[beast/ebeast] EBEAST: widgets.js: provide helpers for AnimationFrame callbacks

[Tim Janik <timj src gnome org>]

commit bf05c70e7e3973c37644096266d6392221e3b5fd
Author: Tim Janik <timj gnu org>
Date:   Tue Mar 7 00:42:53 2017 +0100

    EBEAST: widgets.js: provide helpers for AnimationFrame callbacks
    
    Signed-off-by: Tim Janik <timj gnu org>

 ebeast/assets/widgets.js |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)
---
diff --git a/ebeast/assets/widgets.js b/ebeast/assets/widgets.js
index fe94e1a..249a35d 100644
--- a/ebeast/assets/widgets.js
+++ b/ebeast/assets/widgets.js
@@ -10,3 +10,25 @@ module.exports.KeyCode = {
   VOLUMEMUTE: 173, VOLUMEDOWN: 174, VOLUMEUP: 175, MEDIANEXTTRACK: 176, MEDIAPREVIOUSTRACK: 177, MEDIASTOP: 
178, MEDIAPLAYPAUSE: 179,
 };
 
+// == Utility Functions ==
+
+/// Wrap @a callback so it's only called once per AnimationFrame.
+function create_animation_callback (callback) {
+  return function() {
+    if (true === !callback.__create_animation_callback__pending__) {
+      const request_id = requestAnimationFrame (function (now_ms) {
+       callback.__create_animation_callback__pending__ = undefined;
+       callback (now_ms);
+      });
+      callback.__create_animation_callback__pending__ = request_id;
+    }
+  };
+}
+module.exports.create_animation_callback = create_animation_callback;
+
+/// Enqueue @a callback to be executed once at the next AnimationFrame.
+function queue_animation_callback (callback) {
+  const queue_callback = create_animation_callback (callback);
+  queue_callback();
+}
+module.exports.queue_animation_callback = queue_animation_callback;