From 3027010b87e30bc1546ff48b9e5011fa3b3e8fb6 Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Sun, 18 Sep 2022 17:47:37 -0700
Subject: Slightly better collision handling.

---
 demos/pong/Pong.hs | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/demos/pong/Pong.hs b/demos/pong/Pong.hs
index 906e89b..accc75d 100644
--- a/demos/pong/Pong.hs
+++ b/demos/pong/Pong.hs
@@ -76,16 +76,17 @@ newWorld =
 stepBall vel = collideBall vel .> moveBall
 
 collideBall :: Vector2 -> Step [GameObject] e GameObject (Vector2, GameObject)
-collideBall vel = step $ \_ _ gos _ ball ->
+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)
+      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
-   in ((vel', ball), collideBall 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')
 
 collide go1 go2 =
   let (AABB2 (Vector2 xmin1 ymin1) (Vector2 xmax1 ymax1)) =
-- 
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