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;;; guile-2d
;;; Copyright (C) 2013, 2014 David Thompson <dthompson2@worcester.edu>
;;;
;;; This program is free software: you can redistribute it and/or
;;; modify it under the terms of the GNU General Public License as
;;; published by the Free Software Foundation, either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; This program 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
;;; General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with this program. If not, see
;;; <http://www.gnu.org/licenses/>.
;;; Commentary:
;;
;; Game data structure.
;;
;;; Code:
(define-module (2d game)
#:use-module (srfi srfi-9)
#:use-module ((sdl sdl) #:prefix SDL:)
#:use-module (figl gl)
#:use-module (2d agenda)
#:use-module (2d event)
#:use-module (2d signal)
#:use-module (2d window)
#:export (ticks-per-second
tick-interval
game-agenda
paused-agenda
draw-hook
run-game-loop
quit-game
pause-game
resume-game
game-running?
game-paused?))
;;;
;;; Game Loop
;;;
;; Possible states are:
;; * stopped
;; * running
;; * paused
(define game-loop-status (make-parameter 'stopped))
(define ticks-per-second 60)
(define tick-interval (make-parameter 0))
(define draw-hook (make-hook 2))
(define accumulator (make-parameter 0))
(define game-agenda (make-agenda))
;; This agenda is only ticked when the game loop is in the paused
;; state. Useful for things like the REPL that should be run even
;; though the game is paused.
(define paused-agenda (make-agenda))
(define (run-game-loop)
"Start the game loop."
(parameterize ((game-loop-status 'running)
(tick-interval (floor (/ 1000 ticks-per-second)))
(accumulator 0))
(game-loop (SDL:get-ticks))))
(define (draw dt alpha)
"Render a frame."
(let ((width (signal-ref window-width))
(height (signal-ref window-height)))
(gl-viewport 0 0 width height))
(gl-clear (clear-buffer-mask color-buffer depth-buffer))
(run-hook draw-hook dt alpha)
(SDL:gl-swap-buffers))
(define (update)
"Call the update callback. The update callback will be called as
many times as `tick-interval` can divide ACCUMULATOR. The return value
is the unused accumulator time."
(while (>= (accumulator) (tick-interval))
(process-events)
(tick-agenda! game-agenda)
(accumulator (- (accumulator) (tick-interval)))))
(define (alpha)
(/ (accumulator) (tick-interval)))
(define (update-and-render dt)
(update)
(draw dt (alpha)))
(define (tick dt)
"Advance the game by one frame."
(if (game-paused?)
(begin
(tick-agenda! paused-agenda)
(SDL:delay (tick-interval))
accumulator)
(catch #t
(lambda ()
(update-and-render dt))
(lambda (key . args)
(pause-game)
accumulator)
(lambda (key . args)
(display-backtrace (make-stack #t)
(current-output-port))))))
(define (game-loop last-time)
"Update game state, and render. LAST-TIME is the time in
milliseconds of the last iteration of the loop."
(when (game-running?)
(let* ((current-time (SDL:get-ticks))
(dt (- current-time last-time)))
(accumulator (+ (accumulator) dt))
(tick dt)
(game-loop current-time))))
;;;
;;; State management
;;;
(define (game-running?)
(or (eq? (game-loop-status) 'running)
(eq? (game-loop-status) 'paused)))
(define (game-paused?)
(eq? (game-loop-status) 'paused))
(define (pause-game)
"Pauses the game loop. Useful when developing."
(game-loop-status 'paused))
(define (resume-game)
"Resumes the game loop."
(when (game-paused?)
(game-loop-status 'running)))
(define (quit-game)
"Finish the current frame and terminate the game loop."
(game-loop-status 'stopped))
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