From 38eee24832fe6da4f135cae455881ab97953b23a Mon Sep 17 00:00:00 2001
From: Gene Pasquet <dev@etenil.net>
Date: Sat, 18 Apr 2026 02:47:10 +0100
Subject: Refresh docs and re-indent

---
 tween.scm | 406 +++++++++++++++++++++++++++++++-------------------------------
 1 file changed, 203 insertions(+), 203 deletions(-)

(limited to 'tween.scm')

diff --git a/tween.scm b/tween.scm
index 2dd0a61..4ef42ce 100644
--- a/tween.scm
+++ b/tween.scm
@@ -1,207 +1,207 @@
 (module downstroke-tween *
-  (import scheme
-          (chicken base)
-          (chicken keyword)
-          (only srfi-1 fold)
-          defstruct
-          downstroke-entity)
-
-  ;; ── Easing: t in [0,1] → eased factor in [0,1] for linear interpolation ──
-
-  (define (ease-linear t) t)
-
-  (define (ease-quad-in t) (* t t))
-
-  (define (ease-quad-out t)
-    (- 1 (* (- 1 t) (- 1 t))))
-
-  (define (ease-quad-in-out t)
-    (if (< t 0.5)
-        (* 2 t t)
-        (- 1 (* 2 (- 1 t) (- 1 t)))))
-
-  (define (ease-cubic-in t) (* t t t))
-
-  (define (ease-cubic-out t)
-    (- 1 (expt (- 1 t) 3)))
-
-  (define (ease-cubic-in-out t)
-    (if (< t 0.5)
-        (* 4 t t t)
-        (- 1.0 (/ (expt (- 2 (* 2 t)) 3) 2))))
-
-  (define (ease-sine-in-out t)
-    (- 0.5 (* 0.5 (cos (* 3.14159265358979323846 t)))))
-
-  (define (ease-expo-in t)
-    (if (zero? t) 0.0 (expt 2 (* 10 (- t 1)))))
-
-  (define (ease-expo-out t)
-    (if (>= t 1) 1.0 (- 1.0 (expt 2 (* -10 t)))))
-
-  (define (ease-expo-in-out t)
-    (cond ((<= t 0) 0.0)
-          ((>= t 1) 1.0)
-          ((< t 0.5) (/ (expt 2 (- (* 20 t) 10)) 2))
-          (else (- 1 (/ (expt 2 (+ (* -20 t) 10)) 2)))))
-
-  ;; Overshoots past 1 then settles (Robert Penner back-out, s ≈ 1.70158)
-  (define (ease-back-out t)
-    (let ((s 1.70158)
-          (u (- t 1)))
-      (+ 1 (* (+ 1 s) (expt u 3)) (* s (expt u 2)))))
-
-  ;; ── Symbol → ease procedure ───────────────────────────────────────────────
-
-  (define *ease-table*
-    `((linear . ,ease-linear)
-      (quad-in . ,ease-quad-in)
-      (quad-out . ,ease-quad-out)
-      (quad-in-out . ,ease-quad-in-out)
-      (cubic-in . ,ease-cubic-in)
-      (cubic-out . ,ease-cubic-out)
-      (cubic-in-out . ,ease-cubic-in-out)
-      (sine-in-out . ,ease-sine-in-out)
-      (expo-in . ,ease-expo-in)
-      (expo-out . ,ease-expo-out)
-      (expo-in-out . ,ease-expo-in-out)
-      (back-out . ,ease-back-out)))
-
-  (define (ease-named sym)
-    (cond ((assq sym *ease-table*) => cdr)
-          (else (error "ease-named: unknown ease symbol" sym))))
-
-  (define (ease-resolve ease)
-    (cond ((procedure? ease) ease)
-          ((symbol? ease) (ease-named ease))
-          (else (error "ease-resolve: expected symbol or procedure" ease))))
-
-  ;; ── Tween struct (internal) ───────────────────────────────────────────────
-
-  (defstruct tw
-    starts          ;; alist: (key . start-num)
-    ends            ;; alist: (key . end-num)
-    duration        ;; ms, > 0
-    delay           ;; ms, >= 0
-    ease-fn         ;; number → number
-    elapsed         ;; ms since tween started (includes delay period)
-    done?           ;; boolean
-    callback        ;; (entity → unspecified) or #f; invoked once at completion
-    repeat          ;; -1 = infinite, 0 = no more repeats, N = N repeats remaining
-    yoyo?)          ;; swap starts/ends on each repeat cycle
-
-  ;; ── Public API ────────────────────────────────────────────────────────────
-
-  (define (tween-finished? t) (tw-done? t))
-
-  (define (tween-active? t) (not (tw-done? t)))
-
-  ;; props: alist of (keyword . target-number), e.g. ((#:x . 200) (#:y . 40))
-  (define (make-tween entity #!key props (duration 500) (delay 0) (ease 'linear)
-                      (on-complete #f) (repeat 0) (yoyo? #f))
-    (unless (and (integer? duration) (> duration 0))
-      (error "make-tween: duration must be a positive integer (ms)" duration))
-    (unless (and (integer? delay) (>= delay 0))
-      (error "make-tween: delay must be a non-negative integer (ms)" delay))
-    (unless (pair? props)
-      (error "make-tween: props must be a non-empty alist" props))
-    (unless (and (integer? repeat) (>= repeat -1))
-      (error "make-tween: repeat must be -1 (infinite) or a non-negative integer" repeat))
-    (let ((ease-fn (ease-resolve ease))
-          (starts (map (lambda (p)
-                         (let ((k (car p)))
-                           (unless (keyword? k)
-                             (error "make-tween: property keys must be keywords" k))
-                           (cons k (entity-ref entity k 0))))
-                       props)))
-      (make-tw starts: starts
-               ends: props
-               duration: duration
-               delay: delay
-               ease-fn: ease-fn
-               elapsed: 0
-               done?: #f
-               callback: on-complete
-               repeat: repeat
-               yoyo?: yoyo?)))
-
-  ;; Linear interpolation with eased factor u in [0,1]
-  (define (lerp a b u)
-    (+ a (* (- b a) u)))
-
-  (define (apply-props entity starts ends u)
-    (fold (lambda (end-pair ent)
-            (let* ((k (car end-pair))
-                   (end (cdr end-pair))
-                   (start (cdr (assq k starts))))
-              (entity-set ent k (lerp start end u))))
-          entity
-          ends))
-
-  (define (tw-with-elapsed tw elapsed)
-    (make-tw starts: (tw-starts tw) ends: (tw-ends tw)
-             duration: (tw-duration tw) delay: (tw-delay tw)
-             ease-fn: (tw-ease-fn tw) elapsed: elapsed
+(import scheme
+        (chicken base)
+        (chicken keyword)
+        (only srfi-1 fold)
+        defstruct
+        downstroke-entity)
+
+;; ── Easing: t in [0,1] → eased factor in [0,1] for linear interpolation ──
+
+(define (ease-linear t) t)
+
+(define (ease-quad-in t) (* t t))
+
+(define (ease-quad-out t)
+  (- 1 (* (- 1 t) (- 1 t))))
+
+(define (ease-quad-in-out t)
+  (if (< t 0.5)
+      (* 2 t t)
+      (- 1 (* 2 (- 1 t) (- 1 t)))))
+
+(define (ease-cubic-in t) (* t t t))
+
+(define (ease-cubic-out t)
+  (- 1 (expt (- 1 t) 3)))
+
+(define (ease-cubic-in-out t)
+  (if (< t 0.5)
+      (* 4 t t t)
+      (- 1.0 (/ (expt (- 2 (* 2 t)) 3) 2))))
+
+(define (ease-sine-in-out t)
+  (- 0.5 (* 0.5 (cos (* 3.14159265358979323846 t)))))
+
+(define (ease-expo-in t)
+  (if (zero? t) 0.0 (expt 2 (* 10 (- t 1)))))
+
+(define (ease-expo-out t)
+  (if (>= t 1) 1.0 (- 1.0 (expt 2 (* -10 t)))))
+
+(define (ease-expo-in-out t)
+  (cond ((<= t 0) 0.0)
+        ((>= t 1) 1.0)
+        ((< t 0.5) (/ (expt 2 (- (* 20 t) 10)) 2))
+        (else (- 1 (/ (expt 2 (+ (* -20 t) 10)) 2)))))
+
+;; Overshoots past 1 then settles (Robert Penner back-out, s ≈ 1.70158)
+(define (ease-back-out t)
+  (let ((s 1.70158)
+        (u (- t 1)))
+    (+ 1 (* (+ 1 s) (expt u 3)) (* s (expt u 2)))))
+
+;; ── Symbol → ease procedure ───────────────────────────────────────────────
+
+(define *ease-table*
+  `((linear . ,ease-linear)
+    (quad-in . ,ease-quad-in)
+    (quad-out . ,ease-quad-out)
+    (quad-in-out . ,ease-quad-in-out)
+    (cubic-in . ,ease-cubic-in)
+    (cubic-out . ,ease-cubic-out)
+    (cubic-in-out . ,ease-cubic-in-out)
+    (sine-in-out . ,ease-sine-in-out)
+    (expo-in . ,ease-expo-in)
+    (expo-out . ,ease-expo-out)
+    (expo-in-out . ,ease-expo-in-out)
+    (back-out . ,ease-back-out)))
+
+(define (ease-named sym)
+  (cond ((assq sym *ease-table*) => cdr)
+        (else (error "ease-named: unknown ease symbol" sym))))
+
+(define (ease-resolve ease)
+  (cond ((procedure? ease) ease)
+        ((symbol? ease) (ease-named ease))
+        (else (error "ease-resolve: expected symbol or procedure" ease))))
+
+;; ── Tween struct (internal) ───────────────────────────────────────────────
+
+(defstruct tw
+  starts          ;; alist: (key . start-num)
+  ends            ;; alist: (key . end-num)
+  duration        ;; ms, > 0
+  delay           ;; ms, >= 0
+  ease-fn         ;; number → number
+  elapsed         ;; ms since tween started (includes delay period)
+  done?           ;; boolean
+  callback        ;; (entity → unspecified) or #f; invoked once at completion
+  repeat          ;; -1 = infinite, 0 = no more repeats, N = N repeats remaining
+  yoyo?)          ;; swap starts/ends on each repeat cycle
+
+;; ── Public API ────────────────────────────────────────────────────────────
+
+(define (tween-finished? t) (tw-done? t))
+
+(define (tween-active? t) (not (tw-done? t)))
+
+;; props: alist of (keyword . target-number), e.g. ((#:x . 200) (#:y . 40))
+(define (make-tween entity #!key props (duration 500) (delay 0) (ease 'linear)
+                    (on-complete #f) (repeat 0) (yoyo? #f))
+  (unless (and (integer? duration) (> duration 0))
+    (error "make-tween: duration must be a positive integer (ms)" duration))
+  (unless (and (integer? delay) (>= delay 0))
+    (error "make-tween: delay must be a non-negative integer (ms)" delay))
+  (unless (pair? props)
+    (error "make-tween: props must be a non-empty alist" props))
+  (unless (and (integer? repeat) (>= repeat -1))
+    (error "make-tween: repeat must be -1 (infinite) or a non-negative integer" repeat))
+  (let ((ease-fn (ease-resolve ease))
+        (starts (map (lambda (p)
+                       (let ((k (car p)))
+                         (unless (keyword? k)
+                           (error "make-tween: property keys must be keywords" k))
+                         (cons k (entity-ref entity k 0))))
+                     props)))
+    (make-tw starts: starts
+             ends: props
+             duration: duration
+             delay: delay
+             ease-fn: ease-fn
+             elapsed: 0
+             done?: #f
+             callback: on-complete
+             repeat: repeat
+             yoyo?: yoyo?)))
+
+;; Linear interpolation with eased factor u in [0,1]
+(define (lerp a b u)
+  (+ a (* (- b a) u)))
+
+(define (apply-props entity starts ends u)
+  (fold (lambda (end-pair ent)
+          (let* ((k (car end-pair))
+                 (end (cdr end-pair))
+                 (start (cdr (assq k starts))))
+            (entity-set ent k (lerp start end u))))
+        entity
+        ends))
+
+(define (tw-with-elapsed tw elapsed)
+  (make-tw starts: (tw-starts tw) ends: (tw-ends tw)
+           duration: (tw-duration tw) delay: (tw-delay tw)
+           ease-fn: (tw-ease-fn tw) elapsed: elapsed
+           done?: #f callback: (tw-callback tw)
+           repeat: (tw-repeat tw) yoyo?: (tw-yoyo? tw)))
+
+(define (tw-finish tw elapsed)
+  (make-tw starts: (tw-starts tw) ends: (tw-ends tw)
+           duration: (tw-duration tw) delay: (tw-delay tw)
+           ease-fn: (tw-ease-fn tw) elapsed: elapsed
+           done?: #t callback: #f
+           repeat: 0 yoyo?: (tw-yoyo? tw)))
+
+(define (tw-next-cycle tw overflow)
+  (let* ((yoyo? (tw-yoyo? tw))
+         (starts (tw-starts tw))
+         (ends   (tw-ends tw)))
+    (make-tw starts: (if yoyo? ends starts)
+             ends:   (if yoyo? starts ends)
+             duration: (tw-duration tw) delay: 0
+             ease-fn: (tw-ease-fn tw) elapsed: overflow
              done?: #f callback: (tw-callback tw)
-             repeat: (tw-repeat tw) yoyo?: (tw-yoyo? tw)))
-
-  (define (tw-finish tw elapsed)
-    (make-tw starts: (tw-starts tw) ends: (tw-ends tw)
-             duration: (tw-duration tw) delay: (tw-delay tw)
-             ease-fn: (tw-ease-fn tw) elapsed: elapsed
-             done?: #t callback: #f
-             repeat: 0 yoyo?: (tw-yoyo? tw)))
-
-  (define (tw-next-cycle tw overflow)
-    (let* ((yoyo? (tw-yoyo? tw))
-           (starts (tw-starts tw))
-           (ends   (tw-ends tw)))
-      (make-tw starts: (if yoyo? ends starts)
-               ends:   (if yoyo? starts ends)
-               duration: (tw-duration tw) delay: 0
-               ease-fn: (tw-ease-fn tw) elapsed: overflow
-               done?: #f callback: (tw-callback tw)
-               repeat: (let ((r (tw-repeat tw))) (if (= r -1) -1 (- r 1)))
-               yoyo?: yoyo?)))
-
-  (define (tween-complete tw entity elapsed)
-    (let ((final (apply-props entity (tw-starts tw) (tw-ends tw) 1.0)))
-      (if (zero? (tw-repeat tw))
-          (begin
-            (when (tw-callback tw) ((tw-callback tw) final))
-            (values (tw-finish tw elapsed) final))
-          (let ((overflow (- (- elapsed (tw-delay tw)) (tw-duration tw))))
-            (values (tw-next-cycle tw overflow) final)))))
-
-  (define (tween-interpolate tw entity elapsed)
-    (let* ((t0    (- elapsed (tw-delay tw)))
-           (u     (min 1.0 (max 0.0 (/ t0 (tw-duration tw)))))
-           (eased ((tw-ease-fn tw) u))
-           (ent2  (apply-props entity (tw-starts tw) (tw-ends tw) eased)))
-      (if (>= u 1.0)
-          (tween-complete tw entity elapsed)
-          (values (tw-with-elapsed tw elapsed) ent2))))
-
-  (define (tween-step tw entity dt)
-    (unless (tw? tw) (error "tween-step: expected tween struct" tw))
-    (if (tw-done? tw)
-        (values tw entity)
-        (let ((elapsed (+ (tw-elapsed tw) dt)))
-          (if (< elapsed (tw-delay tw))
-              (values (tw-with-elapsed tw elapsed) entity)
-              (tween-interpolate tw entity elapsed)))))
-
-  ;; ── Pipeline step ──────────────────────────────────────────────────────────
-  ;; Auto-advance #:tween on an entity. Call from update: as part of the
-  ;; per-entity pipeline, e.g. (step-tweens entity dt). Removes #:tween
-  ;; when the tween finishes.
-
-  (define-pipeline (step-tweens tweens) (scene entity dt)
-      guard: (entity-ref entity #:tween #f)
-    (let ((tw (entity-ref entity #:tween)))
-      (receive (tw2 ent2) (tween-step tw entity dt)
-        (if (tween-finished? tw2)
-            (entity-set ent2 #:tween #f)
-            (entity-set ent2 #:tween tw2)))))
+             repeat: (let ((r (tw-repeat tw))) (if (= r -1) -1 (- r 1)))
+             yoyo?: yoyo?)))
+
+(define (tween-complete tw entity elapsed)
+  (let ((final (apply-props entity (tw-starts tw) (tw-ends tw) 1.0)))
+    (if (zero? (tw-repeat tw))
+        (begin
+          (when (tw-callback tw) ((tw-callback tw) final))
+          (values (tw-finish tw elapsed) final))
+        (let ((overflow (- (- elapsed (tw-delay tw)) (tw-duration tw))))
+          (values (tw-next-cycle tw overflow) final)))))
+
+(define (tween-interpolate tw entity elapsed)
+  (let* ((t0    (- elapsed (tw-delay tw)))
+         (u     (min 1.0 (max 0.0 (/ t0 (tw-duration tw)))))
+         (eased ((tw-ease-fn tw) u))
+         (ent2  (apply-props entity (tw-starts tw) (tw-ends tw) eased)))
+    (if (>= u 1.0)
+        (tween-complete tw entity elapsed)
+        (values (tw-with-elapsed tw elapsed) ent2))))
+
+(define (tween-step tw entity dt)
+  (unless (tw? tw) (error "tween-step: expected tween struct" tw))
+  (if (tw-done? tw)
+      (values tw entity)
+      (let ((elapsed (+ (tw-elapsed tw) dt)))
+        (if (< elapsed (tw-delay tw))
+            (values (tw-with-elapsed tw elapsed) entity)
+            (tween-interpolate tw entity elapsed)))))
+
+;; ── Pipeline step ──────────────────────────────────────────────────────────
+;; Auto-advance #:tween on an entity. Call from update: as part of the
+;; per-entity pipeline, e.g. (step-tweens entity dt). Removes #:tween
+;; when the tween finishes.
+
+(define-pipeline (step-tweens tweens) (scene entity dt)
+  guard: (entity-ref entity #:tween #f)
+  (let ((tw (entity-ref entity #:tween)))
+    (receive (tw2 ent2) (tween-step tw entity dt)
+      (if (tween-finished? tw2)
+          (entity-set ent2 #:tween #f)
+          (entity-set ent2 #:tween tw2)))))
 
 ) ;; end module
-- 
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