1 files changed, 55 insertions, 0 deletions
diff --git a/animation.scm b/animation.scm
new file mode 100644
index 0000000..e6627fe
--- /dev/null
+++ b/animation.scm
@@ -0,0 +1,55 @@
+(module downstroke/animation *
+  (import scheme
+          (chicken base)
+          (chicken keyword)
+          downstroke/entity
+          downstroke/world)
+
+  ;; ---- Animation data accessors ----
+
+  (define (animation-frames anim) (get-keyword #:frames anim))
+  (define (animation-duration anim) (get-keyword #:duration anim))
+
+  ;; ---- frame->tile-id ----
+  ;; Given a frames list and frame index, return the tile ID (1-indexed).
+
+  (define (frame->tile-id frames frame-idx)
+    (+ 1 (list-ref frames (modulo frame-idx (length frames)))))
+
+  ;; ---- set-animation ----
+  ;; Switch to a new animation, resetting frame and tick counters.
+  ;; No-op if the animation is already active (avoids restart mid-loop).
+
+  (define (set-animation entity name)
+    (if (eq? (entity-ref entity #:anim-name #f) name)
+        entity
+        (entity-set (entity-set (entity-set entity #:anim-name name)
+                                #:anim-frame 0)
+                    #:anim-tick 0)))
+
+  ;; ---- animate-entity ----
+  ;; Advance the animation tick/frame counter for one game tick.
+  ;; Pass the animation table for this entity's type.
+  ;; Entities without #:anim-name are returned unchanged.
+
+  (define (animate-entity entity animations)
+    (let ((anim-name (entity-ref entity #:anim-name #f)))
+      (if (not anim-name)
+          entity
+          (let* ((entry (assq anim-name animations))
+                 (anim  (and entry (cdr entry))))
+            (if (not anim)
+                entity
+                (let* ((tick     (+ 1 (entity-ref entity #:anim-tick 0)))
+                       (duration (animation-duration anim))
+                       (frames   (animation-frames anim))
+                       (frame    (entity-ref entity #:anim-frame 0)))
+                  (if (>= tick duration)
+                      (let ((new-frame (modulo (+ frame 1) (length frames))))
+                        (entity-set (entity-set (entity-set entity
+                                                            #:anim-tick 0)
+                                                #:anim-frame new-frame)
+                                    #:tile-id (frame->tile-id frames new-frame)))
+                      (entity-set (entity-set entity #:anim-tick tick)
+                                  #:tile-id (frame->tile-id frames frame)))))))))
+) ;; End of animation module