 
 			if ( CurrentAnimation != null ) {
 				CurrentAnimation.Update( gameTime );
 			}
 		}
+
+		private bool IsNewPositionOK( LevelMap levelMap, Rectangle rectangle )
+		{
+			return ( levelMap.CheckRectangleBounds( rectangle ) &&
+					!levelMap.ThePlayer.BoundingBox.Intersects( rectangle ) &&
+					CheckHitAndRemove( levelMap, rectangle, false ) == null );
+		}
 	}
 }

egp_story/GameActor.cs

@@ -131,5 +131,28 @@ public virtual void Draw( SpriteBatch spriteBatch, GameTime gameTime )
 		}
 
 		#endregion
+
+
+
+		/// <summary>
+		/// Checks if the rectangle collides with an existing game object, and if so
+		/// removes it from the map returning the removed object. Returns null if 
+		/// no collision exists.
+		/// </summary>
+		/// <param name="rectangle"></param>
+		/// <returns></returns>
+		public GameActor CheckHitAndRemove( LevelMap map, Rectangle rectangle, bool remove = true )
+		{
+			for ( int i = 0; i < map.ActorObjects.Count; ++i ) {
+				GameActor actor = map.ActorObjects[i];
+				if ( actor != this &&
+					actor.BoundingBox.Intersects( rectangle ) ) {
+					if ( remove )
+						map.ActorObjects.RemoveAt( i );
+					return actor;
+				}
+			}
+			return null;
+		}
 	}
 }

egp_story/LevelMap.cs

@@ -93,6 +93,8 @@ public bool CheckRectangleBounds( Rectangle rectangle )
 			if ( !Mask.Bounds.Contains( rectangle ) )
 				return false;
 
+			rectangle.Width--;
+			rectangle.Height--;
 			// upper left
 			Color texel = GetTexel( rectangle.Y, rectangle.X );
 			if ( texel == Color.White || texel == Color.Black ) {
@@ -117,25 +119,6 @@ public bool CheckRectangleBounds( Rectangle rectangle )
 			return false;
 		}
 
-		/// <summary>
-		/// Checks if the rectangle collides with an existing game object, and if so
-		/// removes it from the map returning the removed object. Returns null if 
-		/// no collision exists.
-		/// </summary>
-		/// <param name="rectangle"></param>
-		/// <returns></returns>
-		public GameActor CheckHitAndRemove( Rectangle rectangle )
-		{
-			for ( int i = 0; i < ActorObjects.Count; ++i ) {
-				GameActor actor = ActorObjects[i];
-				if ( actor.BoundingBox.Intersects( rectangle ) ) {
-					ActorObjects.RemoveAt( i );
-					return actor;
-				}
-			}
-			return null;
-		}
-
 		#region IUpdateable Members
 
 		public void Update( GameTime gameTime )

egp_story/Player.cs

@@ -155,7 +155,7 @@ public override void Update( LevelMap levelMap, GameTime gameTime )
 				}
 				else {
 					// check collision with other objects
-					if ( levelMap.CheckHitAndRemove( projectileBox ) != null ) {
+					if ( CheckHitAndRemove( levelMap, projectileBox ) != null ) {
 						_projectilesShot.Dequeue( );
 					}
 				}