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(module downstroke-entity
*
(import scheme
(chicken base)
(chicken keyword)
(only srfi-1 fold))
;; Entities = plists with shared keys (#:type, #:x, #:y, #:width, #:height, ...).
(define (make-entity x y w h)
(list #:type 'none #:x x #:y y #:width w #:height h))
(define (entity-ref entity key #!optional default)
(get-keyword key entity (if (procedure? default) default (lambda () default))))
(define (entity-type entity)
(entity-ref entity #:type #f))
(define (entity-set entity key val)
(let ((cleaned (let loop ((lst entity) (acc '()))
(if (null? lst)
(reverse acc)
(let ((k (car lst))
(v (cadr lst)))
(if (eq? k key)
(loop (cddr lst) acc)
(loop (cddr lst) (cons v (cons k acc)))))))))
(cons key (cons val cleaned))))
(define (entity-set-many entity pairs)
(fold (lambda (pair working-ent)
(entity-set working-ent (car pair) (if (list? (cdr pair)) (cadr 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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