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-rw-r--r--2d/game.scm9
1 files changed, 9 insertions, 0 deletions
diff --git a/2d/game.scm b/2d/game.scm
index 7f24193..14543e8 100644
--- a/2d/game.scm
+++ b/2d/game.scm
@@ -76,8 +76,16 @@ is the unused accumulator time."
lag))
(define (alpha lag)
+ "Calculate interpolation factor in the range [0, 1] for the
+leftover frame time LAG."
(/ 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 (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."
@@ -86,6 +94,7 @@ milliseconds of the last iteration of the game loop."
(process-events)
(let ((lag (update (+ lag dt))))
(draw dt (alpha lag))
+ (frame-sleep current-time)
(game-loop current-time lag))))
(define (quit-game)