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(module (downstroke animation) *
(import scheme
(chicken base)
(only srfi-1 filter)
(downstroke entity)
(downstroke world))
;; Animation definitions are alists (converted from plist form in the user's
;; prefab data file by load-prefabs). Each animation is an alist with keys
;; #:name, #:frames, optional #:duration.
;; Look up a key in an animation alist. Mirrors entity-ref:
;; a non-procedure default is returned as-is on miss; a procedure default
;; is invoked as a thunk.
(define (animation-ref anim key #!optional default)
(cond ((assq key anim) => cdr)
((procedure? default) (default))
(else default)))
(define (animation-frames anim) (animation-ref anim #:frames))
(define (animation-duration anim) (animation-ref anim #:duration))
(define (frame-by-idx frames frame-idx)
(list-ref frames (modulo frame-idx (length frames))))
;; The tile ID is 1-indexed.
(define (frame->tile-id frames frame-idx)
(let ((frame-def (frame-by-idx frames frame-idx)))
(if (list? frame-def)
(car frame-def)
frame-def)))
(define (frame->duration frames frame-idx)
(let ((frame-def (frame-by-idx frames frame-idx)))
(if (list? frame-def)
(cadr frame-def)
10)))
;; ---- 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)))
(define (animation-by-name animations name)
(let ((matching-anims
(filter (lambda (anim) (eq? (animation-ref anim #:name) name))
animations)))
(if (pair? matching-anims)
(car matching-anims)
#f)))
;; ---- 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 (advance-animation entity anim)
(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-id (modulo (+ frame 1) (length frames))))
(entity-set-many entity
`((#:anim-tick . 0)
(#:anim-frame . ,new-frame-id)
(#:tile-id . ,(frame->tile-id frames new-frame-id))
(#:duration . ,(frame->duration frames new-frame-id)))))
(entity-set-many entity
`((#:anim-tick . ,tick)
(#:tile-id . ,(frame->tile-id frames frame)))))))
(define (animate-entity entity animations)
(let* ((anim-name (entity-ref entity #:anim-name #f))
(anim (and anim-name (animation-by-name animations anim-name))))
(if anim
(advance-animation entity anim)
entity)))
(define-pipeline (apply-animation animation) (scene entity dt)
guard: (entity-ref entity #:animations #f)
(let ((animations (entity-ref entity #:animations #f)))
(animate-entity entity animations)))
) ;; End of animation module
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