Improve collision demo (#612)

* Replace square in center of level with stationary ball

* Improve collision demo

- Collisions between balls are smoother.
- Fixed an issue with collision bounds not being set properly. (This is what made the collision appear unsmooth)

Source/Demos/Features/Demos/CollisionDemo.cs

@@ -36,21 +36,21 @@ namespace Features.Demos
             _blankTexture = new Texture2D(GraphicsDevice, 1, 1);
             _blankTexture.SetData(new[] { Color.WhiteSmoke });
 
-            var demoBall1 = new DemoBall(new Sprite(_spikeyBallTexture))
+            var spikyBallLeft = new DemoBall(new Sprite(_spikeyBallTexture))
             {
                 Position = new Vector2(200, 240),
                 Velocity = new Vector2(0, -120)
             };
-            _actors.Add(demoBall1);
+            _actors.Add(spikyBallLeft);
 
-            var demoBall2 = new DemoBall(new Sprite(_spikeyBallTexture))
+            var spikeyBallRight = new DemoBall(new Sprite(_spikeyBallTexture))
             {
                 Position = new Vector2(600, 240),
                 Velocity = new Vector2(0, 120)
             };
-            _actors.Add(demoBall2);
+            _actors.Add(spikeyBallRight);
 
-            var controllableBall = new DemoBall(new Sprite(_spikeyBallTexture))
+            var controllableBall = new ControllableBall(new Sprite(_spikeyBallTexture))
             {
                 Position = new Vector2(400, 240),
                 Velocity = new Vector2(0, 0)
@@ -58,26 +58,26 @@ namespace Features.Demos
             _actors.Add(controllableBall);
             _controllableBall = controllableBall;
 
-            var wall1 = new DemoWall(new Sprite(_blankTexture))
+            var topWall = new DemoWall(new Sprite(_blankTexture))
             {
                 Bounds = new RectangleF(0, 0, 800, 20),
                 Position = new Vector2(0, 0)
             };
-            _actors.Add(wall1);
+            _actors.Add(topWall);
 
-            var wall2 = new DemoWall(new Sprite(_blankTexture))
+            var bottomWall = new DemoWall(new Sprite(_blankTexture))
             {
                 Position = new Vector2(0, 460),
                 Bounds = new RectangleF(0, 0, 800, 20)
             };
-            _actors.Add(wall2);
+            _actors.Add(bottomWall);
 
-            var centerWall = new DemoWall(new Sprite(_blankTexture))
+            var spikeyBallCenter = new StationaryBall(new Sprite(_spikeyBallTexture))
             {
-                Bounds = new RectangleF(0, 0, 50, 50),
-                Position = new Vector2(400, 200)
+                Position = new Vector2(400, 240),
+                Velocity = Vector2.Zero,
             };
-            _actors.Add(centerWall);
+            _actors.Add(spikeyBallCenter);
 
             foreach (var actor in _actors)
             {
@@ -126,13 +126,6 @@ namespace Features.Demos
             foreach (var actor in _actors)
             {
                 actor.Draw(_spriteBatch);
-                if (actor.Bounds is RectangleF rect)
-                {
-                    _spriteBatch.Draw(_blankTexture, rect.ToRectangle(), Color.WhiteSmoke);
-                } else if (actor.Bounds is CircleF circle)
-                {
-                    _spriteBatch.Draw(_blankTexture, circle.Position, Color.WhiteSmoke);
-                }
             }
             _spriteBatch.End();
 
@@ -153,9 +146,10 @@ namespace Features.Demos
             Bounds = sprite.GetBoundingRectangle(new Transform2());
         }
 
-
-        public Vector2 Offset { get; set; }
-
+        /// <summary>
+        /// Gets or sets the actor's position and updates teh actor's bounds
+        /// position.
+        /// </summary>
         public Vector2 Position
         {
             get { return _position; }
@@ -166,8 +160,20 @@ namespace Features.Demos
             }
         }
 
+        /// <summary>
+        /// Gets or sets the actor's collision bounds.
+        /// </summary>
         public IShapeF Bounds { get; set; }
 
+        /// <summary>
+        /// Gets or sets how far the actor's collision bounds are offset from 
+        /// the actor's position.
+        /// </summary>
+        public Vector2 Offset { get; set; }
+
+        /// <summary>
+        /// Gets or sets the actor's velocity.
+        /// </summary>
         public Vector2 Velocity { get; set; }
 
         public virtual void OnCollision(CollisionEventArgs collisionInfo)
@@ -201,14 +207,12 @@ namespace Features.Demos
     {
         public DemoBall(Sprite sprite) : base(sprite)
         {
-            Offset = new Vector2(75, 75);
             Bounds = new CircleF(Position + Offset, 60);
         }
 
         public override void Update(GameTime gameTime)
         {
             base.Update(gameTime);
-            Bounds.Position = Position;
         }
 
         public override void OnCollision(CollisionEventArgs collisionInfo)
@@ -220,5 +224,40 @@ namespace Features.Demos
         }
     }
 
+    /// <summary>
+    /// Ball that doesn't move when collided with.
+    /// </summary>
+    class StationaryBall : DemoBall
+    {
+        public StationaryBall(Sprite sprite) : base(sprite)
+        {
+        }
+
+        public override void OnCollision(CollisionEventArgs collisionInfo)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Player controlled ball.
+    /// </summary>
+    class ControllableBall : DemoBall
+    {
+        public ControllableBall(Sprite sprite) : base(sprite)
+        {
+            Bounds = new CircleF(Position + Offset, 60);
+        }
+
+        public override void Update(GameTime gameTime)
+        {
+            base.Update(gameTime);
+        }
+
+        public override void OnCollision(CollisionEventArgs collisionInfo)
+        {
+            Position -= collisionInfo.PenetrationVector;
+        }
+    }
+
     #endregion
 }

Source/MonoGame.Extended.Collisions/QuadTree/CollisionComponent.cs

@@ -36,20 +36,13 @@ namespace MonoGame.Extended.Collisions
         /// <param name="gameTime"></param>
         public override void Update(GameTime gameTime)
         {
-            // Update bounding box locations.
-            foreach (var value in _targetDataDictionary.Values)
-            {
-                _collisionTree.Remove(value);
-                value.Bounds = value.Target.Bounds;
-                _collisionTree.Insert(value);
-            }
-
             // Detect collisions
             foreach (var value in _targetDataDictionary.Values)
             {
+                _collisionTree.Remove(value);
+
                 var target = value.Target;
-                var collisions =_collisionTree.Query(target.Bounds)
-                    .Where(data => data.Target != target);
+                var collisions =_collisionTree.Query(target.Bounds);
 
                 // Generate list of collision Infos
                 foreach (var other in collisions)
@@ -61,7 +54,9 @@ namespace MonoGame.Extended.Collisions
                     };
 
                     target.OnCollision(collisionInfo);
+                    value.Bounds = value.Target.Bounds;
                 }
+                _collisionTree.Insert(value);
             }
         }
 
@@ -156,7 +151,10 @@ namespace MonoGame.Extended.Collisions
 
         private static Vector2 PenetrationVector(CircleF circ1, CircleF circ2)
         {
-            Debug.Assert(circ1.Intersects(circ2));
+            if (!circ1.Intersects(circ2))
+            {
+                return Vector2.Zero;
+            }
 
             var displacement = Point2.Displacement(circ1.Center, circ2.Center);