Potential issue with Time.unscaledDeltaTime on 2018.2.20f1

Hi all,

I am encountering an issue with the Time.unscaledDeltaTime not being properly set when the application is paused or out of focus. I am running the following script on Android device using builds from 2017.2.0f3 and 2018.2.20f1. This is the scenario I am trying;

• Launch application
• Once loaded, I lock the device
  • I start a timer (on another device) to keep track of how long the game has been actually suspended
• I press the lock button on the device again and the application is resumed
  • Simultaneously I stop the timer
• The first Update call that gets executed should report that the Time.unscaledDeltaTime since last frame
  • The expected result is that the Time.unscaledDeltaTime is equal to the time that the application has been paused (roughly the same to that reported by the timer)
  • What I actually get is a value less than expected, say if the game has been suspended for 40s the Time.unscaledDeltaTime is set to 16s.
• This behaviour was noticed in 2018.2.20f1 but not reproducible on 2017.2.0f3 (works correctly here)

Can someone verify or explain why this is happening?

Code (CSharp):

1. using System;
2. using System.Text;
3. using UnityEngine;
4.  
5. public class TimeDemo : MonoBehaviour
6. {
7.     private bool logNextDeltaTime;
8.     private float lastUnscaledTime;
9.     private StringBuilder logBuilder;
10.  
11.     private void Awake()
12.     {
13.         logBuilder = new StringBuilder();
14.     }
15.  
16.     private void Update()
17.     {
18.         if (logNextDeltaTime)
19.         {
20.             var diff = Time.unscaledTime - lastUnscaledTime;
21.             logBuilder.AppendLine(string.Format("Application is updating frame {0} with time {1} (+{2}s). Time difference should be +{3}s", Time.frameCount, Time.unscaledTime, Time.unscaledDeltaTime, diff));
22.             logNextDeltaTime = false;
23.         }
24.     }
25.  
26.     private void OnApplicationFocus(bool focus)
27.     {
28.         logBuilder.AppendLine(string.Format("Application is focused - {0} in frame {1} with time {2}", focus, Time.frameCount, Time.unscaledTime));
29.         if (!focus)
30.         {
31.             logBuilder.AppendLine(string.Format("Last unscaled time {0}", Time.unscaledTime));
32.             lastUnscaledTime = Time.unscaledTime;
33.             logNextDeltaTime = true;
34.         }
35.     }
36.  
37.     private void OnApplicationPause(bool pause)
38.     {
39.         logBuilder.AppendLine(string.Format("Application is paused - {0} in frame {1} with time {2}", pause, Time.frameCount, Time.unscaledTime));
40.         if (pause)
41.         {
42.             logBuilder.AppendLine(string.Format("Last unscaled time {0}", Time.unscaledTime));
43.             lastUnscaledTime = Time.unscaledTime;
44.             logNextDeltaTime = true;
45.         }
46.     }
47.  
48.     private void OnGUI()
49.     {
50.         GUI.skin.GetStyle("label").fontSize = 35;
51.         GUI.skin.GetStyle("button").fontSize = 35;
52.  
53.         if(GUILayout.Button("Clear Log", GUILayout.Width(300), GUILayout.Height(100)))
54.         {
55.             logBuilder = new StringBuilder();
56.         }
57.  
58.         GUILayout.Label(logBuilder.ToString());
59.     }
60. }

 

A weird fact that I noticed is that when the Android device is connected via USB with the machine, the unscaledDeltaTime values are correct. When it is disconnected, it doesn't work as expected. I updated the code to use the Android elapsedTime from its local clock and the values received are correct as seen in Unity 2017.2.0f3.

Can someone confirm this issue?

Code (CSharp):

1. using System;
2. using System.Text;
3. using UnityEngine;
4.  
5. public class TimeDemo : MonoBehaviour
6. {
7.     private bool logNextDeltaTime;
8.     private float prevTimestamp;
9.     private StringBuilder logBuilder;
10.  
11.     private void Awake()
12.     {
13.         logBuilder = new StringBuilder();
14.     }
15.  
16.     private void Update()
17.     {
18.         if (logNextDeltaTime)
19.         {
20.             #if UNITY_ANDROID && !UNITY_EDITOR
21.             var currTimestamp = UnscaledTime();
22.             #else
23.             var currTimestamp = Time.unscaledTime;
24.             #endif
25.  
26.             var diff = currTimestamp - prevTimestamp;
27.             logBuilder.AppendLine(string.Format("Application is updating frame {0} with time {1} (+{2}s). Time difference should be +{3}s", Time.frameCount, Time.unscaledTime, Time.unscaledDeltaTime, diff));
28.             logNextDeltaTime = false;
29.         }
30.     }
31.  
32.     private void OnApplicationFocus(bool focus)
33.     {
34.         logBuilder.AppendLine(string.Format("Application is focused - {0} in frame {1} with time {2}", focus, Time.frameCount, Time.unscaledTime));
35.         if (!focus)
36.         {
37.             OnSuspended();
38.         }
39.     }
40.  
41.     private void OnApplicationPause(bool pause)
42.     {
43.         logBuilder.AppendLine(string.Format("Application is paused - {0} in frame {1} with time {2}", pause, Time.frameCount, Time.unscaledTime));
44.         if (pause)
45.         {
46.             OnSuspended();
47.         }
48.     }
49.  
50.     private void OnGUI()
51.     {
52.         GUI.skin.GetStyle("label").fontSize = 35;
53.         GUI.skin.GetStyle("button").fontSize = 35;
54.  
55.         if(GUILayout.Button("Clear Log", GUILayout.Width(300), GUILayout.Height(100)))
56.         {
57.             logBuilder = new StringBuilder();
58.         }
59.  
60.         GUILayout.Label(logBuilder.ToString());
61.     }
62.  
63.     private void OnSuspended()
64.     {
65.         #if UNITY_ANDROID && !UNITY_EDITOR
66.         prevTimestamp = UnscaledTime();
67.         #else
68.         prevTimestamp = Time.unscaledTime;
69.         #endif
70.  
71.         logNextDeltaTime = true;
72.         logBuilder.AppendLine(string.Format("Last unscaled time {0}", prevTimestamp));
73.     }
74.  
75.     private float UnscaledTime()
76.     {
77.         var systemClock = new AndroidJavaClass("android.os.SystemClock");
78.         return systemClock.CallStatic<long>("elapsedRealtime") / 1000f;
79.     }
80. }