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refactor(galaga): fix multiple swap! calls per Erik's feedback
Apply Erik's atomic state update pattern to Galaga game, fixing 3 instances of multiple swap! calls that could cause race conditions and unnecessary re-renders. Fixes: 1. Bullet-Enemy Collision: Combined 5 separate swap! calls into single atomic update (bullets, enemies, score, particles) 2. Enemy Bullet-Player Collision: Combined 5 separate swap! calls into single atomic update (bullets, lives, particles, game status, high score) 3. Formation Movement: Eliminated nested swap! inside swap! function, replaced with single swap! using cond logic for direction changes Benefits: - No race conditions in multi-threaded environments - Single Reagent re-render per game event instead of multiple - Cleaner code using threading macros - Predictable atomic state updates - Follows functional programming best practices Pattern used: Single swap! with update function and threading (->) for all related state changes, with conditional logic for optional updates.
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Lines changed: 77 additions & 47 deletions

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‎src/scittle/games/galaga.cljs‎

Lines changed: 77 additions & 47 deletions
Original file line numberDiff line numberDiff line change
@@ -322,18 +322,25 @@
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(assoc star :y new-y))))
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stars))))
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;; Update formation movement (side-to-side only, no descent)
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(let [direction (:formation-direction @game-state)]
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(swap! game-state update :formation-offset
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(fn [{:keys [x y]}]
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(let [new-x (+ x (* direction 0.5))]
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(cond
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(and (>= new-x 30) (= direction 1))
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(do (swap! game-state assoc :formation-direction -1)
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{:x 30 :y y}) ; Keep y the same - no descent!
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(and (<= new-x -30) (= direction -1))
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(do (swap! game-state assoc :formation-direction 1)
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{:x -30 :y y}) ; Keep y the same - no descent!
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:else {:x new-x :y y})))))
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(let [direction (:formation-direction @game-state)
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offset (:formation-offset @game-state)
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x (:x offset)
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y (:y offset)
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new-x (+ x (* direction 0.5))]
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;; Single atomic update for formation movement and direction changes
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(swap! game-state
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(fn [state]
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(cond
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(and (>= new-x 30) (= direction 1))
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(-> state
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(assoc :formation-direction -1)
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(assoc :formation-offset {:x 30 :y y}))
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(and (<= new-x -30) (= direction -1))
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(-> state
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(assoc :formation-direction 1)
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(assoc :formation-offset {:x -30 :y y}))
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:else
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(assoc state :formation-offset {:x new-x :y y})))))
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;; Update enemies
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(swap! game-state update :enemies
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(fn [enemies]
@@ -380,45 +387,68 @@
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enemy enemies]
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(when (and (collides? :a bullet :b enemy)
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(not= (:state enemy) :destroyed))
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;; Remove bullet
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(swap! game-state update :bullets
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#(vec (remove (fn [b] (= b bullet)) %)))
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;; Damage enemy
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(let [new-hits (dec (:hits enemy))]
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(if (<= new-hits 0)
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;; Destroy enemy
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(do
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(play-explosion-sound) ; Play explosion sound
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(swap! game-state update :enemies
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#(vec (remove (fn [e] (= e enemy)) %)))
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(swap! game-state update :score + (:points enemy))
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(swap! game-state update :particles
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#(vec (concat % (create-particles :x (:x enemy)
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:y (:y enemy)
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:count 10
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:color (:color enemy))))))
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;; Damage enemy
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(swap! game-state update :enemies
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#(mapv (fn [e]
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(if (= e enemy)
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(assoc e :hits new-hits)
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e))
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%))))))
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(let [new-hits (dec (:hits enemy))
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destroyed? (<= new-hits 0)]
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(when destroyed?
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(play-explosion-sound)) ; Play explosion sound
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;; Single atomic update for all collision effects
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(swap! game-state
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(fn [state]
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(-> state
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;; Remove bullet
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(update :bullets #(vec (remove (fn [b] (= b bullet)) %)))
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;; Handle enemy destruction or damage
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(update :enemies
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(fn [enemies]
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(if destroyed?
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;; Destroy enemy
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(vec (remove (fn [e] (= e enemy)) enemies))
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;; Damage enemy
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(mapv (fn [e]
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(if (= e enemy)
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(assoc e :hits new-hits)
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e))
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enemies))))
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;; Add score if destroyed
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(#(if destroyed?
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(update % :score + (:points enemy))
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%))
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;; Add particles if destroyed
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(#(if destroyed?
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(update % :particles
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(fn [particles]
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(vec (concat particles
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(create-particles :x (:x enemy)
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:y (:y enemy)
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:count 10
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:color (:color enemy))))))
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%))))))))
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;; Check enemy bullet-player collisions
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(doseq [bullet enemy-bullets]
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(when (collides? :a bullet :b player)
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(play-hit-sound) ; Play hit sound
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(swap! game-state update :enemy-bullets
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#(vec (remove (fn [b] (= b bullet)) %)))
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(swap! game-state update-in [:player :lives] dec)
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(swap! game-state update :particles
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#(vec (concat % (create-particles :x (:x player)
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:y (:y player)
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:count 15
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:color "#FFFF00"))))
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(when (<= (get-in @game-state [:player :lives]) 0)
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(swap! game-state assoc :game-status :game-over)
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(swap! game-state update :high-score max (:score @game-state)))))
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;; Single atomic update for all hit effects
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(let [new-lives (dec (:lives player))
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game-over? (<= new-lives 0)]
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(swap! game-state
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(fn [state]
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(-> state
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;; Remove bullet
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(update :enemy-bullets #(vec (remove (fn [b] (= b bullet)) %)))
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;; Decrement lives
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(update-in [:player :lives] dec)
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;; Add particles
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(update :particles
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#(vec (concat % (create-particles :x (:x player)
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:y (:y player)
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:count 15
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:color "#FFFF00"))))
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;; If game over, update status and high score
447+
(#(if game-over?
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(-> %
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(assoc :game-status :game-over)
450+
(update :high-score max (:score %)))
451+
%))))))))
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;; Check for wave clear
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(when (empty? enemies)
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(play-wave-complete-sound) ; Play victory sound

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