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+;;; guile-2d
+;;; Copyright (C) 2013 David Thompson <dthompson2@worcester.edu>
+;;;
+;;; Guile-2d is free software: you can redistribute it and/or modify it
+;;; under the terms of the GNU Lesser General Public License as
+;;; published by the Free Software Foundation, either version 3 of the
+;;; License, or (at your option) any later version.
+;;;
+;;; Guile-2d 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
+;;; Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public
+;;; License along with this program.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; Frames per second counter.
+;;
+;;; Code:
+
+(define-module (2d fps)
+  #:use-module (2d game)
+  #:export (fps))
+
+;; Current frames per second
+(define fps (make-parameter 0))
+
+(define accumulate-fps!
+  (let* ((elapsed-time 0)
+         (fps-counter 0))
+    (lambda (dt alpha)
+      "Increment the frames-per-second counter. Resets to 0 every
+second."
+      (let ((new-time (+ elapsed-time dt))
+            (new-fps (1+ fps-counter)))
+        (if (>= new-time 1000)
+            (begin
+              (fps new-fps)
+              (set! fps-counter 0)
+              (set! elapsed-time 0))
+            (begin
+              (set! fps-counter new-fps)
+              (set! elapsed-time new-time)))))))
+
+(add-hook! draw-hook accumulate-fps!)