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(module downstroke-entity
*
(import scheme
(chicken base)
(only srfi-1 fold alist-delete))
;; Entities = alists with shared keys (#:type, #:x, #:y, #:width, #:height, ...).
(define (make-entity x y w h)
`((#:type . none) (#:x . ,x) (#:y . ,y) (#:width . ,w) (#:height . ,h)))
(define (entity-ref entity key #!optional default)
(cond ((assq key entity) => cdr)
((procedure? default) (default))
(else default)))
(define (entity-type entity)
(entity-ref entity #:type #f))
(define (entity-set entity key val)
(cons (cons key val) (alist-delete key entity eq?)))
(define (entity-set-many entity pairs)
(fold (lambda (pair working-ent)
(entity-set working-ent (car pair) (cdr pair)))
entity
pairs))
(define (entity-update entity key proc #!optional default)
(entity-set entity key (proc (entity-ref entity key default))))
;; #:skip-pipelines — list of symbols naming frame pipeline steps to skip for this
;; entity. Physics documents the built-in step names (see docs/physics.org). Other
;; subsystems (e.g. animation, rendering) may reserve additional symbols later and
;; use the same predicate and define-pipeline macro.
(define (entity-skips-pipeline? entity step)
(let ((skips (entity-ref entity #:skip-pipelines '())))
(and (pair? skips) (memq step skips))))
(define-syntax define-pipeline
(syntax-rules ()
((define-pipeline (identifier name) (scene entity dt) :guard guard (body ...))
(define (identifier scene entity dt)
(if (or (not guard) (entity-skips-pipeline? entity (quote name)))
entity
(body ...))))
((define-pipeline (identifier name) (scene entity dt) (body ...))
(define (identifier scene entity dt)
(if (entity-skips-pipeline? entity (quote name))
entity
(body ...))))))
) ;; End of entity
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