Added animation.

animation.go

@@ -0,0 +1,78 @@
+package zntg
+
+import "time"
+
+// Animation is a struct that keeps track of time for animation.
+type Animation struct {
+	// The interval of the animation
+	Interval time.Duration
+
+	active     bool
+	start      time.Time
+	lastUpdate time.Duration
+}
+
+// NewAnimation creates an Animation given the specified interval. The animation is immediately started.
+func NewAnimation(interval time.Duration) Animation {
+	return Animation{
+		Interval: interval,
+
+		active: true,
+		start:  time.Now(),
+	}
+}
+
+// NewAnimationPtr creates an Animation given the specified interval and returns a pointer to it. The animation is immediately started.
+func NewAnimationPtr(interval time.Duration) *Animation {
+	ani := NewAnimation(interval)
+	return &ani
+}
+
+// Animate checks if enough time as elapsed to animate a single interval and advances the single interval.
+func (a *Animation) Animate() bool {
+	since := time.Since(a.start)
+	if !a.active || since < a.lastUpdate+a.Interval {
+		return false
+	}
+	a.lastUpdate += a.Interval
+	return true
+}
+
+// AnimateDelta checks how many natural intervals have elapsed and advances that many intervals. Returns the total of time that has been advanced and the number of intervals.
+func (a *Animation) AnimateDelta() (time.Duration, int) {
+	if !a.active {
+		return 0, 0
+	}
+	since := time.Since(a.start)
+	n := (since - a.lastUpdate) / a.Interval
+	delta := n * a.Interval
+	a.lastUpdate += delta
+	return delta, int(n)
+}
+
+// AnimateFn calls fn for every interval and advances that interval for every interval that has elapsed until it caught up again.
+func (a *Animation) AnimateFn(fn func()) {
+	if !a.active {
+		return
+	}
+	since := time.Since(a.start)
+	for a.active && since > a.lastUpdate+a.Interval {
+		fn()
+		a.lastUpdate += a.Interval
+	}
+}
+
+// Pause pauses the animation causing the Animate{,Delta,Fn} methods to do nothing.
+func (a *Animation) Pause() {
+	a.active = false
+}
+
+// Start starts the animation (when paused or not started yet).
+func (a *Animation) Start() {
+	if a.active {
+		return
+	}
+	a.active = true
+	a.start = time.Now()
+	a.lastUpdate = 0
+}