From 797b616c66ab514880cf5a4fd8cb6837b43b52a1 Mon Sep 17 00:00:00 2001
From: Thomas White <taw@physics.org>
Date: Sun, 30 Oct 2022 21:58:27 +0100
Subject: Add flash-chase

---
 guile/starlet/effects.scm | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/guile/starlet/effects.scm b/guile/starlet/effects.scm
index c14f5a0..b6bfd2a 100644
--- a/guile/starlet/effects.scm
+++ b/guile/starlet/effects.scm
@@ -20,8 +20,10 @@
 ;;
 (define-module (starlet effects)
   #:use-module (starlet clock)
+  #:use-module (starlet state)
   #:export (flash
-             sinewave))
+             sinewave
+             flash-chase))
 
 
 (define pi (* 2 (acos 0)))
@@ -45,3 +47,25 @@
       (+ range-min
          (* (/ (- range-max range-min) 2)
             (+ 1 (sin (* 2 pi hz (elapsed-time clock)))))))))
+
+
+(define (hump t on-time)
+  (cond
+    ((< t 0.0) 0.0)
+    ((> t on-time) 0.0)
+    (else (* 100 (sin (* pi (/ t on-time)))))))
+
+
+(define* (flash-chase group
+                      #:key (repeat-time 2) (offset-time 0.3) (on-time 0.5))
+  (let ((clock (make-clock)))
+    (for-each
+      (lambda (fix idx)
+        (at fix 'intensity
+            (lambda ()
+              (hump (- (euclidean-remainder (elapsed-time clock)
+                                            repeat-time)
+                       (* idx offset-time))
+                    on-time))))
+      group
+      (iota (length group)))))
-- 
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