From 87fd3c3e5fafb8af0f4218308b24abb1a4ba7603 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sun, 27 Apr 2014 20:34:42 -0400
Subject: Ensure that interpolation alpha is clamped to the range [0, 1].

* 2d/game.scm (alpha):  Clamp value to [0, 1].
---
 2d/game.scm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to '2d')

diff --git a/2d/game.scm b/2d/game.scm
index ac33881..09c3c11 100644
--- a/2d/game.scm
+++ b/2d/game.scm
@@ -27,6 +27,7 @@
   #:use-module (gl)
   #:use-module (2d agenda)
   #:use-module (2d event)
+  #:use-module (2d math)
   #:use-module (2d signal)
   #:use-module (2d window)
   #:export (tick-interval
@@ -76,7 +77,7 @@ is the unused accumulator time."
 (define (alpha lag)
   "Calculate interpolation factor in the range [0, 1] for the
 leftover frame time LAG."
-  (/ lag tick-interval))
+  (clamp 0 1 (/ lag tick-interval)))
 
 (define (frame-sleep time)
   "Sleep for the remainder of the frame that started at TIME."
-- 
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