Add delta time to stats

pkg/timing/frameStats.go

@@ -8,15 +8,18 @@ import (
 )
 
 type FrameStats struct {
-	Fps    *Fps
-	frames map[uint32]time.Time
-	mutex  sync.Mutex
+	Fps        *Fps
+	frames     map[uint32]time.Time
+	mutex      sync.Mutex
+	lastTime   *time.Time
+	deltaTimes map[uint32]time.Duration
 }
 
 func NewFrameStats(timeWindow time.Duration) (s *FrameStats) {
 	s = new(FrameStats)
 	s.Fps = NewFps(timeWindow)
 	s.frames = map[uint32]time.Time{}
+	s.deltaTimes = map[uint32]time.Duration{}
 	return s
 }
 
@@ -25,6 +28,10 @@ func (s *FrameStats) Add(frameId uint32, t time.Time) {
 	defer s.mutex.Unlock()
 	s.frames[frameId] = t
 	s.Fps.Inc()
+	if s.lastTime != nil {
+		s.deltaTimes[frameId] = t.Sub(*s.lastTime)
+	}
+	s.lastTime = &t
 }
 
 func (s *FrameStats) Prune(to time.Time) {
@@ -33,6 +40,7 @@ func (s *FrameStats) Prune(to time.Time) {
 	for frameId, t := range s.frames {
 		if t.Before(to) {
 			delete(s.frames, frameId)
+			delete(s.deltaTimes, frameId)
 		}
 	}
 }
@@ -41,6 +49,7 @@ func (s *FrameStats) Clear() {
 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 	s.frames = map[uint32]time.Time{}
+	s.deltaTimes = map[uint32]time.Duration{}
 	s.Fps.Clear()
 }
 
@@ -61,12 +70,31 @@ func (s *FrameStats) Quality() float64 {
 	return sum / float64(max-min+1)
 }
 
+func (s *FrameStats) DeltaTime() (mu float64, stdDev float64) {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+	var sum time.Duration
+	for _, dt := range s.deltaTimes {
+		sum += dt
+	}
+	mu = sum.Seconds() / float64(len(s.deltaTimes))
+
+	var sqSum float64
+	for _, dt := range s.deltaTimes {
+		diff := mu - dt.Seconds()
+		sqSum += diff * diff
+	}
+	stdDev = math.Sqrt(sqSum / float64(len(s.deltaTimes)))
+	return
+}
+
 func (s *FrameStats) NumFrames() int {
 	return len(s.frames)
 }
 
 func (s *FrameStats) String() string {
 	fps := s.Fps.Float32()
 	quality := s.Quality()
-	return fmt.Sprintf("%v @ %3.0f fps", colorizePercent(quality), fps)
+	dt, dtStdDev := s.DeltaTime()
+	return fmt.Sprintf("%v @ %3.0f fps | Δ %.1fms σ %.3f", colorizePercent(quality), fps, dt*1000, dtStdDev*1000)
 }