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-rw-r--r--sly/game.scm119
1 files changed, 62 insertions, 57 deletions
diff --git a/sly/game.scm b/sly/game.scm
index 9bc3c52..1b0e0a0 100644
--- a/sly/game.scm
+++ b/sly/game.scm
@@ -30,9 +30,7 @@
#:use-module (sly math)
#:use-module (sly signal)
#:use-module (sly window)
- #:export (tick-interval
- max-ticks-per-frame
- draw-hook
+ #:export (draw-hook
start-game-loop
stop-game-loop))
@@ -40,69 +38,76 @@
;;; Game Loop
;;;
-;; Update 60 times per second by default.
-(define tick-interval (floor (/ 1000 60)))
-;; The maximum number of times the game loop will update game state in
-;; a single frame. When this upper bound is reached due to poor
-;; performance, the game will start to slow down instead of becoming
-;; completely unresponsive and possibly crashing.
-(define max-ticks-per-frame 4)
(define draw-hook (make-hook 2))
-(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 (interval rate)
+ (floor (/ 1000 rate)))
-(define (update lag)
- "Call the update callback. The update callback will be called as
-many times as tick-interval can divide LAG. The return value
-is the unused accumulator time."
- (define (iter lag ticks)
- (cond ((>= ticks max-ticks-per-frame)
- lag)
- ((>= lag tick-interval)
- (tick-agenda!)
- (iter (- lag tick-interval) (1+ ticks)))
- (else
- lag)))
- (iter lag 0))
+(define* (start-game-loop #:optional #:key
+ (frame-rate 60)
+ (tick-rate 60)
+ (max-ticks-per-frame 4))
+ "Start the game loop. FRAME-RATE specifies the optimal number of
+frames to draw per second. TICK-RATE specifies the optimal game logic
+updates per second. Both FRAME-RATE and TICK-RATE are 60 by default.
+MAX-TICKS-PER-FRAME is the maximum number of times the game loop will
+update game state in a single frame. When this upper bound is reached
+due to poor performance, the game will start to slow down instead of
+becoming completely unresponsive and possibly crashing."
+ (let ((tick-interval (interval tick-rate))
+ (frame-interval (interval frame-rate)))
+ (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 (alpha lag)
- "Calculate interpolation factor in the range [0, 1] for the
+ (define (update lag)
+ "Call the update callback. The update callback will be called as
+many times as tick-interval can divide LAG. The return value is the
+unused accumulator time."
+ (define (iter lag ticks)
+ (cond ((>= ticks max-ticks-per-frame)
+ lag)
+ ((>= lag tick-interval)
+ (tick-agenda!)
+ (iter (- lag tick-interval) (1+ ticks)))
+ (else
+ lag)))
+ (iter lag 0))
+
+ (define (alpha lag)
+ "Calculate interpolation factor in the range [0, 1] for the
leftover frame time LAG."
- (clamp 0 1 (/ lag tick-interval)))
+ (clamp 0 1 (/ lag tick-interval)))
-(define (frame-sleep time)
- "Sleep for the remainder of the frame that started at TIME."
- (let ((t (- (+ time tick-interval)
- (SDL:get-ticks))))
- (usleep (max 0 (* t 1000)))))
+ (define (frame-sleep time)
+ "Sleep for the remainder of the frame that started at TIME."
+ (let ((t (- (+ time frame-interval)
+ (SDL:get-ticks))))
+ (usleep (max 0 (* t 1000)))))
-(define (game-loop previous-time lag)
- "Update game state, and render. PREVIOUS-TIME is the time in
+ (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."
- (let* ((current-time (SDL:get-ticks))
- (dt (- current-time previous-time)))
- (process-events)
- (let ((lag (update (+ lag dt))))
- (draw dt (alpha lag))
- (frame-sleep current-time)
- (game-loop current-time lag))))
+ (let* ((current-time (SDL:get-ticks))
+ (dt (- current-time previous-time)))
+ (process-events)
+ (let ((lag (update (+ lag dt))))
+ (draw dt (alpha lag))
+ (frame-sleep current-time)
+ (game-loop current-time lag))))
-(define (start-game-loop)
- "Start the game loop."
- (call-with-prompt
- 'game-loop-prompt
- (lambda ()
- (game-loop (SDL:get-ticks) 0))
- (lambda (cont callback)
- (when (procedure? callback)
- (callback cont)))))
+ (call-with-prompt
+ 'game-loop-prompt
+ (lambda ()
+ (game-loop (SDL:get-ticks) 0))
+ (lambda (cont callback)
+ (when (procedure? callback)
+ (callback cont))))))
(define (stop-game-loop)
"Abort the game loop."