From ea4100bd02143fea255cc0441cbeeb842796a58a Mon Sep 17 00:00:00 2001
From: 3gg <3gg@shellblade.net>
Date: Mon, 18 Nov 2024 17:42:20 -0800
Subject: Fix momentum.

---
 Demos/Pong/Pong.hs | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/Demos/Pong/Pong.hs b/Demos/Pong/Pong.hs
index dd8855b..b9661ee 100644
--- a/Demos/Pong/Pong.hs
+++ b/Demos/Pong/Pong.hs
@@ -31,7 +31,7 @@ initialBallVelocity = vec2 1 1
 maxBounceAngle      = (65::Float) * (pi::Float)/(180::Float)
 playerSpeed         = 1.0 :: Float
 enemySpeed          = 7.0 :: Float
-enemyMomentum       = 0.1 :: Float
+enemyMomentum       = 1.0 :: Float
 initialEnemyPos     = vec2 0.5 0.9
 initialPlayerPos    = vec2 0.5 0.1
 initialBallPos      = vec2 0.5 0.5
@@ -150,13 +150,13 @@ moveBall = step $ \_ dt _ _ (vel, ball) -> (translate (vel * dt) ball, moveBall)
 stepEnemy = movePad 0 .> clamp
 
 movePad :: Float -> Step [GameObject] e GameObject GameObject
-movePad previousMomentum = step $ \_ dt gos _ pad ->
-  let ball        = head gos
-      offset      = (x . position $ ball) - (x . position $ pad)
-      chaseVector = enemySpeed * offset
-      momentum    = previousMomentum + enemyMomentum * chaseVector
-      vx          = chaseVector + momentum
-   in (translate (vec2 (vx * dt) 0) pad, movePad momentum)
+movePad previousMomentumVector = step $ \_ dt gos _ pad ->
+  let ball           = head gos
+      heading        = (x . position $ ball) - (x . position $ pad)
+      chaseVector    = enemySpeed * heading
+      momentumVector = previousMomentumVector + enemyMomentum * heading * dt
+      vx             = chaseVector * dt + momentumVector
+   in (translate (vec2 vx 0) pad, movePad momentumVector)
 
 sign :: Float -> Float
 sign x = if x >= 0 then 1 else -1
-- 
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