Make the ios FPSCounterView more stable

* Calculate the accumulated frame rate over the entire update interval.

* Update FPS when we actually draw, instead of when we advance the animation.

Diffs=
1ec31ffba Make the ios FPSCounterView more stable

.rive_head

@@ -1 +1 @@
-331ad0d55068e5059f3e9c85af5382836e278e4e
+1ec31ffba21a7e07c72c6062d0a522a383ffc7e4

Source/RiveView.swift

@@ -142,7 +142,6 @@ open class RiveView: RiveRendererView {
 
         // Calculate the time elapsed between ticks
         let elapsedTime = timestamp - lastTime
-        fpsCounter?.elapsed(time: elapsedTime)
         lastTime = timestamp
         advance(delta: elapsedTime)
         if !isPlaying {
@@ -195,6 +194,10 @@ open class RiveView: RiveRendererView {
         let newFrame = CGRect(origin: rect.origin, size: size)
         align(with: newFrame, contentRect: riveModel.artboard.bounds(), alignment: alignment, fit: fit)
         draw(with: riveModel.artboard)
+
+        if let displayLink = displayLinkProxy?.displayLink {
+            fpsCounter?.didDrawFrame(timestamp:displayLink.timestamp)
+        }
     }
 
     // MARK: - UIResponder

Source/Utils/FPSCounterView.swift

@@ -10,8 +10,9 @@ import UIKit
 
 class FPSCounterView: UILabel {
     private let fpsFormatter = NumberFormatter()
-    private let updateInterval: Double = 0.5
-    private var timeSinceUpdate: Double = 0
+    private let updateInterval: Double = 1.0
+    private var timestampOnLastUpdate: CFTimeInterval = 0
+    private var framesDrawnSinceLastUpdate: Int = 0
 
     internal convenience init() {
         self.init(frame: CGRect(x: 1, y: 1, width: 70, height: 20))
@@ -29,14 +30,20 @@ class FPSCounterView: UILabel {
         fpsFormatter.roundingMode = .down
     }
 
-    internal func elapsed(time elapsedTime: Double) {
-        if elapsedTime != 0 {
-            timeSinceUpdate += elapsedTime
-
-            if timeSinceUpdate >= updateInterval {
-                timeSinceUpdate = 0
-                text = fpsFormatter.string(from: NSNumber(value: 1 / elapsedTime))! + "fps"
-            }
+    internal func didDrawFrame(timestamp: CFTimeInterval) {
+        if (timestampOnLastUpdate == 0) {
+            timestampOnLastUpdate = timestamp
+            framesDrawnSinceLastUpdate = 0
+            return
+        }
+
+        framesDrawnSinceLastUpdate += 1
+
+        let elapsedSinceLastUpdate = timestamp - timestampOnLastUpdate
+        if elapsedSinceLastUpdate >= updateInterval {
+            text = fpsFormatter.string(from: NSNumber(value: Double(framesDrawnSinceLastUpdate) / elapsedSinceLastUpdate))! + "fps"
+            timestampOnLastUpdate = timestamp
+            framesDrawnSinceLastUpdate = 0
         }
     }