change collision API to support multi shapes

src/Collision/AABB2D.cs

@@ -77,6 +77,33 @@ namespace MoonWorks.Collision
             return new AABB2D(newCenter - newExtent, newCenter + newExtent);
 		}
 
+		public AABB2D Compose(AABB2D aabb)
+		{
+			float left = Left;
+			float top = Top;
+			float right = Right;
+			float bottom = Bottom;
+
+			if (aabb.Left < left)
+			{
+				left = aabb.Left;
+			}
+			if (aabb.Right > right)
+			{
+				right = aabb.Right;
+			}
+			if (aabb.Top < top)
+			{
+				top = aabb.Top;
+			}
+			if (aabb.Bottom > bottom)
+			{
+				bottom = aabb.Bottom;
+			}
+
+			return new AABB2D(left, top, right, bottom);
+		}
+
 		/// <summary>
 		/// Creates an AABB for an arbitrary collection of positions.
 		/// This is less efficient than defining a custom AABB method for most shapes, so avoid using this if possible.

src/Collision/ICollidable.cs

@@ -0,0 +1,12 @@
+using System.Collections.Generic;
+using MoonWorks.Math;
+
+namespace MoonWorks.Collision
+{
+    public interface ICollidable
+    {
+		IEnumerable<IShape2D> Shapes { get; }
+        AABB2D AABB { get; }
+        AABB2D TransformedAABB(Transform2D transform);
+	}
+}

src/Collision/IHasAABB2D.cs

@@ -1,16 +0,0 @@
-using MoonWorks.Math;
-
-namespace MoonWorks.Collision
-{
-	public interface IHasAABB2D
-	{
-		AABB2D AABB { get; }
-
-		/// <summary>
-		/// Returns a bounding box based on the shape.
-		/// </summary>
-		/// <param name="transform">A Transform for transforming the shape vertices.</param>
-		/// <returns>Returns a bounding box based on the shape.</returns>
-		AABB2D TransformedAABB(Transform2D transform);
-	}
-}

src/Collision/IShape2D.cs

@@ -2,7 +2,7 @@ using MoonWorks.Math;
 
 namespace MoonWorks.Collision
 {
-	public interface IShape2D : IHasAABB2D, System.IEquatable<IShape2D>
+	public interface IShape2D : ICollidable, System.IEquatable<IShape2D>
 	{
 		/// <summary>
 		/// A Minkowski support function. Gives the farthest point on the edge of a shape along the given direction.

src/Collision/NarrowPhase.cs

@@ -11,6 +11,22 @@ namespace MoonWorks.Collision
 			public int Index;
 		}
 
+        public static bool TestCollision(ICollidable collidableA, Transform2D transformA, ICollidable collidableB, Transform2D transformB)
+        {
+            foreach (var shapeA in collidableA.Shapes)
+            {
+                foreach (var shapeB in collidableB.Shapes)
+                {
+					if (TestCollision(shapeA, transformA, shapeB, transformB))
+                    {
+						return true;
+					}
+				}
+            }
+
+			return false;
+		}
+
 		public static bool TestCollision(IShape2D shapeA, Transform2D transformA, IShape2D shapeB, Transform2D transformB)
 		{
 			// If we can use a fast path check, let's do that!

src/Collision/Shapes/Circle.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using MoonWorks.Math;
 
 namespace MoonWorks.Collision
@@ -9,6 +10,13 @@ namespace MoonWorks.Collision
 	{
 		public int Radius { get; }
 		public AABB2D AABB { get; }
+		public IEnumerable<IShape2D> Shapes
+		{
+			get
+			{
+				yield return this;
+			}
+		}
 
 		public Circle(int radius)
 		{

src/Collision/Shapes/Line.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using MoonWorks.Math;
 
 namespace MoonWorks.Collision
@@ -12,7 +13,15 @@ namespace MoonWorks.Collision
 
         public AABB2D AABB { get; }
 
-        public Line(Vector2 start, Vector2 end)
+		public IEnumerable<IShape2D> Shapes
+        {
+            get
+            {
+				yield return this;
+			}
+        }
+
+		public Line(Vector2 start, Vector2 end)
         {
             Start = start;
             End = end;

src/Collision/Shapes/Point.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using MoonWorks.Math;
 
 namespace MoonWorks.Collision
@@ -9,6 +10,13 @@ namespace MoonWorks.Collision
 	public struct Point : IShape2D, System.IEquatable<Point>
 	{
 		public AABB2D AABB { get; }
+		public IEnumerable<IShape2D> Shapes
+        {
+            get
+            {
+				yield return this;
+			}
+        }
 
 		public AABB2D TransformedAABB(Transform2D transform)
 		{

src/Collision/Shapes/Rectangle.cs

@@ -1,3 +1,4 @@
+using System.Collections.Generic;
 using MoonWorks.Math;
 
 namespace MoonWorks.Collision
@@ -15,12 +16,20 @@ namespace MoonWorks.Collision
 		public int Left { get; }
 		public int Top { get; }
 		public int Bottom { get; }
-		public Vector2 BottomLeft { get; }
-		public Vector2 TopRight { get; }
+		public Vector2 TopLeft { get; }
+		public Vector2 BottomRight { get; }
 
 		public Vector2 Min { get; }
 		public Vector2 Max { get; }
 
+		public IEnumerable<IShape2D> Shapes
+        {
+            get
+            {
+				yield return this;
+			}
+        }
+
 		public Rectangle(int left, int top, int width, int height)
 		{
 			Width = width;
@@ -30,8 +39,8 @@ namespace MoonWorks.Collision
 			Top = top;
 			Bottom = top + height;
 			AABB = new AABB2D(left, top, Right, Bottom);
-			BottomLeft = new Vector2(Left, Bottom);
-			TopRight = new Vector2(Top, Right);
+			TopLeft = new Vector2(Left, Top);
+			BottomRight = new Vector2(Right, Bottom);
 			Min = AABB.Min;
 			Max = AABB.Max;
 		}

src/Collision/SpatialHash2D.cs

@@ -12,7 +12,7 @@ namespace MoonWorks.Collision
 		private readonly int cellSize;
 
 		private readonly Dictionary<long, HashSet<T>> hashDictionary = new Dictionary<long, HashSet<T>>();
-		private readonly Dictionary<T, (IHasAABB2D, Transform2D, uint)> IDLookup = new Dictionary<T, (IHasAABB2D, Transform2D, uint)>();
+		private readonly Dictionary<T, (ICollidable, Transform2D, uint)> IDLookup = new Dictionary<T, (ICollidable, Transform2D, uint)>();
 
 		public int MinX { get; private set; } = 0;
 		public int MaxX { get; private set; } = 0;
@@ -38,7 +38,7 @@ namespace MoonWorks.Collision
 		/// <param name="shape"></param>
 		/// <param name="transform2D"></param>
 		/// <param name="collisionGroups">A bitmask value specifying the groups this object belongs to.</param>
-		public void Insert(T id, IHasAABB2D shape, Transform2D transform2D, uint collisionGroups = uint.MaxValue)
+		public void Insert(T id, ICollidable shape, Transform2D transform2D, uint collisionGroups = uint.MaxValue)
 		{
 			var box = shape.TransformedAABB(transform2D);
 			var minHash = Hash(box.Min);
@@ -68,7 +68,7 @@ namespace MoonWorks.Collision
 		/// <summary>
 		/// Retrieves all the potential collisions of a shape-transform pair. Excludes any shape-transforms with the given ID.
 		/// </summary>
-		public IEnumerable<(T, IHasAABB2D, Transform2D, uint)> Retrieve(T id, IHasAABB2D shape, Transform2D transform2D, uint collisionMask = uint.MaxValue)
+		public IEnumerable<(T, ICollidable, Transform2D, uint)> Retrieve(T id, ICollidable shape, Transform2D transform2D, uint collisionMask = uint.MaxValue)
 		{
 			var returned = AcquireHashSet();
 
@@ -113,7 +113,7 @@ namespace MoonWorks.Collision
 		/// </summary>
 		/// <param name="aabb">A transformed AABB.</param>
 		/// <returns></returns>
-		public IEnumerable<(T, IHasAABB2D, Transform2D, uint)> Retrieve(AABB2D aabb, uint collisionMask = uint.MaxValue)
+		public IEnumerable<(T, ICollidable, Transform2D, uint)> Retrieve(AABB2D aabb, uint collisionMask = uint.MaxValue)
 		{
 			var returned = AcquireHashSet();
 
@@ -150,6 +150,14 @@ namespace MoonWorks.Collision
 			FreeHashSet(returned);
 		}
 
+		/// <summary>
+		/// Removes a specific ID from the SpatialHash.
+		/// </summary>
+		public void Remove(T id)
+		{
+
+		}
+
 		/// <summary>
 		/// Removes everything that has been inserted into the SpatialHash.
 		/// </summary>