From aea9775e4dba802a6ac766b9757020ea43a5f94e Mon Sep 17 00:00:00 2001
From: Stephen Birarda <commit@birarda.com>
Date: Wed, 5 Sep 2018 16:55:46 -0700
Subject: [PATCH] get back to ideal frame time when slow

---
 assignment-client/src/audio/AudioMixer.cpp | 29 +++++++++++-----------
 assignment-client/src/audio/AudioMixer.h   |  5 +++-
 2 files changed, 18 insertions(+), 16 deletions(-)

diff --git a/assignment-client/src/audio/AudioMixer.cpp b/assignment-client/src/audio/AudioMixer.cpp
index bba3398cbd..b5318a72d9 100644
--- a/assignment-client/src/audio/AudioMixer.cpp
+++ b/assignment-client/src/audio/AudioMixer.cpp
@@ -386,15 +386,18 @@ void AudioMixer::start() {
 
     // mix state
     unsigned int frame = 1;
-    auto frameTimestamp = p_high_resolution_clock::now();
 
     while (!_isFinished) {
         auto ticTimer = _ticTiming.timer();
 
-        {
-            auto timer = _checkTimeTiming.timer();
-            auto frameDuration = timeFrame(frameTimestamp);
-            throttle(frameDuration, frame);
+        if (_startFrameTimestamp.time_since_epoch().count() == 0) {
+            _startFrameTimestamp = _idealFrameTimestamp = p_high_resolution_clock::now();
+        } else {
+            {
+                auto timer = _checkTimeTiming.timer();
+                auto frameDuration = timeFrame();
+                throttle(frameDuration, frame);
+            }
         }
 
         auto frameTimer = _frameTiming.timer();
@@ -449,26 +452,22 @@ void AudioMixer::start() {
     }
 }
 
-chrono::microseconds AudioMixer::timeFrame(p_high_resolution_clock::time_point& timestamp) {
+chrono::microseconds AudioMixer::timeFrame() {
     // advance the next frame
-    auto nextTimestamp = timestamp + chrono::microseconds(AudioConstants::NETWORK_FRAME_USECS);
     auto now = p_high_resolution_clock::now();
 
     // compute how long the last frame took
-    auto duration = chrono::duration_cast<chrono::microseconds>(now - timestamp);
+    auto duration = chrono::duration_cast<chrono::microseconds>(now - _startFrameTimestamp);
 
-    // set the new frame timestamp
-    timestamp = max(now, nextTimestamp);
+    _idealFrameTimestamp += chrono::microseconds(AudioConstants::NETWORK_FRAME_USECS);
 
     {
         auto timer = _sleepTiming.timer();
-
-        // sleep until the next frame should start
-        // WIN32 sleep_until is broken until VS2015 Update 2
-        // instead, max (above) guarantees that timestamp >= now, so we can sleep_for
-        this_thread::sleep_for(timestamp - now);
+        this_thread::sleep_until(_idealFrameTimestamp);
     }
 
+    _startFrameTimestamp = p_high_resolution_clock::now();
+
     return duration;
 }
 
diff --git a/assignment-client/src/audio/AudioMixer.h b/assignment-client/src/audio/AudioMixer.h
index 99b01683bf..b8ea0d5c58 100644
--- a/assignment-client/src/audio/AudioMixer.h
+++ b/assignment-client/src/audio/AudioMixer.h
@@ -84,7 +84,7 @@ private slots:
 
 private:
     // mixing helpers
-    std::chrono::microseconds timeFrame(p_high_resolution_clock::time_point& timestamp);
+    std::chrono::microseconds timeFrame();
     void throttle(std::chrono::microseconds frameDuration, int frame);
 
     AudioMixerClientData* getOrCreateClientData(Node* node);
@@ -94,6 +94,9 @@ private:
     void parseSettingsObject(const QJsonObject& settingsObject);
     void clearDomainSettings();
 
+    p_high_resolution_clock::time_point _idealFrameTimestamp;
+    p_high_resolution_clock::time_point _startFrameTimestamp;
+
     float _trailingMixRatio { 0.0f };
     float _throttlingRatio { 0.0f };