From 95197eb073035de7ae30cb76d9783b4d1dc6b45a Mon Sep 17 00:00:00 2001
From: Thomas White <taw@physics.org>
Date: Sat, 15 May 2021 18:10:51 +0200
Subject: Add clock module

This will be the basis for a simplification of how cue fade times are
handled, making it possible to implement "stop" and "back" operations
for playbacks.
---
 guile/starlet/clock.scm | 157 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 guile/starlet/clock.scm

diff --git a/guile/starlet/clock.scm b/guile/starlet/clock.scm
new file mode 100644
index 0000000..349aeb4
--- /dev/null
+++ b/guile/starlet/clock.scm
@@ -0,0 +1,157 @@
+;;
+;; starlet/clocks.scm
+;;
+;; Copyright © 2021 Thomas White <taw@bitwiz.org.uk>
+;;
+;; This file is part of Starlet.
+;;
+;; Starlet is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+;;
+;; This program 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 General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
+;;
+(define-module (starlet clock)
+  #:use-module (oop goops)
+  #:use-module (ice-9 exceptions)
+  #:export (<starlet-clock>
+            make-clock
+            stop-clock!
+            start-clock!
+            reverse-clock!
+
+            <starlet-delayed-clock>
+            make-delayed-clock
+
+            clock-stopped?
+            clock-reversed?
+            time-elapsed))
+
+
+(define (time-now)
+  (let ((a (gettimeofday)))
+    (+ (car a)
+       (/ (cdr a)
+          1000000))))
+
+
+;; "Real" clocks are straightforward objects for measuring differences in time
+;; between now and some point in the past, allowing for temporarily "pausing"
+;; the clock.  The time difference cannot be negative: if the start time is in
+;; the future, then "time-elapsed" will return 0.
+
+(define-class <starlet-clock> (<object>)
+  (start-real-time
+    #:init-form (time-now)
+    #:init-keyword #:start-time
+    #:getter get-start-real-time
+    #:setter set-start-real-time!)
+
+  (start-elapsed-time
+    #:init-value 0
+    #:getter get-start-elapsed-time
+    #:setter set-start-elapsed-time!)
+
+  (stopped
+    #:init-value #f
+    #:getter clock-stopped?
+    #:setter set-clock-stopped!)
+
+  (reversed
+    #:init-value #f
+    #:getter clock-reversed?
+    #:setter set-clock-reversed!))
+
+
+(define (make-clock)
+  (make <starlet-clock>))
+
+
+(define-method (time-elapsed (clock <starlet-clock>))
+  (if (clock-stopped? clock)
+      (get-start-elapsed-time clock)
+      (max 0
+           (if (clock-reversed? clock)
+
+               (- (get-start-elapsed-time clock)
+                  (- (time-now)
+                     (get-start-real-time clock)))
+
+               (+ (get-start-elapsed-time clock)
+                  (- (time-now)
+                     (get-start-real-time clock)))))))
+
+
+;; Stop the clock running
+(define-method (stop-clock! (clock <starlet-clock>))
+  (set-start-elapsed-time! clock (time-elapsed clock))
+  (set-clock-stopped! clock #t))
+
+
+;; Start the clock running (forwards)
+(define-method (start-clock! (clock <starlet-clock>))
+  (set-start-elapsed-time! clock (time-elapsed clock))
+  (set-start-real-time! clock (time-now))
+  (set-clock-reversed! clock #f)
+  (set-clock-stopped! clock #f))
+
+
+;; Start the clock running, backwards
+(define-method (reverse-clock! (clock <starlet-clock>))
+  (set-start-elapsed-time! clock (time-elapsed clock))
+  (set-start-real-time! clock (time-now))
+  (set-clock-reversed! clock #t)
+  (set-clock-stopped! clock #f))
+
+
+;; Delayed clocks refer to a parent clock for anything to do with "real" time.
+;; Note, however, that the parent clock can be another delayed clock.
+
+(define-class <starlet-delayed-clock> (<object>)
+  (parent
+    #:init-form (error "Parent clock must be specified")
+    #:init-keyword #:parent
+    #:getter get-parent-clock)
+
+  (delay-time
+    #:init-form (error "Delay time must be specified")
+    #:init-keyword #:delay-time
+    #:getter get-delay-time))
+
+
+(define-method (clock-stopped? (clock <starlet-delayed-clock>))
+  (clock-stopped? (get-parent-clock clock)))
+
+
+(define-method (clock-reversed? (clock <starlet-delayed-clock>))
+  (clock-reversed? (get-parent-clock clock)))
+
+
+(define-method (time-elapsed (clock <starlet-delayed-clock>))
+  (max 0 (- (time-elapsed (get-parent-clock clock))
+            (get-delay-time clock))))
+
+
+(define-method (stop-clock! (clock <starlet-delayed-clock>))
+  (error "Can only stop a top-level clock."))
+
+
+(define-method (start-clock! (clock <starlet-delayed-clock>))
+  (error "Can only start a top-level clock."))
+
+
+(define-method (reverse-clock! (clock <starlet-delayed-clock>))
+  (error "Can only reverse a top-level clock."))
+
+
+(define (make-delayed-clock clock delay-time)
+  (make <starlet-delayed-clock>
+        #:parent clock
+        #:delay-time delay-time))
-- 
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