1 files changed, 37 insertions, 22 deletions

diff --git a/Demos/Pong/Pong.hs b/Demos/Pong/Pong.hs
index fd7fbeb..0e24a42 100644
--- a/Demos/Pong/Pong.hs
+++ b/Demos/Pong/Pong.hs
@@ -16,18 +16,15 @@ import           Spear.Step
 
 -- Configuration
 
-padSize = vec2 0.05 0.02
-
-ballSize = 0.01
-
-ballVelocity = vec2 0.3 0.3
-
-playerSpeed = 0.7
-
+padSize = vec2 0.07 0.02
+ballSize = 0.012
+ballSpeed = 0.6
+initialBallVelocity = vec2 1 1
+maxBounceAngle = 65 * pi/180
+playerSpeed = 1.0
+enemySpeed = 1.5
 initialEnemyPos = vec2 0.5 0.9
-
 initialPlayerPos = vec2 0.5 0.1
-
 initialBallPos = vec2 0.5 0.5
 
 -- Game events
@@ -66,7 +63,7 @@ padBox = AABB2 (-padSize) padSize
 obj2 = obj2FromVectors unitx2 unity2
 
 newWorld =
-  [ GameObject ballBox (obj2 initialBallPos) $ stepBall ballVelocity,
+  [ GameObject ballBox (obj2 initialBallPos) $ stepBall initialBallVelocity,
     GameObject padBox (obj2 initialEnemyPos) stepEnemy,
     GameObject padBox (obj2 initialPlayerPos) stepPlayer
   ]
@@ -75,19 +72,37 @@ newWorld =
 
 stepBall vel = collideBall vel .> moveBall
 
+-- TODO: in collideBall and paddleBounce, we should an apply an offset to the
+-- ball when collision is detected.
 collideBall :: Vector2 -> Step [GameObject] e GameObject (Vector2, GameObject)
 collideBall vel = step $ \_ dt gos _ ball ->
   let (AABB2 pmin pmax) = aabb ball `aabbAdd` pos ball
-      collideCol = x pmin < 0 || x pmax > 1
-      collideRow = y pmin < 0 || y pmax > 1 || any (collide ball) (tail gos)
-      negx v@(Vector2 x y) = if collideCol then vec2 (-x) y else v
-      negy v@(Vector2 x y) = if collideRow then vec2 x (-y) else v
-      vel' = negx . negy $ vel
-      delta = dt -- A small delta to apply when collision occurs.
-      adjustX = if collideCol then scale delta (vec2 (x vel) 0) else vec2 0 0
-      adjustY = if collideRow then scale delta (vec2 0 (y vel)) else vec2 0 0
-   in ((vel' + adjustX + adjustY, ball), collideBall vel')
-
+      collideSide = x pmin < 0 || x pmax > 1
+      collideBack = y pmin < 0 || y pmax > 1
+      collidePaddle = any (collide ball) (tail gos)
+      flipX v@(Vector2 x y) = if collideSide then vec2 (-x) y else v
+      flipY v@(Vector2 x y) = if collideBack then vec2 x (-y) else v
+      vel' = normalise . (\v -> foldl (paddleBounce ball) v (tail gos)) . flipX . flipY $ vel
+      -- A small delta to apply when collision occurs.
+      delta = 1 + if collideSide || collideBack || collidePaddle then 2*dt else 0
+   in ((scale ballSpeed (scale delta vel'), ball), collideBall vel')
+
+paddleBounce :: GameObject -> Vector2 -> GameObject -> Vector2
+paddleBounce ball v paddle =
+  if collide ball paddle
+  then
+    let (AABB2 pmin pmax) = aabb paddle `aabbAdd` pos paddle
+        center = (x pmin + x pmax) / 2
+        -- Normalized offset of the ball from the paddle's center, [-1, +1].
+        -- It's outside the [-1, +1] range if there is no collision.
+        offset = (x (pos ball) - center) / ((x pmax - x pmin) / 2)
+        angle  = offset * maxBounceAngle
+        -- When it bounces off of a paddle, y vel is flipped.
+        ysign = -(signum (y v))
+    in vec2 (sin angle) (ysign * cos angle)
+  else v
+
+collide :: GameObject -> GameObject -> Bool
 collide go1 go2 =
   let (AABB2 (Vector2 xmin1 ymin1) (Vector2 xmax1 ymax1)) =
         aabb go1 `aabbAdd` pos go1
@@ -112,7 +127,7 @@ movePad :: Step s e GameObject GameObject
 movePad = step $ \elapsed _ _ _ pad ->
   let p = vec2 px 0.9
       px =
-        double2Float (sin elapsed * 0.5 + 0.5)
+        double2Float (sin (elapsed * enemySpeed) * 0.5 + 0.5)
           * (1 - 2 * x padSize)
           + x padSize
    in (setPos p pad, movePad)