diff --git a/src/window_func.h b/src/window_func.h
--- a/src/window_func.h
+++ b/src/window_func.h
@@ -56,4 +56,36 @@ void DeleteWindowByClass(WindowClass cls
 bool EditBoxInGlobalFocus();
 Point GetCaretPosition();
 
+/**
+ * Count how many times the interval has elapsed, and update the timer.
+ * Use to ensure a specific amount of events happen within a timeframe, e.g. for animation.
+ * The timer value does not need to be initialised.
+ * @param timer Timer to test. Value will be increased.
+ * @param delta Time since last test.
+ * @param interval Timing interval.
+ * @return Number of times the interval has elapsed.
+ */
+static inline uint CountIntervalElapsed(uint &timer, uint delta, uint interval)
+{
+	uint count = delta / interval;
+	if (timer + (delta % interval) >= interval) count++;
+	timer = (timer + delta) % interval;
+	return count;
+}
+
+/**
+ * Test if a timer has elapsed, and update the timer.
+ * Use to ensure an event happens only once within a timeframe, e.g. for window updates.
+ * The timer value must be initialised in order for the timer to elapsed.
+ * @param timer Timer to test. Value will be decreased.
+ * @param delta Time since last test.
+ * @return True iff the timer has elapsed.
+ */
+static inline bool TimerElapsed(int &timer, uint delta)
+{
+	if (timer <= 0) return false;
+	timer -= delta;
+	return timer <= 0;
+}
+
 #endif /* WINDOW_FUNC_H */