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;;; guile-2d
;;; Copyright (C) 2013 David Thompson <dthompson2@worcester.edu>
;;;
;;; Guile-2d is free software: you can redistribute it and/or modify it
;;; under the terms of the GNU Lesser General Public License as
;;; published by the Free Software Foundation, either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; Guile-2d is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; Lesser General Public License for more details.
;;;
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Stages represent the game state at the present time.
;;
;;; Code:
(define-module (2d stage)
#:use-module (srfi srfi-9)
#:use-module (2d agenda)
#:use-module (2d scene)
#:export (make-stage
stage?
stage-agenda
stage-env
stage-scene
init-stage
enter-stage
exit-stage
draw-stage
update-stage
stage-define
stage-ref
stage-set!
current-stage
push-stage
pop-stage
replace-stage))
(define-record-type <stage>
(%make-stage agenda env scene)
stage?
(agenda stage-agenda)
(env stage-env)
(scene stage-scene))
(define (make-stage scene)
"Create a new stage object for SCENE."
(%make-stage (make-agenda) (make-hash-table) scene))
;;;
;;; Scene callbacks
;;;
(define (init-stage stage)
"Call the scene init callback for STAGE."
((scene-init (stage-scene stage))))
(define (enter-stage stage)
"Call the scene enter callback for STAGE."
((scene-enter (stage-scene stage))))
(define (exit-stage stage)
"Call the scene exit callback for STAGE."
((scene-exit (stage-scene stage))))
(define (update-stage stage)
"Call the scene update callback for STAGE."
((scene-update (stage-scene stage))))
(define (draw-stage stage)
"Call the scene draw callback for STAGE."
((scene-draw (stage-scene stage))))
;;;
;;; Stage environment
;;;
(define (%stage-define stage key value)
"Define a new variable on STAGE with the specified symbolic name KEY
and arbitrary VALUE. An error is thrown when there is already a value
associated with KEY."
(let ((env (stage-env stage)))
(if (hash-get-handle env key)
(error 'stage-already-defined-variable key)
(hash-set! env key value))))
(define (%stage-ref stage key)
"Return the value stored in STAGE associated with KEY. An error is
thrown if there is no value associated with KEY."
(let ((handle (hash-get-handle (stage-env stage) key)))
(if handle
(cdr handle)
(error 'stage-unbound-variable key))))
(define (%stage-set! stage key value)
"Associate KEY with VALUE in the STAGE environment. An error is
thrown if there is no value associated with KEY."
(let ((handle (hash-get-handle (stage-env stage) key)))
(if handle
(set-cdr! handle value)
(error 'stage-unbound-variable key))))
(define-syntax-rule (stage-define key value)
"Define the variable KEY with VALUE in the current stage
environment."
(%stage-define (current-stage) 'key value))
(define-syntax-rule (stage-ref key)
"Return the value bound to KEY in the current stage environment."
(%stage-ref (current-stage) 'key))
(define-syntax-rule (stage-set! key value)
"Assign VALUE to the variable bound to KEY in the current stage
environment."
(%stage-set! (current-stage) 'key value))
;;;
;;; Stage management
;;;
(define stack '())
(define (current-stage)
"Return the top of the stage stack or #f if the stack is empty."
(if (null? stack) #f (car stack)))
(define (push-stage stage)
"Make STAGE active and push it to the top of the stack."
(let ((prev-stage (current-stage)))
(when prev-stage
(exit-stage prev-stage))
(set! stack (cons stage stack))
(init-stage stage)
(enter-stage stage)))
(define (pop-stage)
"Replace the current stage with the next one on the stack, if
present."
(let ((prev-stage (current-stage)))
(when prev-stage
(exit-stage prev-stage))
(set! stack (cdr stack))
(when (current-stage)
(enter-stage (car stack)))))
(define (replace-stage stage)
"Replace the current stage with STAGE."
(let ((prev-stage (current-stage)))
(when prev-stage
(exit-stage prev-stage))
(set! stack (cons stage (cdr stack)))
(init-stage stage)
(enter-stage stage)))
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