diff options
| -rw-r--r-- | 2d/game.scm | 59 |
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 |