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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) (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))))
;; er-macro-transformer so (rename 'entity-skips-pipeline?) captures the
;; binding from THIS module — works across compiled unit boundaries.
;;
;; Syntax:
;; (define-pipeline (name skip-sym) (entity-formal ...)
;; guard: guard-expr ;; optional — entity returned unchanged when #f
;; body ...)
(define-syntax define-pipeline
(er-macro-transformer
(lambda (form rename _compare)
(let* ((name-skip (cadr form))
(name (car name-skip))
(skip (cadr name-skip))
(formals (caddr form))
(f1 (car formals))
(rest (cdddr form))
(has-guard? (and (pair? rest) (pair? (cdr rest))
(eq? (car rest) guard:)))
(guard-expr (and has-guard? (cadr rest)))
(body (if has-guard? (cddr rest) rest))
(%define (rename 'define))
(%if (rename 'if))
(%let (rename 'let))
(%not (rename 'not))
(%quote (rename 'quote))
(%skip? (rename 'entity-skips-pipeline?)))
(if has-guard?
`(,%define (,name ,@formals)
(,%if (,%skip? ,f1 (,%quote ,skip))
,f1
(,%if (,%not ,guard-expr)
,f1
(,%let () ,@body))))
`(,%define (,name ,@formals)
(,%if (,%skip? ,f1 (,%quote ,skip))
,f1
(,%let () ,@body))))))))
) ;; End of entity
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