Adds *Space ReindexShape (#39)

bbtree.go

@@ -320,7 +320,13 @@ func (tree *BBTree) Reindex() {
 }
 
 func (tree *BBTree) ReindexObject(obj *Shape, hashId HashValue) {
-	panic("implement me")
+	leaf := tree.leaves.Find(hashId, obj)
+	if leaf != nil {
+		if tree.LeafUpdate(leaf) {
+			tree.LeafAddPairs(leaf)
+		}
+		tree.IncrementStamp()
+	}
 }
 
 func (tree *BBTree) ReindexQuery(f SpatialIndexQuery, data interface{}) {

space.go

@@ -1129,3 +1129,15 @@ func (space *Space) ShapeQuery(shape *Shape, callback func(shape *Shape, points
 
 	return anyCollision
 }
+
+// ReindexShape re-computes the hash of the shape in both the dynamic and static list.
+func (space *Space) ReindexShape(shape *Shape) {
+
+	assert(space.locked == 0, "You cannot manually reindex objects while the space is locked. Wait until the current query or step is complete.")
+
+	shape.CacheBB()
+
+	// attempt to rehash the shape in both hashes
+	space.dynamicShapes.class.ReindexObject(shape, shape.hashid)
+	space.staticShapes.class.ReindexObject(shape, shape.hashid)
+}

space_test.go

@@ -23,3 +23,22 @@ func TestSpace_ShapeQuery(t *testing.T) {
 		t.Error("Box should be just out of range")
 	})
 }
+
+func TestSpace_ReindexShape(t *testing.T) {
+	space := NewSpace()
+	circle := space.AddShape(NewCircle(space.StaticBody, 1, Vector{}))
+	bb1 := circle.bb
+	space.ReindexShape(circle)
+	bb2 := circle.bb
+	// check unchanged
+	if got, want := bb1.String(), bb2.String(); got != want {
+		t.Errorf("got [%[1]v:%[1]T] want [%[2]v:%[2]T]", got, want)
+	}
+	circle.body.SetPosition(Vector{X: 12.0, Y: 34.0})
+	space.ReindexShape(circle)
+	bb3 := circle.bb
+	// check changed
+	if got, want := bb2.String(), bb3.String(); got == want {
+		t.Errorf("got [%[1]v:%[1]T] want [%[2]v:%[2]T]", got, want)
+	}
+}