Added function to check for collision of rectangles.

src/AnimationHelpers.elm

@@ -39,3 +39,8 @@ distanceFromSpeed pixPerSec millis =
 fmod : Float -> Float -> Float
 fmod lh rh =
     lh - (toFloat (floor (lh / rh)) * rh)
+
+
+rectToRectCollision : ( Point, Point ) -> ( Point, Point ) -> Bool
+rectToRectCollision ( ( ax1, ay1 ), ( ax2, ay2 ) ) ( ( bx1, by1 ), ( bx2, by2 ) ) =
+    ax1 < bx2 && ax2 > bx1 && ay1 < by2 && ay2 > by1

tests/Tests.elm

@@ -2,7 +2,14 @@ module Tests exposing (..)
 
 import Test exposing (..)
 import Expect
-import AnimationHelpers exposing (calculateAnimation, movePosition, distanceFromSpeed, fmod)
+import AnimationHelpers
+    exposing
+        ( calculateAnimation
+        , movePosition
+        , distanceFromSpeed
+        , fmod
+        , rectToRectCollision
+        )
 
 
 trimFloatX : Int -> Float -> Float
@@ -107,4 +114,18 @@ all =
                         (fmod 51934 123)
                         28
             ]
+        , describe "Rectangle collision testing"
+            [ test "No collision" <|
+                \() ->
+                    Expect.false "Expect rectangles not to collide" <|
+                        rectToRectCollision
+                            ( ( 10, 10 ), ( 20, 30 ) )
+                            ( ( 30, 50 ), ( 40, 60 ) )
+            , test "Collide left" <|
+                \() ->
+                    Expect.true "Expect rectangles to collide" <|
+                        rectToRectCollision
+                            ( ( 30, 10 ), ( 50, 30 ) )
+                            ( ( 10, 10 ), ( 40, 30 ) )
+            ]
         ]