adds documentation for AABB and revised IShape2D

content/api/AABB.md

@@ -0,0 +1,27 @@
+---
+title: "AABB"
+date: 2019-12-31T14:36:00-07:00
+weight: 6
+---
+
+*AABB*, or axis-aligned bounding box, is defined by a minimum point and a maximum point. It is used for broad-phase collision detection. It represents a rectangular outline of the shape so we can quickly insert shapes into a *SpatialHash*.
+
+## Properties
+
+##### **public Vector2 Min { get; private set; }**
+
+The minimum point of the AABB.
+
+##### **public Vector2 Max { get; private set; }**
+
+The maximum point of the AABB.
+
+## Methods
+
+##### **public static AABB FromVertices(IEnumerable<Position2D> vertices)**
+
+Can be used to generate an AABB from an arbitrary collection of vertices. It is generally better to define a more efficient AABB generation method based on the properties of a particular shape, but this can be used for an arbitrary collection of vertices, like a polygon.
+
+##### **public static AABB Transformed(AABB aabb, Transform2D transform)**
+
+Efficiently transforms an AABB. Used internally by SpatialHash to quickly transform a shape's AABB.

content/api/IShape2D.md

@@ -8,6 +8,12 @@ An *IShape2D* is an interface that, when implemented, allows for spatial hashing
 
 Your *IShape2D* implementations should be structs for memory efficiency purposes.
 
+## Properties
+
+##### **public AABB { get; }**
+
+An axis-aligned bounding box for the shape. This is stored so we can efficiently transform the AABB when necessary.
+
 ## Methods
 
 ##### **Vector2 Support(Vector2 direction, Transform2D transform)**
@@ -34,13 +40,8 @@ A method which returns the axis-aligned bounding box for the transformed shape.
 For example, the AABB method for Bonk's *Circle* implementation:
 
 ```cs
-public AABB AABB(Transform2D Transform2D)
+public AABB TransformedAABB(Transform2D Transform2D)
 {
-    return new AABB(
-        Transform2D.Position.X - Radius,
-        Transform2D.Position.Y - Radius,
-        Transform2D.Position.X + Radius,
-        Transform2D.Position.Y + Radius
-    );
+    return AABB.Transformed(AABB, transform2D);
 }
 ```