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-rw-r--r--2d/game.scm59
1 files changed, 19 insertions, 40 deletions
diff --git a/2d/game.scm b/2d/game.scm
index a94a9c0..770d3b1 100644
--- a/2d/game.scm
+++ b/2d/game.scm
@@ -53,7 +53,6 @@
(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
@@ -63,9 +62,8 @@
(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))))
+ (tick-interval (floor (/ 1000 ticks-per-second))))
+ (game-loop (SDL:get-ticks) 0)))
(define (draw dt alpha)
"Render a frame."
@@ -76,48 +74,29 @@
(run-hook draw-hook dt alpha)
(SDL:gl-swap-buffers))
-(define (update)
+(define (update lag)
"Call the update callback. The update callback will be called as
-many times as `tick-interval` can divide ACCUMULATOR. The return value
+many times as tick-interval can divide LAG. 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?)
+ (if (>= lag (tick-interval))
(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))))))
+ (tick-agenda! game-agenda)
+ (update (- lag (tick-interval))))
+ lag))
+
+(define (alpha lag)
+ (/ lag (tick-interval)))
-(define (game-loop last-time)
- "Update game state, and render. LAST-TIME is the time in
-milliseconds of the last iteration of the loop."
+(define (game-loop previous-time lag)
+ "Update game state, and render. PREVIOUS-TIME is the time in
+milliseconds of the last iteration of the game loop."
(when (game-running?)
(let* ((current-time (SDL:get-ticks))
- (dt (- current-time last-time)))
- (accumulator (+ (accumulator) dt))
- (tick dt)
- (game-loop current-time))))
+ (dt (- current-time previous-time)))
+ (process-events)
+ (let ((lag (update (+ lag dt))))
+ (draw dt (alpha lag))
+ (game-loop current-time lag)))))
;;;
;;; State management