From 507bb03bea5c141cf1d52566f4fa89f149339af6 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Sun, 23 May 2021 13:44:10 -0400
Subject: [PATCH 01/22] Fix half-double initialization issues

---
 src/engine/enginebuffer.cpp       |  1 +
 src/engine/enginemaster.cpp       |  5 ++
 src/engine/sync/enginesync.cpp    | 96 +++++++++++++++++++++++++------
 src/engine/sync/enginesync.h      |  4 +-
 src/engine/sync/internalclock.cpp |  3 +
 src/engine/sync/internalclock.h   |  1 +
 src/engine/sync/syncable.h        |  5 ++
 src/engine/sync/synccontrol.cpp   | 50 ++++++++++++----
 src/engine/sync/synccontrol.h     |  3 +-
 src/test/enginesynctest.cpp       | 15 +++--
 10 files changed, 147 insertions(+), 36 deletions(-)

diff --git a/src/engine/enginebuffer.cpp b/src/engine/enginebuffer.cpp
index 80065ba2b25..4a5d011d40b 100644
--- a/src/engine/enginebuffer.cpp
+++ b/src/engine/enginebuffer.cpp
@@ -1297,6 +1297,7 @@ void EngineBuffer::postProcess(const int iBufferSize) {
     }
     double localBpm = m_pBpmControl->updateLocalBpm();
     double beatDistance = m_pBpmControl->updateBeatDistance();
+    qDebug() << getGroup() << "beat distance updated" << beatDistance;
     m_pSyncControl->setLocalBpm(localBpm);
     m_pSyncControl->updateAudible();
     SyncMode mode = m_pSyncControl->getSyncMode();
diff --git a/src/engine/enginemaster.cpp b/src/engine/enginemaster.cpp
index 33cd29d5e42..cda9a1dbb51 100644
--- a/src/engine/enginemaster.cpp
+++ b/src/engine/enginemaster.cpp
@@ -369,6 +369,11 @@ void EngineMaster::processChannels(int iBufferSize) {
 
     // Do internal master sync post-processing before the other
     // channels.
+    // OK, so this means the internal clock knows that it has crossed a beat
+    // boundary before the channels do. This means when we call this, we
+    // notify all the channels that the master beat distance has changed.
+    // They try to update the target beat distance, and guess the
+    // wrong number because they can't do half/double calculation correctly.
     m_pMasterSync->onCallbackEnd(m_iSampleRate, m_iBufferSize);
 
     // After all the engines have been processed, trigger post-processing
diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 7602283d22d..f913eb8c73d 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -96,8 +96,15 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    if (noPlayingFollowers() && m_pMasterSyncable) {
-        m_pMasterSyncable->notifyOnlyPlayingSyncable();
+    auto players = getPlayingSyncables();
+    if (players.size() == 1) {
+        qDebug() << "!!!!!!!!!!!!!!!!!!!!!1there is only one playing syncable, tell it so!";
+        players.at(0)->notifyOnlyPlayingSyncable();
+    } else {
+        qDebug() << "players!";
+        for (auto* play : players) {
+            qDebug() << play->getGroup();
+        }
     }
 }
 
@@ -350,11 +357,31 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
 
     if (newMaster != nullptr && newMaster != m_pMasterSyncable) {
         activateMaster(newMaster, SYNC_MASTER_SOFT);
-    }
-
-    if (noPlayingFollowers() && m_pMasterSyncable) {
-        m_pMasterSyncable->notifyOnlyPlayingSyncable();
-        setMasterParams(m_pMasterSyncable);
+        setMasterParams(newMaster);
+    }
+
+    // we know for a fact that pSyncable is playing and audible.
+    // We want to init master params
+    // cases:
+    // just we are playing: set master params with our settings
+    // NO. just because we are master, doesn't mean we win! we might be copying someone else.
+    // if anything we should JUST init beat distance.
+    // another deck is playing and it's master: don't touch it
+    // another deck is playing and it's not master: don't touch it
+    auto players = getPlayingSyncables();
+    if (players.size() == 1) {
+        Syncable* onlyPlayer = players.at(0);
+        qDebug() << "2222222222222222222222222222 there is only one playing "
+                    "syncable, it gets to set beat dist"
+                 << onlyPlayer->getGroup();
+        onlyPlayer->notifyOnlyPlayingSyncable();
+        // setMasterParams(onlyPlayer);
+        setMasterBeatDistance(onlyPlayer, onlyPlayer->getBeatDistance());
+    } else {
+        qDebug() << "players!";
+        for (auto* play : players) {
+            qDebug() << play->getGroup();
+        }
     }
 
     pSyncable->requestSync();
@@ -597,35 +624,72 @@ void EngineSync::setMasterBeatDistance(Syncable* pSource, double beatDistance) {
 }
 
 void EngineSync::setMasterParams(Syncable* pSource) {
-    const double beatDistance = pSource->getBeatDistance();
+    // so the bug here is that we are setting the master parameters from some source, but
+    // that source may not be the master! but when we update the multipliers, we update
+    // based on who is master. We used to try to force master to be multiplier 1.0, but that
+    // causes problems.
+
+    pSource->notifyMasterParamSource();
+
+    double beatDistance = pSource->getBeatDistance();
+    // // If the params source is not playing, but other syncables are, then we are a stopped
+    // // explicit Master and we should not initialize the beat distance.  Take it from the
+    // // internal clock instead.
+    if (!pSource->isPlaying()) {
+        bool playingSyncables = false;
+        for (Syncable* pSyncable : m_syncables) {
+            qDebug() << "checking" << pSyncable->getGroup();
+            if (pSyncable == pSource) {
+                continue;
+            }
+            if (!pSyncable->isSynchronized()) {
+                continue;
+            }
+            qDebug() << "it's valid";
+            if (pSyncable->isPlaying()) {
+                qDebug() << "found a playing syncable" << pSyncable->getGroup();
+                playingSyncables = true;
+                break;
+            }
+        }
+        if (playingSyncables) {
+            qDebug() << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
+                        "BaseSyncableListener::setMasterParams, not playing, "
+                        "playing followers, pull from internal clock"
+                     << pSource->getGroup();
+            beatDistance = m_pInternalClock->getBeatDistance();
+        }
+    }
+    // Do we want the RAW values here, not multiplied by adjust factor??
     const double baseBpm = pSource->getBaseBpm();
     double bpm = pSource->getBpm();
     if (bpm <= 0) {
         bpm = baseBpm;
     }
-    // qDebug() << "BaseSyncableListener::setMasterParams, source is"
-    //          << pSource->getGroup() << beatDistance << baseBpm << bpm;
+    qDebug() << "BaseSyncableListener::setMasterParams, source is"
+             << pSource->getGroup() << beatDistance << baseBpm << bpm;
     if (pSource != m_pInternalClock) {
         m_pInternalClock->setMasterParams(beatDistance, baseBpm, bpm);
     }
     foreach (Syncable* pSyncable, m_syncables) {
-        if (pSyncable == pSource || !pSyncable->isSynchronized()) {
+        // not sure if we should skip the pSource here.
+        if (!pSyncable->isSynchronized()) {
             continue;
         }
         pSyncable->setMasterParams(beatDistance, baseBpm, bpm);
     }
 }
 
-bool EngineSync::noPlayingFollowers() const {
+QList<Syncable*> EngineSync::getPlayingSyncables() const {
+    QList<Syncable*> players;
     for (Syncable* pSyncable : m_syncables) {
         if (!pSyncable->isSynchronized()) {
             continue;
         }
 
-        if (pSyncable->isPlaying() && pSyncable->isAudible() &&
-                isFollower(pSyncable->getSyncMode())) {
-            return false;
+        if (pSyncable->isPlaying()) {
+            players.append(pSyncable);
         }
     }
-    return true;
+    return players;
 }
diff --git a/src/engine/sync/enginesync.h b/src/engine/sync/enginesync.h
index 426c5256f88..8e306e14a91 100644
--- a/src/engine/sync/enginesync.h
+++ b/src/engine/sync/enginesync.h
@@ -115,8 +115,8 @@ class EngineSync : public SyncableListener {
 
     void setMasterParams(Syncable* pSource);
 
-    /// Check if there are no playing followers left.
-    bool noPlayingFollowers() const;
+    /// Return the playing syncables, if any. This is used to initialize beat distance settings.
+    QList<Syncable*> getPlayingSyncables() const;
 
     /// Only for testing. Do not use.
     Syncable* getSyncableForGroup(const QString& group);
diff --git a/src/engine/sync/internalclock.cpp b/src/engine/sync/internalclock.cpp
index 8ecfe8b27ad..8c3731f2397 100644
--- a/src/engine/sync/internalclock.cpp
+++ b/src/engine/sync/internalclock.cpp
@@ -140,6 +140,9 @@ void InternalClock::setInstantaneousBpm(double bpm) {
     Q_UNUSED(bpm);
 }
 
+void InternalClock::notifyMasterParamSource() {
+}
+
 void InternalClock::setMasterParams(double beatDistance, double baseBpm, double bpm) {
     if (kLogger.traceEnabled()) {
         kLogger.trace() << "InternalClock::setMasterParams" << beatDistance << baseBpm << bpm;
diff --git a/src/engine/sync/internalclock.h b/src/engine/sync/internalclock.h
index 88ecfb38c6f..dea03a490d7 100644
--- a/src/engine/sync/internalclock.h
+++ b/src/engine/sync/internalclock.h
@@ -52,6 +52,7 @@ class InternalClock : public QObject, public Clock, public Syncable {
 
     double getBaseBpm() const override;
     void setMasterBpm(double bpm) override;
+    void notifyMasterParamSource() override;
     double getBpm() const override;
     void setInstantaneousBpm(double bpm) override;
     void setMasterParams(double beatDistance, double baseBpm, double bpm) override;
diff --git a/src/engine/sync/syncable.h b/src/engine/sync/syncable.h
index d25e54d0a09..19678be6229 100644
--- a/src/engine/sync/syncable.h
+++ b/src/engine/sync/syncable.h
@@ -112,6 +112,11 @@ class Syncable {
     // signal loops could occur.
     virtual void setMasterBpm(double bpm) = 0;
 
+    // Tells a Syncable that it's going to be used as a source for master
+    // params. This is a gross hack so that the SyncControl can undo its
+    // half/double adjustment.
+    virtual void notifyMasterParamSource() = 0;
+
     // Combines the above three calls into one, since they are often set
     // simultaneously.  Avoids redundant recalculation that would occur by
     // using the three calls separately.
diff --git a/src/engine/sync/synccontrol.cpp b/src/engine/sync/synccontrol.cpp
index 060cab53257..9c9a3c0b9d0 100644
--- a/src/engine/sync/synccontrol.cpp
+++ b/src/engine/sync/synccontrol.cpp
@@ -212,6 +212,7 @@ void SyncControl::setMasterBeatDistance(double beatDistance) {
     // Set the BpmControl target beat distance to beatDistance, adjusted by
     // the multiplier if in effect.  This way all of the multiplier logic
     // is contained in this single class.
+    m_lastTargetBeatDistance = m_unmultipliedTargetBeatDistance;
     m_unmultipliedTargetBeatDistance = beatDistance;
     // Update the target beat distance based on the multiplier.
     updateTargetBeatDistance();
@@ -238,19 +239,37 @@ void SyncControl::setMasterBpm(double bpm) {
     }
 }
 
+void SyncControl::notifyMasterParamSource() {
+    m_masterBpmAdjustFactor = kBpmUnity;
+}
+
 void SyncControl::setMasterParams(
         double beatDistance, double baseBpm, double bpm) {
+    qDebug() << "SyncControl::setMasterParams" << getGroup() << beatDistance << baseBpm << bpm;
+    // if (paramSource == this) {
+    //     baseBpm *= m_masterBpmAdjustFactor;
+    //     bpm *= m_masterBpmAdjustFactor;
+    //     qDebug() << "we were param source, undo adjust factor:" << baseBpm << bpm;
+    // }
     // Calculate the factor for the file bpm. That gives the best
     // result at any rate slider position.
-    double masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    if (isMaster(getSyncMode())) {
-        // In Master mode we adjust the incoming Bpm for the initial sync.
-        bpm *= masterBpmAdjustFactor;
-        m_masterBpmAdjustFactor = kBpmUnity;
-    } else {
-        // in Follower mode we keep the factor when reporting our BPM
-        m_masterBpmAdjustFactor = masterBpmAdjustFactor;
-    }
+    qDebug() << "file bpm: " << fileBpm();
+
+    // masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    // double masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    // if (paramSource == this) {
+    //     //     qDebug() << "We were param source!";
+    //     //     // If we are the param source, we need to undo the adjustment factor
+    //     //     // or else we start piling multipliers on top of each other.
+    //     //     bpm *= masterBpmAdjustFactor;
+    //     m_masterBpmAdjustFactor = kBpmUnity;
+    // } else {
+    //     m_masterBpmAdjustFactor = masterBpmAdjustFactor;
+    // }
+
+    // m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    qDebug() << "ADJUST FACTOR?!" << m_masterBpmAdjustFactor;
     setMasterBpm(bpm);
     setMasterBeatDistance(beatDistance);
 }
@@ -274,7 +293,10 @@ double SyncControl::determineBpmMultiplier(double myBpm, double targetBpm) const
 void SyncControl::updateTargetBeatDistance() {
     double targetDistance = m_unmultipliedTargetBeatDistance;
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "SyncControl::updateTargetBeatDistance, unmult distance" << targetDistance;
+        kLogger.trace()
+                << getGroup()
+                << "SyncControl::updateTargetBeatDistance, unmult distance"
+                << targetDistance << m_masterBpmAdjustFactor;
     }
 
     // Determining the target distance is not as simple as x2 or /2.  Since one
@@ -289,7 +311,9 @@ void SyncControl::updateTargetBeatDistance() {
         targetDistance *= kBpmDouble;
     } else if (m_masterBpmAdjustFactor == kBpmHalve) {
         targetDistance *= kBpmHalve;
-        if (m_pBeatDistance->get() >= 0.5) {
+        qDebug() << "my beat dist" << m_pBeatDistance->get();
+        // Our beat distance CO is still a buffer behind, so take the current value.
+        if (m_pBpmControl->getBeatDistance(getSampleOfTrack().current) >= 0.5) {
             targetDistance += 0.5;
         }
     }
@@ -301,7 +325,8 @@ void SyncControl::updateTargetBeatDistance() {
 
 double SyncControl::getBpm() const {
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "SyncControl::getBpm()";
+        kLogger.trace() << getGroup() << "SyncControl::getBpm()"
+                        << m_pBpm->get() << "/" << m_masterBpmAdjustFactor;
     }
     return m_pBpm->get() / m_masterBpmAdjustFactor;
 }
@@ -441,6 +466,7 @@ void SyncControl::setLocalBpm(double local_bpm) {
     if (local_bpm == m_prevLocalBpm.getValue()) {
         return;
     }
+    qDebug() << "SyncControl::setLocalBpm" << getGroup() << local_bpm;
     m_prevLocalBpm.setValue(local_bpm);
 
     SyncMode syncMode = getSyncMode();
diff --git a/src/engine/sync/synccontrol.h b/src/engine/sync/synccontrol.h
index ccdff1e4f54..32781b42ff3 100644
--- a/src/engine/sync/synccontrol.h
+++ b/src/engine/sync/synccontrol.h
@@ -48,10 +48,10 @@ class SyncControl : public EngineControl, public Syncable {
     // Must never result in a call to
     // SyncableListener::notifyBeatDistanceChanged or signal loops could occur.
     void setMasterBeatDistance(double beatDistance) override;
-
     // Must never result in a call to
     // SyncableListener::notifyBpmChanged or signal loops could occur.
     void setMasterBpm(double bpm) override;
+    void notifyMasterParamSource() override;
     void setMasterParams(double beatDistance, double baseBpm, double bpm) override;
 
     // Must never result in a call to
@@ -113,6 +113,7 @@ class SyncControl : public EngineControl, public Syncable {
     // It is handy to store the raw reported target beat distance in case the
     // multiplier changes and we need to recalculate the target distance.
     double m_unmultipliedTargetBeatDistance;
+    double m_lastTargetBeatDistance;
     ControlValueAtomic<double> m_prevLocalBpm;
     QAtomicInt m_audible;
 
diff --git a/src/test/enginesynctest.cpp b/src/test/enginesynctest.cpp
index 7d00c4a7e2e..39a216db188 100644
--- a/src/test/enginesynctest.cpp
+++ b/src/test/enginesynctest.cpp
@@ -1660,14 +1660,16 @@ TEST_F(EngineSyncTest, HalfDoubleBpmTest) {
             ->set(SYNC_FOLLOWER);
 
     // Mixxx will choose the first playing deck to be master.  Let's start deck 2 first.
+    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch2 play";
     ControlObject::getControl(ConfigKey(m_sGroup2, "play"))->set(1.0);
+    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch1 play";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
     ProcessBuffer();
 
-    EXPECT_EQ(1.0,
+    EXPECT_EQ(0.5,
             m_pChannel1->getEngineBuffer()
                     ->m_pSyncControl->m_masterBpmAdjustFactor);
-    EXPECT_EQ(2.0,
+    EXPECT_EQ(1.0,
             m_pChannel2->getEngineBuffer()
                     ->m_pSyncControl->m_masterBpmAdjustFactor);
     EXPECT_DOUBLE_EQ(
@@ -1789,7 +1791,7 @@ TEST_F(EngineSyncTest, HalfDoubleThenPlay) {
 
     ProcessBuffer();
 
-    EXPECT_DOUBLE_EQ(87.5,
+    EXPECT_DOUBLE_EQ(175,
             ControlObject::getControl(ConfigKey(m_sInternalClockGroup, "bpm"))
                     ->get());
 
@@ -1997,7 +1999,9 @@ TEST_F(EngineSyncTest, SyncPhaseToPlayingNonSyncDeck) {
     // Next Deck becomes master and the Master clock is set to 100 BPM
     // The 130 BPM Track should be played at 100 BPM, rate = 0.769230769
     pButtonSyncEnabled1->set(1.0);
+    qDebug() << "PUSH PLAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAY";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
+
     // Beat length: 40707.692307692305
     // Buffer size is 1024 at 44.1 kHz at the given rate = 787.692307692 Samples
     // Expected beat_distance = 0.019349962
@@ -2021,12 +2025,13 @@ TEST_F(EngineSyncTest, SyncPhaseToPlayingNonSyncDeck) {
 
     ProcessBuffer();
 
-    // we expect that Deck 1 distance has not changed and the internal clock follows it exactly.
+    // we expect that Deck 1 distance has not changed but the internal clock keeps going, because
+    // the internal clock should continue playing even if the leader is stopped.
     EXPECT_TRUE(isSoftMaster(m_sGroup1));
     EXPECT_NEAR(0.019349962,
             ControlObject::getControl(ConfigKey(m_sGroup1, "beat_distance"))->get(),
             kMaxFloatingPointErrorLowPrecision);
-    EXPECT_NEAR(0.019349962,
+    EXPECT_NEAR(0.038699924,
             ControlObject::getControl(ConfigKey(m_sInternalClockGroup, "beat_distance"))->get(),
             kMaxFloatingPointErrorLowPrecision);
 

From 0718058bfc098070bd6323d0e64d9d9a505b7418 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Sun, 23 May 2021 14:29:36 -0400
Subject: [PATCH 02/22] Sync Lock: Fix more half/double issues and clean up for
 PR

---
 src/engine/controls/bpmcontrol.cpp |  6 ++-
 src/engine/enginebuffer.cpp        |  1 -
 src/engine/enginemaster.cpp        |  8 ++-
 src/engine/sync/enginesync.cpp     | 83 +++++++++++-------------------
 src/engine/sync/enginesync.h       |  5 +-
 src/engine/sync/syncable.h         |  2 +-
 src/engine/sync/synccontrol.cpp    | 31 ++---------
 src/engine/sync/synccontrol.h      |  1 -
 src/test/enginesynctest.cpp        | 21 ++++++--
 9 files changed, 61 insertions(+), 97 deletions(-)

diff --git a/src/engine/controls/bpmcontrol.cpp b/src/engine/controls/bpmcontrol.cpp
index 3dae2ae609a..fac2e68e87d 100644
--- a/src/engine/controls/bpmcontrol.cpp
+++ b/src/engine/controls/bpmcontrol.cpp
@@ -536,7 +536,9 @@ double BpmControl::getBeatDistance(double dThisPosition) const {
     // we don't adjust the reported distance the track will try to adjust
     // sync against itself.
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "BpmControl::getBeatDistance" << dThisPosition;
+        kLogger.trace() << getGroup()
+                        << "BpmControl::getBeatDistance. dThisPosition:"
+                        << dThisPosition;
     }
     double dPrevBeat = m_pPrevBeat->get();
     double dNextBeat = m_pNextBeat->get();
@@ -560,7 +562,7 @@ double BpmControl::getBeatDistance(double dThisPosition) const {
     }
 
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "BpmControl::getBeatDistance"
+        kLogger.trace() << getGroup() << "BpmControl::getBeatDistance. dBeatPercentage:"
                         << dBeatPercentage << "-  offset "
                         << m_dUserOffset.getValue() << " =  "
                         << (dBeatPercentage - m_dUserOffset.getValue());
diff --git a/src/engine/enginebuffer.cpp b/src/engine/enginebuffer.cpp
index 4a5d011d40b..80065ba2b25 100644
--- a/src/engine/enginebuffer.cpp
+++ b/src/engine/enginebuffer.cpp
@@ -1297,7 +1297,6 @@ void EngineBuffer::postProcess(const int iBufferSize) {
     }
     double localBpm = m_pBpmControl->updateLocalBpm();
     double beatDistance = m_pBpmControl->updateBeatDistance();
-    qDebug() << getGroup() << "beat distance updated" << beatDistance;
     m_pSyncControl->setLocalBpm(localBpm);
     m_pSyncControl->updateAudible();
     SyncMode mode = m_pSyncControl->getSyncMode();
diff --git a/src/engine/enginemaster.cpp b/src/engine/enginemaster.cpp
index cda9a1dbb51..202fe0b1341 100644
--- a/src/engine/enginemaster.cpp
+++ b/src/engine/enginemaster.cpp
@@ -369,11 +369,9 @@ void EngineMaster::processChannels(int iBufferSize) {
 
     // Do internal master sync post-processing before the other
     // channels.
-    // OK, so this means the internal clock knows that it has crossed a beat
-    // boundary before the channels do. This means when we call this, we
-    // notify all the channels that the master beat distance has changed.
-    // They try to update the target beat distance, and guess the
-    // wrong number because they can't do half/double calculation correctly.
+    // Note, because we call this on the internal clock first,
+    // it will have an up-to-date beatDistance, whereas the other
+    // Syncables will not.
     m_pMasterSync->onCallbackEnd(m_iSampleRate, m_iBufferSize);
 
     // After all the engines have been processed, trigger post-processing
diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index f913eb8c73d..fad3c6ed696 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -96,15 +96,8 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    auto players = getPlayingSyncables();
-    if (players.size() == 1) {
-        qDebug() << "!!!!!!!!!!!!!!!!!!!!!1there is only one playing syncable, tell it so!";
-        players.at(0)->notifyOnlyPlayingSyncable();
-    } else {
-        qDebug() << "players!";
-        for (auto* play : players) {
-            qDebug() << play->getGroup();
-        }
+    if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
+        onlyPlayer->notifyOnlyPlayingSyncable();
     }
 }
 
@@ -358,30 +351,11 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
     if (newMaster != nullptr && newMaster != m_pMasterSyncable) {
         activateMaster(newMaster, SYNC_MASTER_SOFT);
         setMasterParams(newMaster);
-    }
-
-    // we know for a fact that pSyncable is playing and audible.
-    // We want to init master params
-    // cases:
-    // just we are playing: set master params with our settings
-    // NO. just because we are master, doesn't mean we win! we might be copying someone else.
-    // if anything we should JUST init beat distance.
-    // another deck is playing and it's master: don't touch it
-    // another deck is playing and it's not master: don't touch it
-    auto players = getPlayingSyncables();
-    if (players.size() == 1) {
-        Syncable* onlyPlayer = players.at(0);
-        qDebug() << "2222222222222222222222222222 there is only one playing "
-                    "syncable, it gets to set beat dist"
-                 << onlyPlayer->getGroup();
+    } else if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
+        // Even if we didn't change master, if there is only one player (us), then we should
+        // reinit the beat distance.
         onlyPlayer->notifyOnlyPlayingSyncable();
-        // setMasterParams(onlyPlayer);
         setMasterBeatDistance(onlyPlayer, onlyPlayer->getBeatDistance());
-    } else {
-        qDebug() << "players!";
-        for (auto* play : players) {
-            qDebug() << play->getGroup();
-        }
     }
 
     pSyncable->requestSync();
@@ -611,6 +585,11 @@ void EngineSync::setMasterInstantaneousBpm(Syncable* pSource, double bpm) {
 }
 
 void EngineSync::setMasterBeatDistance(Syncable* pSource, double beatDistance) {
+    if (kLogger.traceEnabled()) {
+        kLogger.trace() << "EngineSync::setMasterBeatDistance"
+                        << (pSource ? pSource->getGroup() : "null")
+                        << beatDistance;
+    }
     if (pSource != m_pInternalClock) {
         m_pInternalClock->setMasterBeatDistance(beatDistance);
     }
@@ -624,55 +603,47 @@ void EngineSync::setMasterBeatDistance(Syncable* pSource, double beatDistance) {
 }
 
 void EngineSync::setMasterParams(Syncable* pSource) {
-    // so the bug here is that we are setting the master parameters from some source, but
-    // that source may not be the master! but when we update the multipliers, we update
-    // based on who is master. We used to try to force master to be multiplier 1.0, but that
-    // causes problems.
-
+    // Important note! Because of the way sync works, the new master is usually not the same
+    // as the Syncable setting the master parameters (here, pSource). Notify the proper Syncable
+    // so it can prepare itself.  (This is a hack to undo half/double math so that we initialize
+    // based on un-multiplied bpm values).
     pSource->notifyMasterParamSource();
 
     double beatDistance = pSource->getBeatDistance();
-    // // If the params source is not playing, but other syncables are, then we are a stopped
-    // // explicit Master and we should not initialize the beat distance.  Take it from the
-    // // internal clock instead.
     if (!pSource->isPlaying()) {
+        // If the params source is not playing, but other syncables are, then we are a stopped
+        // explicit Master and we should not initialize the beat distance.  Take it from the
+        // internal clock instead.
         bool playingSyncables = false;
         for (Syncable* pSyncable : m_syncables) {
-            qDebug() << "checking" << pSyncable->getGroup();
             if (pSyncable == pSource) {
                 continue;
             }
             if (!pSyncable->isSynchronized()) {
                 continue;
             }
-            qDebug() << "it's valid";
             if (pSyncable->isPlaying()) {
-                qDebug() << "found a playing syncable" << pSyncable->getGroup();
                 playingSyncables = true;
                 break;
             }
         }
         if (playingSyncables) {
-            qDebug() << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
-                        "BaseSyncableListener::setMasterParams, not playing, "
-                        "playing followers, pull from internal clock"
-                     << pSource->getGroup();
             beatDistance = m_pInternalClock->getBeatDistance();
         }
     }
-    // Do we want the RAW values here, not multiplied by adjust factor??
     const double baseBpm = pSource->getBaseBpm();
     double bpm = pSource->getBpm();
     if (bpm <= 0) {
         bpm = baseBpm;
     }
-    qDebug() << "BaseSyncableListener::setMasterParams, source is"
-             << pSource->getGroup() << beatDistance << baseBpm << bpm;
+    if (kLogger.traceEnabled()) {
+        kLogger.trace() << "BaseSyncableListener::setMasterParams, source is"
+                        << pSource->getGroup() << beatDistance << baseBpm << bpm;
+    }
     if (pSource != m_pInternalClock) {
         m_pInternalClock->setMasterParams(beatDistance, baseBpm, bpm);
     }
     foreach (Syncable* pSyncable, m_syncables) {
-        // not sure if we should skip the pSource here.
         if (!pSyncable->isSynchronized()) {
             continue;
         }
@@ -680,16 +651,20 @@ void EngineSync::setMasterParams(Syncable* pSource) {
     }
 }
 
-QList<Syncable*> EngineSync::getPlayingSyncables() const {
-    QList<Syncable*> players;
+Syncable* EngineSync::getOnlyPlayingSyncable() const {
+    Syncable* onlyPlaying = nullptr;
     for (Syncable* pSyncable : m_syncables) {
         if (!pSyncable->isSynchronized()) {
             continue;
         }
 
         if (pSyncable->isPlaying()) {
-            players.append(pSyncable);
+            if (!onlyPlaying) {
+                onlyPlaying = pSyncable;
+            } else {
+                return nullptr;
+            }
         }
     }
-    return players;
+    return onlyPlaying;
 }
diff --git a/src/engine/sync/enginesync.h b/src/engine/sync/enginesync.h
index 8e306e14a91..4988a14c422 100644
--- a/src/engine/sync/enginesync.h
+++ b/src/engine/sync/enginesync.h
@@ -115,8 +115,9 @@ class EngineSync : public SyncableListener {
 
     void setMasterParams(Syncable* pSource);
 
-    /// Return the playing syncables, if any. This is used to initialize beat distance settings.
-    QList<Syncable*> getPlayingSyncables() const;
+    /// Iff there is a single playing syncable, return it. This is used to initialize master
+    /// params.
+    Syncable* getOnlyPlayingSyncable() const;
 
     /// Only for testing. Do not use.
     Syncable* getSyncableForGroup(const QString& group);
diff --git a/src/engine/sync/syncable.h b/src/engine/sync/syncable.h
index 19678be6229..fa29b1da915 100644
--- a/src/engine/sync/syncable.h
+++ b/src/engine/sync/syncable.h
@@ -114,7 +114,7 @@ class Syncable {
 
     // Tells a Syncable that it's going to be used as a source for master
     // params. This is a gross hack so that the SyncControl can undo its
-    // half/double adjustment.
+    // half/double adjustment so bpms are initialized correctly.
     virtual void notifyMasterParamSource() = 0;
 
     // Combines the above three calls into one, since they are often set
diff --git a/src/engine/sync/synccontrol.cpp b/src/engine/sync/synccontrol.cpp
index 9c9a3c0b9d0..d387a22488c 100644
--- a/src/engine/sync/synccontrol.cpp
+++ b/src/engine/sync/synccontrol.cpp
@@ -212,7 +212,6 @@ void SyncControl::setMasterBeatDistance(double beatDistance) {
     // Set the BpmControl target beat distance to beatDistance, adjusted by
     // the multiplier if in effect.  This way all of the multiplier logic
     // is contained in this single class.
-    m_lastTargetBeatDistance = m_unmultipliedTargetBeatDistance;
     m_unmultipliedTargetBeatDistance = beatDistance;
     // Update the target beat distance based on the multiplier.
     updateTargetBeatDistance();
@@ -245,31 +244,11 @@ void SyncControl::notifyMasterParamSource() {
 
 void SyncControl::setMasterParams(
         double beatDistance, double baseBpm, double bpm) {
-    qDebug() << "SyncControl::setMasterParams" << getGroup() << beatDistance << baseBpm << bpm;
-    // if (paramSource == this) {
-    //     baseBpm *= m_masterBpmAdjustFactor;
-    //     bpm *= m_masterBpmAdjustFactor;
-    //     qDebug() << "we were param source, undo adjust factor:" << baseBpm << bpm;
-    // }
-    // Calculate the factor for the file bpm. That gives the best
-    // result at any rate slider position.
-    qDebug() << "file bpm: " << fileBpm();
-
-    // masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    // double masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    if (kLogger.traceEnabled()) {
+        kLogger.trace() << "SyncControl::setMasterParams" << getGroup()
+                        << beatDistance << baseBpm << bpm;
+    }
     m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    // if (paramSource == this) {
-    //     //     qDebug() << "We were param source!";
-    //     //     // If we are the param source, we need to undo the adjustment factor
-    //     //     // or else we start piling multipliers on top of each other.
-    //     //     bpm *= masterBpmAdjustFactor;
-    //     m_masterBpmAdjustFactor = kBpmUnity;
-    // } else {
-    //     m_masterBpmAdjustFactor = masterBpmAdjustFactor;
-    // }
-
-    // m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    qDebug() << "ADJUST FACTOR?!" << m_masterBpmAdjustFactor;
     setMasterBpm(bpm);
     setMasterBeatDistance(beatDistance);
 }
@@ -311,7 +290,6 @@ void SyncControl::updateTargetBeatDistance() {
         targetDistance *= kBpmDouble;
     } else if (m_masterBpmAdjustFactor == kBpmHalve) {
         targetDistance *= kBpmHalve;
-        qDebug() << "my beat dist" << m_pBeatDistance->get();
         // Our beat distance CO is still a buffer behind, so take the current value.
         if (m_pBpmControl->getBeatDistance(getSampleOfTrack().current) >= 0.5) {
             targetDistance += 0.5;
@@ -466,7 +444,6 @@ void SyncControl::setLocalBpm(double local_bpm) {
     if (local_bpm == m_prevLocalBpm.getValue()) {
         return;
     }
-    qDebug() << "SyncControl::setLocalBpm" << getGroup() << local_bpm;
     m_prevLocalBpm.setValue(local_bpm);
 
     SyncMode syncMode = getSyncMode();
diff --git a/src/engine/sync/synccontrol.h b/src/engine/sync/synccontrol.h
index 32781b42ff3..357106fca94 100644
--- a/src/engine/sync/synccontrol.h
+++ b/src/engine/sync/synccontrol.h
@@ -113,7 +113,6 @@ class SyncControl : public EngineControl, public Syncable {
     // It is handy to store the raw reported target beat distance in case the
     // multiplier changes and we need to recalculate the target distance.
     double m_unmultipliedTargetBeatDistance;
-    double m_lastTargetBeatDistance;
     ControlValueAtomic<double> m_prevLocalBpm;
     QAtomicInt m_audible;
 
diff --git a/src/test/enginesynctest.cpp b/src/test/enginesynctest.cpp
index 39a216db188..66351320754 100644
--- a/src/test/enginesynctest.cpp
+++ b/src/test/enginesynctest.cpp
@@ -1445,6 +1445,23 @@ TEST_F(EngineSyncTest, ZeroBPMRateAdjustIgnored) {
             ControlObject::getControl(ConfigKey(m_sGroup2, "rate"))->get());
 }
 
+TEST_F(EngineSyncTest, DISABLED_BeatDistanceBeforeStart) {
+    // If the start position is before zero, we should still initialize the beat distance
+    // corretly.  Unfortunately, this currently doesn't work.
+
+    mixxx::BeatsPointer pBeats1 = BeatFactory::makeBeatGrid(m_pTrack1->getSampleRate(), 128, 0.0);
+    m_pTrack1->trySetBeats(pBeats1);
+    ControlObject::set(ConfigKey(m_sGroup1, "playposition"), -.05);
+    ControlObject::getControl(ConfigKey(m_sGroup1, "sync_mode"))
+            ->set(SYNC_MASTER_SOFT);
+    ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
+    ProcessBuffer();
+    EXPECT_NEAR(
+            ControlObject::getControl(ConfigKey(m_sGroup1, "beat_distance"))->get(),
+            ControlObject::getControl(ConfigKey(m_sInternalClockGroup, "beat_distance"))->get(),
+            kMaxBeatDistanceEpsilon);
+}
+
 TEST_F(EngineSyncTest, ZeroLatencyRateChangeNoQuant) {
     // Confirm that a rate change in an explicit master is instantly communicated
     // to followers.
@@ -1660,9 +1677,7 @@ TEST_F(EngineSyncTest, HalfDoubleBpmTest) {
             ->set(SYNC_FOLLOWER);
 
     // Mixxx will choose the first playing deck to be master.  Let's start deck 2 first.
-    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch2 play";
     ControlObject::getControl(ConfigKey(m_sGroup2, "play"))->set(1.0);
-    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch1 play";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
     ProcessBuffer();
 
@@ -1999,9 +2014,7 @@ TEST_F(EngineSyncTest, SyncPhaseToPlayingNonSyncDeck) {
     // Next Deck becomes master and the Master clock is set to 100 BPM
     // The 130 BPM Track should be played at 100 BPM, rate = 0.769230769
     pButtonSyncEnabled1->set(1.0);
-    qDebug() << "PUSH PLAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAY";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
-
     // Beat length: 40707.692307692305
     // Buffer size is 1024 at 44.1 kHz at the given rate = 787.692307692 Samples
     // Expected beat_distance = 0.019349962

From c52160167664dca0f08e4734b62bd44546004daa Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Fri, 28 May 2021 18:53:48 -0400
Subject: [PATCH 03/22] Sync Lock: Fix clazy issue

---
 src/engine/sync/enginesync.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index fad3c6ed696..1b8e876e010 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -615,7 +615,7 @@ void EngineSync::setMasterParams(Syncable* pSource) {
         // explicit Master and we should not initialize the beat distance.  Take it from the
         // internal clock instead.
         bool playingSyncables = false;
-        for (Syncable* pSyncable : m_syncables) {
+        for (Syncable* pSyncable : qAsConst(m_syncables)) {
             if (pSyncable == pSource) {
                 continue;
             }

From 15cd3d402e0037a7a9221d45431841645ce53cf3 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Sat, 29 May 2021 13:35:39 -0400
Subject: [PATCH 04/22] sync lock: add bug link for disabled / broken test

---
 src/test/enginesynctest.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/test/enginesynctest.cpp b/src/test/enginesynctest.cpp
index 66351320754..953c9405e62 100644
--- a/src/test/enginesynctest.cpp
+++ b/src/test/enginesynctest.cpp
@@ -1446,8 +1446,9 @@ TEST_F(EngineSyncTest, ZeroBPMRateAdjustIgnored) {
 }
 
 TEST_F(EngineSyncTest, DISABLED_BeatDistanceBeforeStart) {
+    // https://bugs.launchpad.net/mixxx/+bug/1930143
     // If the start position is before zero, we should still initialize the beat distance
-    // corretly.  Unfortunately, this currently doesn't work.
+    // correctly.  Unfortunately, this currently doesn't work.
 
     mixxx::BeatsPointer pBeats1 = BeatFactory::makeBeatGrid(m_pTrack1->getSampleRate(), 128, 0.0);
     m_pTrack1->trySetBeats(pBeats1);

From 35ed9c9470ac4711776fb03c2b0c98a3e319d545 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Mon, 31 May 2021 22:58:19 -0400
Subject: [PATCH 05/22] Sync Lock: don't use c++17 inline conditional
 assignment (1)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Daniel Schürmann <daschuer@mixxx.org>
---
 src/engine/sync/enginesync.cpp | 22 +++++++++++++---------
 src/engine/sync/enginesync.h   |  6 +++---
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 1b8e876e010..f187d8b20bd 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -96,8 +96,9 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
-        onlyPlayer->notifyOnlyPlayingSyncable();
+    Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
+    if (pOnlyPlayer) {
+        pOnlyPlayer->notifyOnlyPlayingSyncable();
     }
 }
 
@@ -351,11 +352,14 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
     if (newMaster != nullptr && newMaster != m_pMasterSyncable) {
         activateMaster(newMaster, SYNC_MASTER_SOFT);
         setMasterParams(newMaster);
-    } else if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
-        // Even if we didn't change master, if there is only one player (us), then we should
-        // reinit the beat distance.
-        onlyPlayer->notifyOnlyPlayingSyncable();
-        setMasterBeatDistance(onlyPlayer, onlyPlayer->getBeatDistance());
+    } else {
+        Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
+        if (pOnlyPlayer) {
+            // Even if we didn't change master, if there is only one player (us), then we should
+            // reinit the beat distance.
+            pOnlyPlayer->notifyOnlyPlayingSyncable();
+            setMasterBeatDistance(pOnlyPlayer, pOnlyPlayer->getBeatDistance());
+        }
     }
 
     pSyncable->requestSync();
@@ -613,7 +617,7 @@ void EngineSync::setMasterParams(Syncable* pSource) {
     if (!pSource->isPlaying()) {
         // If the params source is not playing, but other syncables are, then we are a stopped
         // explicit Master and we should not initialize the beat distance.  Take it from the
-        // internal clock instead.
+        // internal clock instead, because that will be up to date with the playing deck(s).
         bool playingSyncables = false;
         for (Syncable* pSyncable : qAsConst(m_syncables)) {
             if (pSyncable == pSource) {
@@ -651,7 +655,7 @@ void EngineSync::setMasterParams(Syncable* pSource) {
     }
 }
 
-Syncable* EngineSync::getOnlyPlayingSyncable() const {
+Syncable* EngineSync::getUniquePlayingSyncedDeck() const {
     Syncable* onlyPlaying = nullptr;
     for (Syncable* pSyncable : m_syncables) {
         if (!pSyncable->isSynchronized()) {
diff --git a/src/engine/sync/enginesync.h b/src/engine/sync/enginesync.h
index 4988a14c422..5ce7574b520 100644
--- a/src/engine/sync/enginesync.h
+++ b/src/engine/sync/enginesync.h
@@ -115,9 +115,9 @@ class EngineSync : public SyncableListener {
 
     void setMasterParams(Syncable* pSource);
 
-    /// Iff there is a single playing syncable, return it. This is used to initialize master
-    /// params.
-    Syncable* getOnlyPlayingSyncable() const;
+    /// Iff there is a single playing syncable in sync mode, return it.
+    /// This is used to initialize master params.
+    Syncable* getUniquePlayingSyncedDeck() const;
 
     /// Only for testing. Do not use.
     Syncable* getSyncableForGroup(const QString& group);

From ec01df82b8b8324014dd02a663470229f5965328 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Mon, 31 May 2021 23:32:29 -0400
Subject: [PATCH 06/22] Sync Lock: Fix issue where single playing sync deck was
 syncing against its nudge value

---
 src/engine/sync/enginesync.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index f187d8b20bd..2e7a5bec784 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -75,6 +75,13 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
     default:;
     }
 
+    Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
+    if (pOnlyPlayer) {
+        // This resets the user offset, so that if this deck gets used as the params syncable
+        // it will have that offset removed.
+        pOnlyPlayer->notifyOnlyPlayingSyncable();
+    }
+
     // Second, figure out what Syncable should be used to initialize the master
     // parameters, if any. Usually this is the new master. (Note, that pointer might be null!)
     Syncable* pParamsSyncable = m_pMasterSyncable;
@@ -96,10 +103,6 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
-    if (pOnlyPlayer) {
-        pOnlyPlayer->notifyOnlyPlayingSyncable();
-    }
 }
 
 void EngineSync::activateFollower(Syncable* pSyncable) {

From b041a6ea33f52a13bded6c70e9c9ba8514a2f82e Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 14:20:25 -0400
Subject: [PATCH 07/22] Sync Lock: better name for function

---
 src/engine/sync/enginesync.cpp    | 4 ++--
 src/engine/sync/internalclock.cpp | 2 +-
 src/engine/sync/internalclock.h   | 2 +-
 src/engine/sync/syncable.h        | 2 +-
 src/engine/sync/synccontrol.cpp   | 2 +-
 src/engine/sync/synccontrol.h     | 2 +-
 6 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 2e7a5bec784..474ff418e99 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -79,7 +79,7 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
     if (pOnlyPlayer) {
         // This resets the user offset, so that if this deck gets used as the params syncable
         // it will have that offset removed.
-        pOnlyPlayer->notifyOnlyPlayingSyncable();
+        pOnlyPlayer->notifyUniquePlaying();
     }
 
     // Second, figure out what Syncable should be used to initialize the master
@@ -360,7 +360,7 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
         if (pOnlyPlayer) {
             // Even if we didn't change master, if there is only one player (us), then we should
             // reinit the beat distance.
-            pOnlyPlayer->notifyOnlyPlayingSyncable();
+            pOnlyPlayer->notifyUniquePlaying();
             setMasterBeatDistance(pOnlyPlayer, pOnlyPlayer->getBeatDistance());
         }
     }
diff --git a/src/engine/sync/internalclock.cpp b/src/engine/sync/internalclock.cpp
index 8c3731f2397..734523d7e83 100644
--- a/src/engine/sync/internalclock.cpp
+++ b/src/engine/sync/internalclock.cpp
@@ -60,7 +60,7 @@ void InternalClock::setSyncMode(SyncMode mode) {
     m_pSyncMasterEnabled->setAndConfirm(SyncModeToMasterLight(mode));
 }
 
-void InternalClock::notifyOnlyPlayingSyncable() {
+void InternalClock::notifyUniquePlaying() {
     // No action necessary.
 }
 
diff --git a/src/engine/sync/internalclock.h b/src/engine/sync/internalclock.h
index dea03a490d7..da0ddde7509 100644
--- a/src/engine/sync/internalclock.h
+++ b/src/engine/sync/internalclock.h
@@ -32,7 +32,7 @@ class InternalClock : public QObject, public Clock, public Syncable {
     }
 
     void setSyncMode(SyncMode mode) override;
-    void notifyOnlyPlayingSyncable() override;
+    void notifyUniquePlaying() override;
     void requestSync() override;
     SyncMode getSyncMode() const override {
         return m_mode;
diff --git a/src/engine/sync/syncable.h b/src/engine/sync/syncable.h
index fa29b1da915..1596b378cbb 100644
--- a/src/engine/sync/syncable.h
+++ b/src/engine/sync/syncable.h
@@ -76,7 +76,7 @@ class Syncable {
     virtual void setSyncMode(SyncMode mode) = 0;
 
     // Notify a Syncable that it is now the only currently-playing syncable.
-    virtual void notifyOnlyPlayingSyncable() = 0;
+    virtual void notifyUniquePlaying() = 0;
 
     // Notify a Syncable that they should sync phase.
     virtual void requestSync() = 0;
diff --git a/src/engine/sync/synccontrol.cpp b/src/engine/sync/synccontrol.cpp
index d387a22488c..728a51d9b39 100644
--- a/src/engine/sync/synccontrol.cpp
+++ b/src/engine/sync/synccontrol.cpp
@@ -145,7 +145,7 @@ void SyncControl::setSyncMode(SyncMode mode) {
     }
 }
 
-void SyncControl::notifyOnlyPlayingSyncable() {
+void SyncControl::notifyUniquePlaying() {
     // If we are the only remaining playing sync deck, we can reset the user
     // tweak info.
     m_pBpmControl->resetSyncAdjustment();
diff --git a/src/engine/sync/synccontrol.h b/src/engine/sync/synccontrol.h
index 357106fca94..69af12e6c65 100644
--- a/src/engine/sync/synccontrol.h
+++ b/src/engine/sync/synccontrol.h
@@ -30,7 +30,7 @@ class SyncControl : public EngineControl, public Syncable {
 
     SyncMode getSyncMode() const override;
     void setSyncMode(SyncMode mode) override;
-    void notifyOnlyPlayingSyncable() override;
+    void notifyUniquePlaying() override;
     void requestSync() override;
     bool isPlaying() const override;
     bool isAudible() const override;

From d8c843a676391f2f7d405dc19c81e7d9c6da74ae Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 15:05:54 -0400
Subject: [PATCH 08/22] SyncLock: Increase deck size to make room for Leader
 button

---
 res/skins/LateNight/decks/deck.xml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/res/skins/LateNight/decks/deck.xml b/res/skins/LateNight/decks/deck.xml
index 9c42c500528..7f6d1228641 100644
--- a/res/skins/LateNight/decks/deck.xml
+++ b/res/skins/LateNight/decks/deck.xml
@@ -2,7 +2,7 @@
 
   <WidgetGroup>
     <Layout>vertical</Layout>
-    <MaximumSize>,208</MaximumSize>
+    <MaximumSize>,230</MaximumSize>
     <Children>
 
       <Template src="skin:/decks/deck_singletons.xml">

From ae18e4e22c4254a62b26a44c59a192b5aebecc21 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 15:06:54 -0400
Subject: [PATCH 09/22] SyncLock: Fix leader button in latenight classic

---
 res/skins/LateNight/style_classic.qss | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/res/skins/LateNight/style_classic.qss b/res/skins/LateNight/style_classic.qss
index 17b4245e85a..ea4a6d214e0 100644
--- a/res/skins/LateNight/style_classic.qss
+++ b/res/skins/LateNight/style_classic.qss
@@ -1662,7 +1662,7 @@ WPushButton#SamplerExpand[displayValue="0"],
   }
 
 #SyncLeader {
-  background: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
+  image: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
   }
 
   #SyncSampler {

From 0e03653a6d004035534fa660080e4d7ecc7cb997 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 16:52:41 -0400
Subject: [PATCH 10/22] SyncLock: Skin fixes

---
 .../palemoon/buttons/btn__leader_deck.svg     | 87 +++++++++++++++++++
 res/skins/LateNight/style_classic.qss         |  2 +-
 res/skins/LateNight/style_palemoon.qss        |  8 +-
 3 files changed, 95 insertions(+), 2 deletions(-)
 create mode 100644 res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg

diff --git a/res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg b/res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg
new file mode 100644
index 00000000000..7f7de5bf879
--- /dev/null
+++ b/res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg
@@ -0,0 +1,87 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   width="46"
+   height="20"
+   version="1.1"
+   id="svg32"
+   sodipodi:docname="btn__leader_deck.svg"
+   inkscape:version="0.92.5 (2060ec1f9f, 2020-04-08)">
+  <metadata
+     id="metadata38">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <defs
+     id="defs36" />
+  <sodipodi:namedview
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1"
+     objecttolerance="10"
+     gridtolerance="10"
+     guidetolerance="10"
+     inkscape:pageopacity="0"
+     inkscape:pageshadow="2"
+     inkscape:window-width="1920"
+     inkscape:window-height="1017"
+     id="namedview34"
+     showgrid="true"
+     inkscape:zoom="16"
+     inkscape:cx="23.740955"
+     inkscape:cy="16.667631"
+     inkscape:window-x="0"
+     inkscape:window-y="26"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg32">
+    <inkscape:grid
+       type="xygrid"
+       id="grid854" />
+  </sodipodi:namedview>
+  <g
+     id="g10"
+     style="display:inline;fill:none"
+     transform="translate(-2,-2)">
+    <path
+       d="M 16,8 H 9 v 4 h 5 v 2 H 9 v 1 h 7 V 11 H 11 V 9 h 5 V 8"
+       id="path2"
+       inkscape:connector-curvature="0" />
+    <path
+       d="m 26,8 v 7 h 2 V 9 h 3 v 6 h 2 V 8 h -7"
+       id="path4"
+       inkscape:connector-curvature="0" />
+    <path
+       d="m 34,8 v 7 h 7 V 14 H 36 V 9 h 5 V 8 h -7"
+       id="path6"
+       inkscape:connector-curvature="0" />
+    <path
+       d="m 20,15 v -3.5 l -3,-3 V 8 h 1.5 L 21,10.5 23.5,8 H 25 v 0.5 l -3,3 V 15 h -2"
+       id="path8"
+       inkscape:connector-curvature="0" />
+  </g>
+  <text
+     xml:space="preserve"
+     style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:11.27830696px;line-height:0%;font-family:'Latina Essential';-inkscape-font-specification:'Latina Essential';writing-mode:lr-tb;opacity:1;fill:#d2d2d1;fill-opacity:1;stroke:#000000;stroke-width:0.84600008;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1"
+     x="0.056735612"
+     y="14.086957"
+     id="text4532"
+     transform="scale(1.0060601,0.99397642)"><tspan
+       sodipodi:role="line"
+       id="tspan4530"
+       x="0.056735612"
+       y="14.086957"
+       style="stroke-width:0.84600008">LEADER</tspan></text>
+</svg>
diff --git a/res/skins/LateNight/style_classic.qss b/res/skins/LateNight/style_classic.qss
index ea4a6d214e0..20c25f1844b 100644
--- a/res/skins/LateNight/style_classic.qss
+++ b/res/skins/LateNight/style_classic.qss
@@ -1314,7 +1314,7 @@ WPushButton#PlayIndicator,
 WPushButton#CueDeck,
 #PlayCueMini WPushButton,
 WPushButton#LoopActivate,
-#RateControls WPushButton,
+WPushButton#RateControls WPushButton,
 WPushButton#SyncDeck,
 WPushButton#SyncLeader,
 WPushButton#SyncSampler,
diff --git a/res/skins/LateNight/style_palemoon.qss b/res/skins/LateNight/style_palemoon.qss
index 4df0ee6c349..5063fc8b428 100644
--- a/res/skins/LateNight/style_palemoon.qss
+++ b/res/skins/LateNight/style_palemoon.qss
@@ -1522,7 +1522,9 @@ WPushButton#CueDeck,
 #PlayCueMini WPushButton,
 WPushButton#LoopActivate,
 WPushButton#RateControls WPushButton,
-WPushButton#SyncDeck, WPushButton#SyncSampler,
+WPushButton#SyncDeck,
+WPushButton#SyncLeader,
+WPushButton#SyncSampler,
 #MixerContainer WPushButton,
 #FxUnitContainer WPushButton,
 #Sampler WPushButton,
@@ -2105,6 +2107,10 @@ WPushButton#PlayDeck[value="0"] {
     image: url(skin:/palemoon/buttons/btn__sync_deck_active.svg) no-repeat center center;
   }
 
+#SyncLeader {
+  image: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
+  }
+
   #SyncSampler {
     image: url(skin:/palemoon/buttons/btn__sync_sampler.svg) no-repeat center center;
     }

From 58d0e4b01edeaf475a064944297e614b91708c80 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 23:50:51 -0400
Subject: [PATCH 11/22] Sync Lock: Fix Leader button colors

---
 res/skins/LateNight/style_classic.qss  | 9 ++++++++-
 res/skins/LateNight/style_palemoon.qss | 6 ++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/res/skins/LateNight/style_classic.qss b/res/skins/LateNight/style_classic.qss
index 20c25f1844b..47dfad05a57 100644
--- a/res/skins/LateNight/style_classic.qss
+++ b/res/skins/LateNight/style_classic.qss
@@ -1378,10 +1378,17 @@ WPushButton#SkinSettingsToggle[displayValue="0"] {
   background-color: #262626;
 }
 
+/* Orange for 'partially active' status */
+#SyncLeader[value="1"] {
+background-color: #db7700;
+}
+
 /* Red for 'active' status */
 #BeatgridControls WPushButton[value="1"],
 #RateControls WPushButton[value="1"],
-#SyncDeck[value="1"], #SyncSampler[displayValue="1"],
+#SyncDeck[value="1"],
+#SyncLeader[value="2"],
+#SyncSampler[displayValue="1"],
 WPushButton#PlayDeck[displayValue="1"],
 WPushButton#PlayDeckMini[displayValue="1"],
 WPushButton#PlaySampler[displayValue="1"],
diff --git a/res/skins/LateNight/style_palemoon.qss b/res/skins/LateNight/style_palemoon.qss
index 5063fc8b428..0866164d5c6 100644
--- a/res/skins/LateNight/style_palemoon.qss
+++ b/res/skins/LateNight/style_palemoon.qss
@@ -1635,6 +1635,8 @@ WPushButton#Reverse[pressed="true"],
 #LoopActivate[value="1"],
 #Reloop[value="1"],
 #SyncSampler[displayValue="1"],
+#SyncDeck[value="1"],
+#SyncLeader[value="2"],
 #MicTalk[value="1"], #AuxPlay[value="1"],
 #MicDucking[value="1"],
 #MicDucking[value="2"],
@@ -1653,7 +1655,7 @@ QPushButton#pushButtonAnalyze:checked {
   }
 /* dim orange for momentary controls */
 #KeyControls WPushButton[pressed="true"],
-#SyncDeck[value="1"],
+#SyncLeader[value="1"],
 WPushButton#LoopIn[pressed="true"],
 WPushButton#LoopOut[pressed="true"],
 #BeatjumpControls WPushButton[value="1"],
@@ -2108,7 +2110,7 @@ WPushButton#PlayDeck[value="0"] {
   }
 
 #SyncLeader {
-  image: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
+  image: url(skin:/palemoon/buttons/btn__leader_deck.svg) no-repeat center center;
   }
 
   #SyncSampler {

From 534eacfeaa080e16caa57bdfb916cbe350d66013 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Sun, 23 May 2021 13:44:10 -0400
Subject: [PATCH 12/22] Fix half-double initialization issues

---
 src/engine/enginebuffer.cpp       |  1 +
 src/engine/enginemaster.cpp       |  5 ++
 src/engine/sync/enginesync.cpp    | 96 +++++++++++++++++++++++++------
 src/engine/sync/enginesync.h      |  4 +-
 src/engine/sync/internalclock.cpp |  3 +
 src/engine/sync/internalclock.h   |  1 +
 src/engine/sync/syncable.h        |  5 ++
 src/engine/sync/synccontrol.cpp   | 50 ++++++++++++----
 src/engine/sync/synccontrol.h     |  3 +-
 src/test/enginesynctest.cpp       | 15 +++--
 10 files changed, 147 insertions(+), 36 deletions(-)

diff --git a/src/engine/enginebuffer.cpp b/src/engine/enginebuffer.cpp
index 80065ba2b25..4a5d011d40b 100644
--- a/src/engine/enginebuffer.cpp
+++ b/src/engine/enginebuffer.cpp
@@ -1297,6 +1297,7 @@ void EngineBuffer::postProcess(const int iBufferSize) {
     }
     double localBpm = m_pBpmControl->updateLocalBpm();
     double beatDistance = m_pBpmControl->updateBeatDistance();
+    qDebug() << getGroup() << "beat distance updated" << beatDistance;
     m_pSyncControl->setLocalBpm(localBpm);
     m_pSyncControl->updateAudible();
     SyncMode mode = m_pSyncControl->getSyncMode();
diff --git a/src/engine/enginemaster.cpp b/src/engine/enginemaster.cpp
index 33cd29d5e42..cda9a1dbb51 100644
--- a/src/engine/enginemaster.cpp
+++ b/src/engine/enginemaster.cpp
@@ -369,6 +369,11 @@ void EngineMaster::processChannels(int iBufferSize) {
 
     // Do internal master sync post-processing before the other
     // channels.
+    // OK, so this means the internal clock knows that it has crossed a beat
+    // boundary before the channels do. This means when we call this, we
+    // notify all the channels that the master beat distance has changed.
+    // They try to update the target beat distance, and guess the
+    // wrong number because they can't do half/double calculation correctly.
     m_pMasterSync->onCallbackEnd(m_iSampleRate, m_iBufferSize);
 
     // After all the engines have been processed, trigger post-processing
diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 7602283d22d..f913eb8c73d 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -96,8 +96,15 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    if (noPlayingFollowers() && m_pMasterSyncable) {
-        m_pMasterSyncable->notifyOnlyPlayingSyncable();
+    auto players = getPlayingSyncables();
+    if (players.size() == 1) {
+        qDebug() << "!!!!!!!!!!!!!!!!!!!!!1there is only one playing syncable, tell it so!";
+        players.at(0)->notifyOnlyPlayingSyncable();
+    } else {
+        qDebug() << "players!";
+        for (auto* play : players) {
+            qDebug() << play->getGroup();
+        }
     }
 }
 
@@ -350,11 +357,31 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
 
     if (newMaster != nullptr && newMaster != m_pMasterSyncable) {
         activateMaster(newMaster, SYNC_MASTER_SOFT);
-    }
-
-    if (noPlayingFollowers() && m_pMasterSyncable) {
-        m_pMasterSyncable->notifyOnlyPlayingSyncable();
-        setMasterParams(m_pMasterSyncable);
+        setMasterParams(newMaster);
+    }
+
+    // we know for a fact that pSyncable is playing and audible.
+    // We want to init master params
+    // cases:
+    // just we are playing: set master params with our settings
+    // NO. just because we are master, doesn't mean we win! we might be copying someone else.
+    // if anything we should JUST init beat distance.
+    // another deck is playing and it's master: don't touch it
+    // another deck is playing and it's not master: don't touch it
+    auto players = getPlayingSyncables();
+    if (players.size() == 1) {
+        Syncable* onlyPlayer = players.at(0);
+        qDebug() << "2222222222222222222222222222 there is only one playing "
+                    "syncable, it gets to set beat dist"
+                 << onlyPlayer->getGroup();
+        onlyPlayer->notifyOnlyPlayingSyncable();
+        // setMasterParams(onlyPlayer);
+        setMasterBeatDistance(onlyPlayer, onlyPlayer->getBeatDistance());
+    } else {
+        qDebug() << "players!";
+        for (auto* play : players) {
+            qDebug() << play->getGroup();
+        }
     }
 
     pSyncable->requestSync();
@@ -597,35 +624,72 @@ void EngineSync::setMasterBeatDistance(Syncable* pSource, double beatDistance) {
 }
 
 void EngineSync::setMasterParams(Syncable* pSource) {
-    const double beatDistance = pSource->getBeatDistance();
+    // so the bug here is that we are setting the master parameters from some source, but
+    // that source may not be the master! but when we update the multipliers, we update
+    // based on who is master. We used to try to force master to be multiplier 1.0, but that
+    // causes problems.
+
+    pSource->notifyMasterParamSource();
+
+    double beatDistance = pSource->getBeatDistance();
+    // // If the params source is not playing, but other syncables are, then we are a stopped
+    // // explicit Master and we should not initialize the beat distance.  Take it from the
+    // // internal clock instead.
+    if (!pSource->isPlaying()) {
+        bool playingSyncables = false;
+        for (Syncable* pSyncable : m_syncables) {
+            qDebug() << "checking" << pSyncable->getGroup();
+            if (pSyncable == pSource) {
+                continue;
+            }
+            if (!pSyncable->isSynchronized()) {
+                continue;
+            }
+            qDebug() << "it's valid";
+            if (pSyncable->isPlaying()) {
+                qDebug() << "found a playing syncable" << pSyncable->getGroup();
+                playingSyncables = true;
+                break;
+            }
+        }
+        if (playingSyncables) {
+            qDebug() << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
+                        "BaseSyncableListener::setMasterParams, not playing, "
+                        "playing followers, pull from internal clock"
+                     << pSource->getGroup();
+            beatDistance = m_pInternalClock->getBeatDistance();
+        }
+    }
+    // Do we want the RAW values here, not multiplied by adjust factor??
     const double baseBpm = pSource->getBaseBpm();
     double bpm = pSource->getBpm();
     if (bpm <= 0) {
         bpm = baseBpm;
     }
-    // qDebug() << "BaseSyncableListener::setMasterParams, source is"
-    //          << pSource->getGroup() << beatDistance << baseBpm << bpm;
+    qDebug() << "BaseSyncableListener::setMasterParams, source is"
+             << pSource->getGroup() << beatDistance << baseBpm << bpm;
     if (pSource != m_pInternalClock) {
         m_pInternalClock->setMasterParams(beatDistance, baseBpm, bpm);
     }
     foreach (Syncable* pSyncable, m_syncables) {
-        if (pSyncable == pSource || !pSyncable->isSynchronized()) {
+        // not sure if we should skip the pSource here.
+        if (!pSyncable->isSynchronized()) {
             continue;
         }
         pSyncable->setMasterParams(beatDistance, baseBpm, bpm);
     }
 }
 
-bool EngineSync::noPlayingFollowers() const {
+QList<Syncable*> EngineSync::getPlayingSyncables() const {
+    QList<Syncable*> players;
     for (Syncable* pSyncable : m_syncables) {
         if (!pSyncable->isSynchronized()) {
             continue;
         }
 
-        if (pSyncable->isPlaying() && pSyncable->isAudible() &&
-                isFollower(pSyncable->getSyncMode())) {
-            return false;
+        if (pSyncable->isPlaying()) {
+            players.append(pSyncable);
         }
     }
-    return true;
+    return players;
 }
diff --git a/src/engine/sync/enginesync.h b/src/engine/sync/enginesync.h
index 426c5256f88..8e306e14a91 100644
--- a/src/engine/sync/enginesync.h
+++ b/src/engine/sync/enginesync.h
@@ -115,8 +115,8 @@ class EngineSync : public SyncableListener {
 
     void setMasterParams(Syncable* pSource);
 
-    /// Check if there are no playing followers left.
-    bool noPlayingFollowers() const;
+    /// Return the playing syncables, if any. This is used to initialize beat distance settings.
+    QList<Syncable*> getPlayingSyncables() const;
 
     /// Only for testing. Do not use.
     Syncable* getSyncableForGroup(const QString& group);
diff --git a/src/engine/sync/internalclock.cpp b/src/engine/sync/internalclock.cpp
index 8ecfe8b27ad..8c3731f2397 100644
--- a/src/engine/sync/internalclock.cpp
+++ b/src/engine/sync/internalclock.cpp
@@ -140,6 +140,9 @@ void InternalClock::setInstantaneousBpm(double bpm) {
     Q_UNUSED(bpm);
 }
 
+void InternalClock::notifyMasterParamSource() {
+}
+
 void InternalClock::setMasterParams(double beatDistance, double baseBpm, double bpm) {
     if (kLogger.traceEnabled()) {
         kLogger.trace() << "InternalClock::setMasterParams" << beatDistance << baseBpm << bpm;
diff --git a/src/engine/sync/internalclock.h b/src/engine/sync/internalclock.h
index 88ecfb38c6f..dea03a490d7 100644
--- a/src/engine/sync/internalclock.h
+++ b/src/engine/sync/internalclock.h
@@ -52,6 +52,7 @@ class InternalClock : public QObject, public Clock, public Syncable {
 
     double getBaseBpm() const override;
     void setMasterBpm(double bpm) override;
+    void notifyMasterParamSource() override;
     double getBpm() const override;
     void setInstantaneousBpm(double bpm) override;
     void setMasterParams(double beatDistance, double baseBpm, double bpm) override;
diff --git a/src/engine/sync/syncable.h b/src/engine/sync/syncable.h
index d25e54d0a09..19678be6229 100644
--- a/src/engine/sync/syncable.h
+++ b/src/engine/sync/syncable.h
@@ -112,6 +112,11 @@ class Syncable {
     // signal loops could occur.
     virtual void setMasterBpm(double bpm) = 0;
 
+    // Tells a Syncable that it's going to be used as a source for master
+    // params. This is a gross hack so that the SyncControl can undo its
+    // half/double adjustment.
+    virtual void notifyMasterParamSource() = 0;
+
     // Combines the above three calls into one, since they are often set
     // simultaneously.  Avoids redundant recalculation that would occur by
     // using the three calls separately.
diff --git a/src/engine/sync/synccontrol.cpp b/src/engine/sync/synccontrol.cpp
index 060cab53257..9c9a3c0b9d0 100644
--- a/src/engine/sync/synccontrol.cpp
+++ b/src/engine/sync/synccontrol.cpp
@@ -212,6 +212,7 @@ void SyncControl::setMasterBeatDistance(double beatDistance) {
     // Set the BpmControl target beat distance to beatDistance, adjusted by
     // the multiplier if in effect.  This way all of the multiplier logic
     // is contained in this single class.
+    m_lastTargetBeatDistance = m_unmultipliedTargetBeatDistance;
     m_unmultipliedTargetBeatDistance = beatDistance;
     // Update the target beat distance based on the multiplier.
     updateTargetBeatDistance();
@@ -238,19 +239,37 @@ void SyncControl::setMasterBpm(double bpm) {
     }
 }
 
+void SyncControl::notifyMasterParamSource() {
+    m_masterBpmAdjustFactor = kBpmUnity;
+}
+
 void SyncControl::setMasterParams(
         double beatDistance, double baseBpm, double bpm) {
+    qDebug() << "SyncControl::setMasterParams" << getGroup() << beatDistance << baseBpm << bpm;
+    // if (paramSource == this) {
+    //     baseBpm *= m_masterBpmAdjustFactor;
+    //     bpm *= m_masterBpmAdjustFactor;
+    //     qDebug() << "we were param source, undo adjust factor:" << baseBpm << bpm;
+    // }
     // Calculate the factor for the file bpm. That gives the best
     // result at any rate slider position.
-    double masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    if (isMaster(getSyncMode())) {
-        // In Master mode we adjust the incoming Bpm for the initial sync.
-        bpm *= masterBpmAdjustFactor;
-        m_masterBpmAdjustFactor = kBpmUnity;
-    } else {
-        // in Follower mode we keep the factor when reporting our BPM
-        m_masterBpmAdjustFactor = masterBpmAdjustFactor;
-    }
+    qDebug() << "file bpm: " << fileBpm();
+
+    // masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    // double masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    // if (paramSource == this) {
+    //     //     qDebug() << "We were param source!";
+    //     //     // If we are the param source, we need to undo the adjustment factor
+    //     //     // or else we start piling multipliers on top of each other.
+    //     //     bpm *= masterBpmAdjustFactor;
+    //     m_masterBpmAdjustFactor = kBpmUnity;
+    // } else {
+    //     m_masterBpmAdjustFactor = masterBpmAdjustFactor;
+    // }
+
+    // m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    qDebug() << "ADJUST FACTOR?!" << m_masterBpmAdjustFactor;
     setMasterBpm(bpm);
     setMasterBeatDistance(beatDistance);
 }
@@ -274,7 +293,10 @@ double SyncControl::determineBpmMultiplier(double myBpm, double targetBpm) const
 void SyncControl::updateTargetBeatDistance() {
     double targetDistance = m_unmultipliedTargetBeatDistance;
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "SyncControl::updateTargetBeatDistance, unmult distance" << targetDistance;
+        kLogger.trace()
+                << getGroup()
+                << "SyncControl::updateTargetBeatDistance, unmult distance"
+                << targetDistance << m_masterBpmAdjustFactor;
     }
 
     // Determining the target distance is not as simple as x2 or /2.  Since one
@@ -289,7 +311,9 @@ void SyncControl::updateTargetBeatDistance() {
         targetDistance *= kBpmDouble;
     } else if (m_masterBpmAdjustFactor == kBpmHalve) {
         targetDistance *= kBpmHalve;
-        if (m_pBeatDistance->get() >= 0.5) {
+        qDebug() << "my beat dist" << m_pBeatDistance->get();
+        // Our beat distance CO is still a buffer behind, so take the current value.
+        if (m_pBpmControl->getBeatDistance(getSampleOfTrack().current) >= 0.5) {
             targetDistance += 0.5;
         }
     }
@@ -301,7 +325,8 @@ void SyncControl::updateTargetBeatDistance() {
 
 double SyncControl::getBpm() const {
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "SyncControl::getBpm()";
+        kLogger.trace() << getGroup() << "SyncControl::getBpm()"
+                        << m_pBpm->get() << "/" << m_masterBpmAdjustFactor;
     }
     return m_pBpm->get() / m_masterBpmAdjustFactor;
 }
@@ -441,6 +466,7 @@ void SyncControl::setLocalBpm(double local_bpm) {
     if (local_bpm == m_prevLocalBpm.getValue()) {
         return;
     }
+    qDebug() << "SyncControl::setLocalBpm" << getGroup() << local_bpm;
     m_prevLocalBpm.setValue(local_bpm);
 
     SyncMode syncMode = getSyncMode();
diff --git a/src/engine/sync/synccontrol.h b/src/engine/sync/synccontrol.h
index ccdff1e4f54..32781b42ff3 100644
--- a/src/engine/sync/synccontrol.h
+++ b/src/engine/sync/synccontrol.h
@@ -48,10 +48,10 @@ class SyncControl : public EngineControl, public Syncable {
     // Must never result in a call to
     // SyncableListener::notifyBeatDistanceChanged or signal loops could occur.
     void setMasterBeatDistance(double beatDistance) override;
-
     // Must never result in a call to
     // SyncableListener::notifyBpmChanged or signal loops could occur.
     void setMasterBpm(double bpm) override;
+    void notifyMasterParamSource() override;
     void setMasterParams(double beatDistance, double baseBpm, double bpm) override;
 
     // Must never result in a call to
@@ -113,6 +113,7 @@ class SyncControl : public EngineControl, public Syncable {
     // It is handy to store the raw reported target beat distance in case the
     // multiplier changes and we need to recalculate the target distance.
     double m_unmultipliedTargetBeatDistance;
+    double m_lastTargetBeatDistance;
     ControlValueAtomic<double> m_prevLocalBpm;
     QAtomicInt m_audible;
 
diff --git a/src/test/enginesynctest.cpp b/src/test/enginesynctest.cpp
index 7d00c4a7e2e..39a216db188 100644
--- a/src/test/enginesynctest.cpp
+++ b/src/test/enginesynctest.cpp
@@ -1660,14 +1660,16 @@ TEST_F(EngineSyncTest, HalfDoubleBpmTest) {
             ->set(SYNC_FOLLOWER);
 
     // Mixxx will choose the first playing deck to be master.  Let's start deck 2 first.
+    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch2 play";
     ControlObject::getControl(ConfigKey(m_sGroup2, "play"))->set(1.0);
+    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch1 play";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
     ProcessBuffer();
 
-    EXPECT_EQ(1.0,
+    EXPECT_EQ(0.5,
             m_pChannel1->getEngineBuffer()
                     ->m_pSyncControl->m_masterBpmAdjustFactor);
-    EXPECT_EQ(2.0,
+    EXPECT_EQ(1.0,
             m_pChannel2->getEngineBuffer()
                     ->m_pSyncControl->m_masterBpmAdjustFactor);
     EXPECT_DOUBLE_EQ(
@@ -1789,7 +1791,7 @@ TEST_F(EngineSyncTest, HalfDoubleThenPlay) {
 
     ProcessBuffer();
 
-    EXPECT_DOUBLE_EQ(87.5,
+    EXPECT_DOUBLE_EQ(175,
             ControlObject::getControl(ConfigKey(m_sInternalClockGroup, "bpm"))
                     ->get());
 
@@ -1997,7 +1999,9 @@ TEST_F(EngineSyncTest, SyncPhaseToPlayingNonSyncDeck) {
     // Next Deck becomes master and the Master clock is set to 100 BPM
     // The 130 BPM Track should be played at 100 BPM, rate = 0.769230769
     pButtonSyncEnabled1->set(1.0);
+    qDebug() << "PUSH PLAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAY";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
+
     // Beat length: 40707.692307692305
     // Buffer size is 1024 at 44.1 kHz at the given rate = 787.692307692 Samples
     // Expected beat_distance = 0.019349962
@@ -2021,12 +2025,13 @@ TEST_F(EngineSyncTest, SyncPhaseToPlayingNonSyncDeck) {
 
     ProcessBuffer();
 
-    // we expect that Deck 1 distance has not changed and the internal clock follows it exactly.
+    // we expect that Deck 1 distance has not changed but the internal clock keeps going, because
+    // the internal clock should continue playing even if the leader is stopped.
     EXPECT_TRUE(isSoftMaster(m_sGroup1));
     EXPECT_NEAR(0.019349962,
             ControlObject::getControl(ConfigKey(m_sGroup1, "beat_distance"))->get(),
             kMaxFloatingPointErrorLowPrecision);
-    EXPECT_NEAR(0.019349962,
+    EXPECT_NEAR(0.038699924,
             ControlObject::getControl(ConfigKey(m_sInternalClockGroup, "beat_distance"))->get(),
             kMaxFloatingPointErrorLowPrecision);
 

From bd560c0610d2c3ab902466e88188085c96b9904c Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Sun, 23 May 2021 14:29:36 -0400
Subject: [PATCH 13/22] Sync Lock: Fix more half/double issues and clean up for
 PR

---
 src/engine/controls/bpmcontrol.cpp |  6 ++-
 src/engine/enginebuffer.cpp        |  1 -
 src/engine/enginemaster.cpp        |  8 ++-
 src/engine/sync/enginesync.cpp     | 83 +++++++++++-------------------
 src/engine/sync/enginesync.h       |  5 +-
 src/engine/sync/syncable.h         |  2 +-
 src/engine/sync/synccontrol.cpp    | 31 ++---------
 src/engine/sync/synccontrol.h      |  1 -
 src/test/enginesynctest.cpp        | 21 ++++++--
 9 files changed, 61 insertions(+), 97 deletions(-)

diff --git a/src/engine/controls/bpmcontrol.cpp b/src/engine/controls/bpmcontrol.cpp
index 3dae2ae609a..fac2e68e87d 100644
--- a/src/engine/controls/bpmcontrol.cpp
+++ b/src/engine/controls/bpmcontrol.cpp
@@ -536,7 +536,9 @@ double BpmControl::getBeatDistance(double dThisPosition) const {
     // we don't adjust the reported distance the track will try to adjust
     // sync against itself.
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "BpmControl::getBeatDistance" << dThisPosition;
+        kLogger.trace() << getGroup()
+                        << "BpmControl::getBeatDistance. dThisPosition:"
+                        << dThisPosition;
     }
     double dPrevBeat = m_pPrevBeat->get();
     double dNextBeat = m_pNextBeat->get();
@@ -560,7 +562,7 @@ double BpmControl::getBeatDistance(double dThisPosition) const {
     }
 
     if (kLogger.traceEnabled()) {
-        kLogger.trace() << getGroup() << "BpmControl::getBeatDistance"
+        kLogger.trace() << getGroup() << "BpmControl::getBeatDistance. dBeatPercentage:"
                         << dBeatPercentage << "-  offset "
                         << m_dUserOffset.getValue() << " =  "
                         << (dBeatPercentage - m_dUserOffset.getValue());
diff --git a/src/engine/enginebuffer.cpp b/src/engine/enginebuffer.cpp
index 4a5d011d40b..80065ba2b25 100644
--- a/src/engine/enginebuffer.cpp
+++ b/src/engine/enginebuffer.cpp
@@ -1297,7 +1297,6 @@ void EngineBuffer::postProcess(const int iBufferSize) {
     }
     double localBpm = m_pBpmControl->updateLocalBpm();
     double beatDistance = m_pBpmControl->updateBeatDistance();
-    qDebug() << getGroup() << "beat distance updated" << beatDistance;
     m_pSyncControl->setLocalBpm(localBpm);
     m_pSyncControl->updateAudible();
     SyncMode mode = m_pSyncControl->getSyncMode();
diff --git a/src/engine/enginemaster.cpp b/src/engine/enginemaster.cpp
index cda9a1dbb51..202fe0b1341 100644
--- a/src/engine/enginemaster.cpp
+++ b/src/engine/enginemaster.cpp
@@ -369,11 +369,9 @@ void EngineMaster::processChannels(int iBufferSize) {
 
     // Do internal master sync post-processing before the other
     // channels.
-    // OK, so this means the internal clock knows that it has crossed a beat
-    // boundary before the channels do. This means when we call this, we
-    // notify all the channels that the master beat distance has changed.
-    // They try to update the target beat distance, and guess the
-    // wrong number because they can't do half/double calculation correctly.
+    // Note, because we call this on the internal clock first,
+    // it will have an up-to-date beatDistance, whereas the other
+    // Syncables will not.
     m_pMasterSync->onCallbackEnd(m_iSampleRate, m_iBufferSize);
 
     // After all the engines have been processed, trigger post-processing
diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index f913eb8c73d..fad3c6ed696 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -96,15 +96,8 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    auto players = getPlayingSyncables();
-    if (players.size() == 1) {
-        qDebug() << "!!!!!!!!!!!!!!!!!!!!!1there is only one playing syncable, tell it so!";
-        players.at(0)->notifyOnlyPlayingSyncable();
-    } else {
-        qDebug() << "players!";
-        for (auto* play : players) {
-            qDebug() << play->getGroup();
-        }
+    if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
+        onlyPlayer->notifyOnlyPlayingSyncable();
     }
 }
 
@@ -358,30 +351,11 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
     if (newMaster != nullptr && newMaster != m_pMasterSyncable) {
         activateMaster(newMaster, SYNC_MASTER_SOFT);
         setMasterParams(newMaster);
-    }
-
-    // we know for a fact that pSyncable is playing and audible.
-    // We want to init master params
-    // cases:
-    // just we are playing: set master params with our settings
-    // NO. just because we are master, doesn't mean we win! we might be copying someone else.
-    // if anything we should JUST init beat distance.
-    // another deck is playing and it's master: don't touch it
-    // another deck is playing and it's not master: don't touch it
-    auto players = getPlayingSyncables();
-    if (players.size() == 1) {
-        Syncable* onlyPlayer = players.at(0);
-        qDebug() << "2222222222222222222222222222 there is only one playing "
-                    "syncable, it gets to set beat dist"
-                 << onlyPlayer->getGroup();
+    } else if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
+        // Even if we didn't change master, if there is only one player (us), then we should
+        // reinit the beat distance.
         onlyPlayer->notifyOnlyPlayingSyncable();
-        // setMasterParams(onlyPlayer);
         setMasterBeatDistance(onlyPlayer, onlyPlayer->getBeatDistance());
-    } else {
-        qDebug() << "players!";
-        for (auto* play : players) {
-            qDebug() << play->getGroup();
-        }
     }
 
     pSyncable->requestSync();
@@ -611,6 +585,11 @@ void EngineSync::setMasterInstantaneousBpm(Syncable* pSource, double bpm) {
 }
 
 void EngineSync::setMasterBeatDistance(Syncable* pSource, double beatDistance) {
+    if (kLogger.traceEnabled()) {
+        kLogger.trace() << "EngineSync::setMasterBeatDistance"
+                        << (pSource ? pSource->getGroup() : "null")
+                        << beatDistance;
+    }
     if (pSource != m_pInternalClock) {
         m_pInternalClock->setMasterBeatDistance(beatDistance);
     }
@@ -624,55 +603,47 @@ void EngineSync::setMasterBeatDistance(Syncable* pSource, double beatDistance) {
 }
 
 void EngineSync::setMasterParams(Syncable* pSource) {
-    // so the bug here is that we are setting the master parameters from some source, but
-    // that source may not be the master! but when we update the multipliers, we update
-    // based on who is master. We used to try to force master to be multiplier 1.0, but that
-    // causes problems.
-
+    // Important note! Because of the way sync works, the new master is usually not the same
+    // as the Syncable setting the master parameters (here, pSource). Notify the proper Syncable
+    // so it can prepare itself.  (This is a hack to undo half/double math so that we initialize
+    // based on un-multiplied bpm values).
     pSource->notifyMasterParamSource();
 
     double beatDistance = pSource->getBeatDistance();
-    // // If the params source is not playing, but other syncables are, then we are a stopped
-    // // explicit Master and we should not initialize the beat distance.  Take it from the
-    // // internal clock instead.
     if (!pSource->isPlaying()) {
+        // If the params source is not playing, but other syncables are, then we are a stopped
+        // explicit Master and we should not initialize the beat distance.  Take it from the
+        // internal clock instead.
         bool playingSyncables = false;
         for (Syncable* pSyncable : m_syncables) {
-            qDebug() << "checking" << pSyncable->getGroup();
             if (pSyncable == pSource) {
                 continue;
             }
             if (!pSyncable->isSynchronized()) {
                 continue;
             }
-            qDebug() << "it's valid";
             if (pSyncable->isPlaying()) {
-                qDebug() << "found a playing syncable" << pSyncable->getGroup();
                 playingSyncables = true;
                 break;
             }
         }
         if (playingSyncables) {
-            qDebug() << "~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"
-                        "BaseSyncableListener::setMasterParams, not playing, "
-                        "playing followers, pull from internal clock"
-                     << pSource->getGroup();
             beatDistance = m_pInternalClock->getBeatDistance();
         }
     }
-    // Do we want the RAW values here, not multiplied by adjust factor??
     const double baseBpm = pSource->getBaseBpm();
     double bpm = pSource->getBpm();
     if (bpm <= 0) {
         bpm = baseBpm;
     }
-    qDebug() << "BaseSyncableListener::setMasterParams, source is"
-             << pSource->getGroup() << beatDistance << baseBpm << bpm;
+    if (kLogger.traceEnabled()) {
+        kLogger.trace() << "BaseSyncableListener::setMasterParams, source is"
+                        << pSource->getGroup() << beatDistance << baseBpm << bpm;
+    }
     if (pSource != m_pInternalClock) {
         m_pInternalClock->setMasterParams(beatDistance, baseBpm, bpm);
     }
     foreach (Syncable* pSyncable, m_syncables) {
-        // not sure if we should skip the pSource here.
         if (!pSyncable->isSynchronized()) {
             continue;
         }
@@ -680,16 +651,20 @@ void EngineSync::setMasterParams(Syncable* pSource) {
     }
 }
 
-QList<Syncable*> EngineSync::getPlayingSyncables() const {
-    QList<Syncable*> players;
+Syncable* EngineSync::getOnlyPlayingSyncable() const {
+    Syncable* onlyPlaying = nullptr;
     for (Syncable* pSyncable : m_syncables) {
         if (!pSyncable->isSynchronized()) {
             continue;
         }
 
         if (pSyncable->isPlaying()) {
-            players.append(pSyncable);
+            if (!onlyPlaying) {
+                onlyPlaying = pSyncable;
+            } else {
+                return nullptr;
+            }
         }
     }
-    return players;
+    return onlyPlaying;
 }
diff --git a/src/engine/sync/enginesync.h b/src/engine/sync/enginesync.h
index 8e306e14a91..4988a14c422 100644
--- a/src/engine/sync/enginesync.h
+++ b/src/engine/sync/enginesync.h
@@ -115,8 +115,9 @@ class EngineSync : public SyncableListener {
 
     void setMasterParams(Syncable* pSource);
 
-    /// Return the playing syncables, if any. This is used to initialize beat distance settings.
-    QList<Syncable*> getPlayingSyncables() const;
+    /// Iff there is a single playing syncable, return it. This is used to initialize master
+    /// params.
+    Syncable* getOnlyPlayingSyncable() const;
 
     /// Only for testing. Do not use.
     Syncable* getSyncableForGroup(const QString& group);
diff --git a/src/engine/sync/syncable.h b/src/engine/sync/syncable.h
index 19678be6229..fa29b1da915 100644
--- a/src/engine/sync/syncable.h
+++ b/src/engine/sync/syncable.h
@@ -114,7 +114,7 @@ class Syncable {
 
     // Tells a Syncable that it's going to be used as a source for master
     // params. This is a gross hack so that the SyncControl can undo its
-    // half/double adjustment.
+    // half/double adjustment so bpms are initialized correctly.
     virtual void notifyMasterParamSource() = 0;
 
     // Combines the above three calls into one, since they are often set
diff --git a/src/engine/sync/synccontrol.cpp b/src/engine/sync/synccontrol.cpp
index 9c9a3c0b9d0..d387a22488c 100644
--- a/src/engine/sync/synccontrol.cpp
+++ b/src/engine/sync/synccontrol.cpp
@@ -212,7 +212,6 @@ void SyncControl::setMasterBeatDistance(double beatDistance) {
     // Set the BpmControl target beat distance to beatDistance, adjusted by
     // the multiplier if in effect.  This way all of the multiplier logic
     // is contained in this single class.
-    m_lastTargetBeatDistance = m_unmultipliedTargetBeatDistance;
     m_unmultipliedTargetBeatDistance = beatDistance;
     // Update the target beat distance based on the multiplier.
     updateTargetBeatDistance();
@@ -245,31 +244,11 @@ void SyncControl::notifyMasterParamSource() {
 
 void SyncControl::setMasterParams(
         double beatDistance, double baseBpm, double bpm) {
-    qDebug() << "SyncControl::setMasterParams" << getGroup() << beatDistance << baseBpm << bpm;
-    // if (paramSource == this) {
-    //     baseBpm *= m_masterBpmAdjustFactor;
-    //     bpm *= m_masterBpmAdjustFactor;
-    //     qDebug() << "we were param source, undo adjust factor:" << baseBpm << bpm;
-    // }
-    // Calculate the factor for the file bpm. That gives the best
-    // result at any rate slider position.
-    qDebug() << "file bpm: " << fileBpm();
-
-    // masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    // double masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
+    if (kLogger.traceEnabled()) {
+        kLogger.trace() << "SyncControl::setMasterParams" << getGroup()
+                        << beatDistance << baseBpm << bpm;
+    }
     m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    // if (paramSource == this) {
-    //     //     qDebug() << "We were param source!";
-    //     //     // If we are the param source, we need to undo the adjustment factor
-    //     //     // or else we start piling multipliers on top of each other.
-    //     //     bpm *= masterBpmAdjustFactor;
-    //     m_masterBpmAdjustFactor = kBpmUnity;
-    // } else {
-    //     m_masterBpmAdjustFactor = masterBpmAdjustFactor;
-    // }
-
-    // m_masterBpmAdjustFactor = determineBpmMultiplier(fileBpm(), baseBpm);
-    qDebug() << "ADJUST FACTOR?!" << m_masterBpmAdjustFactor;
     setMasterBpm(bpm);
     setMasterBeatDistance(beatDistance);
 }
@@ -311,7 +290,6 @@ void SyncControl::updateTargetBeatDistance() {
         targetDistance *= kBpmDouble;
     } else if (m_masterBpmAdjustFactor == kBpmHalve) {
         targetDistance *= kBpmHalve;
-        qDebug() << "my beat dist" << m_pBeatDistance->get();
         // Our beat distance CO is still a buffer behind, so take the current value.
         if (m_pBpmControl->getBeatDistance(getSampleOfTrack().current) >= 0.5) {
             targetDistance += 0.5;
@@ -466,7 +444,6 @@ void SyncControl::setLocalBpm(double local_bpm) {
     if (local_bpm == m_prevLocalBpm.getValue()) {
         return;
     }
-    qDebug() << "SyncControl::setLocalBpm" << getGroup() << local_bpm;
     m_prevLocalBpm.setValue(local_bpm);
 
     SyncMode syncMode = getSyncMode();
diff --git a/src/engine/sync/synccontrol.h b/src/engine/sync/synccontrol.h
index 32781b42ff3..357106fca94 100644
--- a/src/engine/sync/synccontrol.h
+++ b/src/engine/sync/synccontrol.h
@@ -113,7 +113,6 @@ class SyncControl : public EngineControl, public Syncable {
     // It is handy to store the raw reported target beat distance in case the
     // multiplier changes and we need to recalculate the target distance.
     double m_unmultipliedTargetBeatDistance;
-    double m_lastTargetBeatDistance;
     ControlValueAtomic<double> m_prevLocalBpm;
     QAtomicInt m_audible;
 
diff --git a/src/test/enginesynctest.cpp b/src/test/enginesynctest.cpp
index 39a216db188..66351320754 100644
--- a/src/test/enginesynctest.cpp
+++ b/src/test/enginesynctest.cpp
@@ -1445,6 +1445,23 @@ TEST_F(EngineSyncTest, ZeroBPMRateAdjustIgnored) {
             ControlObject::getControl(ConfigKey(m_sGroup2, "rate"))->get());
 }
 
+TEST_F(EngineSyncTest, DISABLED_BeatDistanceBeforeStart) {
+    // If the start position is before zero, we should still initialize the beat distance
+    // corretly.  Unfortunately, this currently doesn't work.
+
+    mixxx::BeatsPointer pBeats1 = BeatFactory::makeBeatGrid(m_pTrack1->getSampleRate(), 128, 0.0);
+    m_pTrack1->trySetBeats(pBeats1);
+    ControlObject::set(ConfigKey(m_sGroup1, "playposition"), -.05);
+    ControlObject::getControl(ConfigKey(m_sGroup1, "sync_mode"))
+            ->set(SYNC_MASTER_SOFT);
+    ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
+    ProcessBuffer();
+    EXPECT_NEAR(
+            ControlObject::getControl(ConfigKey(m_sGroup1, "beat_distance"))->get(),
+            ControlObject::getControl(ConfigKey(m_sInternalClockGroup, "beat_distance"))->get(),
+            kMaxBeatDistanceEpsilon);
+}
+
 TEST_F(EngineSyncTest, ZeroLatencyRateChangeNoQuant) {
     // Confirm that a rate change in an explicit master is instantly communicated
     // to followers.
@@ -1660,9 +1677,7 @@ TEST_F(EngineSyncTest, HalfDoubleBpmTest) {
             ->set(SYNC_FOLLOWER);
 
     // Mixxx will choose the first playing deck to be master.  Let's start deck 2 first.
-    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch2 play";
     ControlObject::getControl(ConfigKey(m_sGroup2, "play"))->set(1.0);
-    qDebug() << "~~~~~~~~~~~~~~~~~~~~ ch1 play";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
     ProcessBuffer();
 
@@ -1999,9 +2014,7 @@ TEST_F(EngineSyncTest, SyncPhaseToPlayingNonSyncDeck) {
     // Next Deck becomes master and the Master clock is set to 100 BPM
     // The 130 BPM Track should be played at 100 BPM, rate = 0.769230769
     pButtonSyncEnabled1->set(1.0);
-    qDebug() << "PUSH PLAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAY";
     ControlObject::getControl(ConfigKey(m_sGroup1, "play"))->set(1.0);
-
     // Beat length: 40707.692307692305
     // Buffer size is 1024 at 44.1 kHz at the given rate = 787.692307692 Samples
     // Expected beat_distance = 0.019349962

From 4e9f8f4ee4060b5ade8dc587be92f390ae7fd35d Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Fri, 28 May 2021 18:53:48 -0400
Subject: [PATCH 14/22] Sync Lock: Fix clazy issue

---
 src/engine/sync/enginesync.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index fad3c6ed696..1b8e876e010 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -615,7 +615,7 @@ void EngineSync::setMasterParams(Syncable* pSource) {
         // explicit Master and we should not initialize the beat distance.  Take it from the
         // internal clock instead.
         bool playingSyncables = false;
-        for (Syncable* pSyncable : m_syncables) {
+        for (Syncable* pSyncable : qAsConst(m_syncables)) {
             if (pSyncable == pSource) {
                 continue;
             }

From 4ccdebe0390b47bee6bf3e789a5e9882d94dd202 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Sat, 29 May 2021 13:35:39 -0400
Subject: [PATCH 15/22] sync lock: add bug link for disabled / broken test

---
 src/test/enginesynctest.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/test/enginesynctest.cpp b/src/test/enginesynctest.cpp
index 66351320754..953c9405e62 100644
--- a/src/test/enginesynctest.cpp
+++ b/src/test/enginesynctest.cpp
@@ -1446,8 +1446,9 @@ TEST_F(EngineSyncTest, ZeroBPMRateAdjustIgnored) {
 }
 
 TEST_F(EngineSyncTest, DISABLED_BeatDistanceBeforeStart) {
+    // https://bugs.launchpad.net/mixxx/+bug/1930143
     // If the start position is before zero, we should still initialize the beat distance
-    // corretly.  Unfortunately, this currently doesn't work.
+    // correctly.  Unfortunately, this currently doesn't work.
 
     mixxx::BeatsPointer pBeats1 = BeatFactory::makeBeatGrid(m_pTrack1->getSampleRate(), 128, 0.0);
     m_pTrack1->trySetBeats(pBeats1);

From 259cfa506fca605d045a08b198c36600ba2b5b1f Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Mon, 31 May 2021 22:58:19 -0400
Subject: [PATCH 16/22] Sync Lock: don't use c++17 inline conditional
 assignment (1)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Daniel Schürmann <daschuer@mixxx.org>
---
 src/engine/sync/enginesync.cpp | 22 +++++++++++++---------
 src/engine/sync/enginesync.h   |  6 +++---
 2 files changed, 16 insertions(+), 12 deletions(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 1b8e876e010..f187d8b20bd 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -96,8 +96,9 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
-        onlyPlayer->notifyOnlyPlayingSyncable();
+    Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
+    if (pOnlyPlayer) {
+        pOnlyPlayer->notifyOnlyPlayingSyncable();
     }
 }
 
@@ -351,11 +352,14 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
     if (newMaster != nullptr && newMaster != m_pMasterSyncable) {
         activateMaster(newMaster, SYNC_MASTER_SOFT);
         setMasterParams(newMaster);
-    } else if (auto onlyPlayer = getOnlyPlayingSyncable(); onlyPlayer != nullptr) {
-        // Even if we didn't change master, if there is only one player (us), then we should
-        // reinit the beat distance.
-        onlyPlayer->notifyOnlyPlayingSyncable();
-        setMasterBeatDistance(onlyPlayer, onlyPlayer->getBeatDistance());
+    } else {
+        Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
+        if (pOnlyPlayer) {
+            // Even if we didn't change master, if there is only one player (us), then we should
+            // reinit the beat distance.
+            pOnlyPlayer->notifyOnlyPlayingSyncable();
+            setMasterBeatDistance(pOnlyPlayer, pOnlyPlayer->getBeatDistance());
+        }
     }
 
     pSyncable->requestSync();
@@ -613,7 +617,7 @@ void EngineSync::setMasterParams(Syncable* pSource) {
     if (!pSource->isPlaying()) {
         // If the params source is not playing, but other syncables are, then we are a stopped
         // explicit Master and we should not initialize the beat distance.  Take it from the
-        // internal clock instead.
+        // internal clock instead, because that will be up to date with the playing deck(s).
         bool playingSyncables = false;
         for (Syncable* pSyncable : qAsConst(m_syncables)) {
             if (pSyncable == pSource) {
@@ -651,7 +655,7 @@ void EngineSync::setMasterParams(Syncable* pSource) {
     }
 }
 
-Syncable* EngineSync::getOnlyPlayingSyncable() const {
+Syncable* EngineSync::getUniquePlayingSyncedDeck() const {
     Syncable* onlyPlaying = nullptr;
     for (Syncable* pSyncable : m_syncables) {
         if (!pSyncable->isSynchronized()) {
diff --git a/src/engine/sync/enginesync.h b/src/engine/sync/enginesync.h
index 4988a14c422..5ce7574b520 100644
--- a/src/engine/sync/enginesync.h
+++ b/src/engine/sync/enginesync.h
@@ -115,9 +115,9 @@ class EngineSync : public SyncableListener {
 
     void setMasterParams(Syncable* pSource);
 
-    /// Iff there is a single playing syncable, return it. This is used to initialize master
-    /// params.
-    Syncable* getOnlyPlayingSyncable() const;
+    /// Iff there is a single playing syncable in sync mode, return it.
+    /// This is used to initialize master params.
+    Syncable* getUniquePlayingSyncedDeck() const;
 
     /// Only for testing. Do not use.
     Syncable* getSyncableForGroup(const QString& group);

From d450bca683f82bfe5bd6b6e9482fa566e1cf7a62 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Mon, 31 May 2021 23:32:29 -0400
Subject: [PATCH 17/22] Sync Lock: Fix issue where single playing sync deck was
 syncing against its nudge value

---
 src/engine/sync/enginesync.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index f187d8b20bd..2e7a5bec784 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -75,6 +75,13 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
     default:;
     }
 
+    Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
+    if (pOnlyPlayer) {
+        // This resets the user offset, so that if this deck gets used as the params syncable
+        // it will have that offset removed.
+        pOnlyPlayer->notifyOnlyPlayingSyncable();
+    }
+
     // Second, figure out what Syncable should be used to initialize the master
     // parameters, if any. Usually this is the new master. (Note, that pointer might be null!)
     Syncable* pParamsSyncable = m_pMasterSyncable;
@@ -96,10 +103,6 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
         }
     }
 
-    Syncable* pOnlyPlayer = getUniquePlayingSyncedDeck();
-    if (pOnlyPlayer) {
-        pOnlyPlayer->notifyOnlyPlayingSyncable();
-    }
 }
 
 void EngineSync::activateFollower(Syncable* pSyncable) {

From b0c51f05139d2900fc2b135dfe18cfba9ddc65f5 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 14:20:25 -0400
Subject: [PATCH 18/22] Sync Lock: better name for function

---
 src/engine/sync/enginesync.cpp    | 4 ++--
 src/engine/sync/internalclock.cpp | 2 +-
 src/engine/sync/internalclock.h   | 2 +-
 src/engine/sync/syncable.h        | 2 +-
 src/engine/sync/synccontrol.cpp   | 2 +-
 src/engine/sync/synccontrol.h     | 2 +-
 6 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/engine/sync/enginesync.cpp b/src/engine/sync/enginesync.cpp
index 2e7a5bec784..474ff418e99 100644
--- a/src/engine/sync/enginesync.cpp
+++ b/src/engine/sync/enginesync.cpp
@@ -79,7 +79,7 @@ void EngineSync::requestSyncMode(Syncable* pSyncable, SyncMode mode) {
     if (pOnlyPlayer) {
         // This resets the user offset, so that if this deck gets used as the params syncable
         // it will have that offset removed.
-        pOnlyPlayer->notifyOnlyPlayingSyncable();
+        pOnlyPlayer->notifyUniquePlaying();
     }
 
     // Second, figure out what Syncable should be used to initialize the master
@@ -360,7 +360,7 @@ void EngineSync::notifyPlayingAudible(Syncable* pSyncable, bool playingAudible)
         if (pOnlyPlayer) {
             // Even if we didn't change master, if there is only one player (us), then we should
             // reinit the beat distance.
-            pOnlyPlayer->notifyOnlyPlayingSyncable();
+            pOnlyPlayer->notifyUniquePlaying();
             setMasterBeatDistance(pOnlyPlayer, pOnlyPlayer->getBeatDistance());
         }
     }
diff --git a/src/engine/sync/internalclock.cpp b/src/engine/sync/internalclock.cpp
index 8c3731f2397..734523d7e83 100644
--- a/src/engine/sync/internalclock.cpp
+++ b/src/engine/sync/internalclock.cpp
@@ -60,7 +60,7 @@ void InternalClock::setSyncMode(SyncMode mode) {
     m_pSyncMasterEnabled->setAndConfirm(SyncModeToMasterLight(mode));
 }
 
-void InternalClock::notifyOnlyPlayingSyncable() {
+void InternalClock::notifyUniquePlaying() {
     // No action necessary.
 }
 
diff --git a/src/engine/sync/internalclock.h b/src/engine/sync/internalclock.h
index dea03a490d7..da0ddde7509 100644
--- a/src/engine/sync/internalclock.h
+++ b/src/engine/sync/internalclock.h
@@ -32,7 +32,7 @@ class InternalClock : public QObject, public Clock, public Syncable {
     }
 
     void setSyncMode(SyncMode mode) override;
-    void notifyOnlyPlayingSyncable() override;
+    void notifyUniquePlaying() override;
     void requestSync() override;
     SyncMode getSyncMode() const override {
         return m_mode;
diff --git a/src/engine/sync/syncable.h b/src/engine/sync/syncable.h
index fa29b1da915..1596b378cbb 100644
--- a/src/engine/sync/syncable.h
+++ b/src/engine/sync/syncable.h
@@ -76,7 +76,7 @@ class Syncable {
     virtual void setSyncMode(SyncMode mode) = 0;
 
     // Notify a Syncable that it is now the only currently-playing syncable.
-    virtual void notifyOnlyPlayingSyncable() = 0;
+    virtual void notifyUniquePlaying() = 0;
 
     // Notify a Syncable that they should sync phase.
     virtual void requestSync() = 0;
diff --git a/src/engine/sync/synccontrol.cpp b/src/engine/sync/synccontrol.cpp
index d387a22488c..728a51d9b39 100644
--- a/src/engine/sync/synccontrol.cpp
+++ b/src/engine/sync/synccontrol.cpp
@@ -145,7 +145,7 @@ void SyncControl::setSyncMode(SyncMode mode) {
     }
 }
 
-void SyncControl::notifyOnlyPlayingSyncable() {
+void SyncControl::notifyUniquePlaying() {
     // If we are the only remaining playing sync deck, we can reset the user
     // tweak info.
     m_pBpmControl->resetSyncAdjustment();
diff --git a/src/engine/sync/synccontrol.h b/src/engine/sync/synccontrol.h
index 357106fca94..69af12e6c65 100644
--- a/src/engine/sync/synccontrol.h
+++ b/src/engine/sync/synccontrol.h
@@ -30,7 +30,7 @@ class SyncControl : public EngineControl, public Syncable {
 
     SyncMode getSyncMode() const override;
     void setSyncMode(SyncMode mode) override;
-    void notifyOnlyPlayingSyncable() override;
+    void notifyUniquePlaying() override;
     void requestSync() override;
     bool isPlaying() const override;
     bool isAudible() const override;

From 372d9e43b1844feea7950e76bcb1f5f4de46709f Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 15:05:54 -0400
Subject: [PATCH 19/22] SyncLock: Increase deck size to make room for Leader
 button

---
 res/skins/LateNight/decks/deck.xml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/res/skins/LateNight/decks/deck.xml b/res/skins/LateNight/decks/deck.xml
index 9c42c500528..7f6d1228641 100644
--- a/res/skins/LateNight/decks/deck.xml
+++ b/res/skins/LateNight/decks/deck.xml
@@ -2,7 +2,7 @@
 
   <WidgetGroup>
     <Layout>vertical</Layout>
-    <MaximumSize>,208</MaximumSize>
+    <MaximumSize>,230</MaximumSize>
     <Children>
 
       <Template src="skin:/decks/deck_singletons.xml">

From 08cead78906aa1291ec0e94783a0c4e47441634f Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 15:06:54 -0400
Subject: [PATCH 20/22] SyncLock: Fix leader button in latenight classic

---
 res/skins/LateNight/style_classic.qss | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/res/skins/LateNight/style_classic.qss b/res/skins/LateNight/style_classic.qss
index 17b4245e85a..ea4a6d214e0 100644
--- a/res/skins/LateNight/style_classic.qss
+++ b/res/skins/LateNight/style_classic.qss
@@ -1662,7 +1662,7 @@ WPushButton#SamplerExpand[displayValue="0"],
   }
 
 #SyncLeader {
-  background: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
+  image: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
   }
 
   #SyncSampler {

From 7efe9169840943309e29e305b443200a9c00a5c4 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 16:52:41 -0400
Subject: [PATCH 21/22] SyncLock: Skin fixes

---
 .../palemoon/buttons/btn__leader_deck.svg     | 87 +++++++++++++++++++
 res/skins/LateNight/style_classic.qss         |  2 +-
 res/skins/LateNight/style_palemoon.qss        |  8 +-
 3 files changed, 95 insertions(+), 2 deletions(-)
 create mode 100644 res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg

diff --git a/res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg b/res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg
new file mode 100644
index 00000000000..7f7de5bf879
--- /dev/null
+++ b/res/skins/LateNight/palemoon/buttons/btn__leader_deck.svg
@@ -0,0 +1,87 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   width="46"
+   height="20"
+   version="1.1"
+   id="svg32"
+   sodipodi:docname="btn__leader_deck.svg"
+   inkscape:version="0.92.5 (2060ec1f9f, 2020-04-08)">
+  <metadata
+     id="metadata38">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <defs
+     id="defs36" />
+  <sodipodi:namedview
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1"
+     objecttolerance="10"
+     gridtolerance="10"
+     guidetolerance="10"
+     inkscape:pageopacity="0"
+     inkscape:pageshadow="2"
+     inkscape:window-width="1920"
+     inkscape:window-height="1017"
+     id="namedview34"
+     showgrid="true"
+     inkscape:zoom="16"
+     inkscape:cx="23.740955"
+     inkscape:cy="16.667631"
+     inkscape:window-x="0"
+     inkscape:window-y="26"
+     inkscape:window-maximized="1"
+     inkscape:current-layer="svg32">
+    <inkscape:grid
+       type="xygrid"
+       id="grid854" />
+  </sodipodi:namedview>
+  <g
+     id="g10"
+     style="display:inline;fill:none"
+     transform="translate(-2,-2)">
+    <path
+       d="M 16,8 H 9 v 4 h 5 v 2 H 9 v 1 h 7 V 11 H 11 V 9 h 5 V 8"
+       id="path2"
+       inkscape:connector-curvature="0" />
+    <path
+       d="m 26,8 v 7 h 2 V 9 h 3 v 6 h 2 V 8 h -7"
+       id="path4"
+       inkscape:connector-curvature="0" />
+    <path
+       d="m 34,8 v 7 h 7 V 14 H 36 V 9 h 5 V 8 h -7"
+       id="path6"
+       inkscape:connector-curvature="0" />
+    <path
+       d="m 20,15 v -3.5 l -3,-3 V 8 h 1.5 L 21,10.5 23.5,8 H 25 v 0.5 l -3,3 V 15 h -2"
+       id="path8"
+       inkscape:connector-curvature="0" />
+  </g>
+  <text
+     xml:space="preserve"
+     style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:11.27830696px;line-height:0%;font-family:'Latina Essential';-inkscape-font-specification:'Latina Essential';writing-mode:lr-tb;opacity:1;fill:#d2d2d1;fill-opacity:1;stroke:#000000;stroke-width:0.84600008;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1"
+     x="0.056735612"
+     y="14.086957"
+     id="text4532"
+     transform="scale(1.0060601,0.99397642)"><tspan
+       sodipodi:role="line"
+       id="tspan4530"
+       x="0.056735612"
+       y="14.086957"
+       style="stroke-width:0.84600008">LEADER</tspan></text>
+</svg>
diff --git a/res/skins/LateNight/style_classic.qss b/res/skins/LateNight/style_classic.qss
index ea4a6d214e0..20c25f1844b 100644
--- a/res/skins/LateNight/style_classic.qss
+++ b/res/skins/LateNight/style_classic.qss
@@ -1314,7 +1314,7 @@ WPushButton#PlayIndicator,
 WPushButton#CueDeck,
 #PlayCueMini WPushButton,
 WPushButton#LoopActivate,
-#RateControls WPushButton,
+WPushButton#RateControls WPushButton,
 WPushButton#SyncDeck,
 WPushButton#SyncLeader,
 WPushButton#SyncSampler,
diff --git a/res/skins/LateNight/style_palemoon.qss b/res/skins/LateNight/style_palemoon.qss
index 4df0ee6c349..5063fc8b428 100644
--- a/res/skins/LateNight/style_palemoon.qss
+++ b/res/skins/LateNight/style_palemoon.qss
@@ -1522,7 +1522,9 @@ WPushButton#CueDeck,
 #PlayCueMini WPushButton,
 WPushButton#LoopActivate,
 WPushButton#RateControls WPushButton,
-WPushButton#SyncDeck, WPushButton#SyncSampler,
+WPushButton#SyncDeck,
+WPushButton#SyncLeader,
+WPushButton#SyncSampler,
 #MixerContainer WPushButton,
 #FxUnitContainer WPushButton,
 #Sampler WPushButton,
@@ -2105,6 +2107,10 @@ WPushButton#PlayDeck[value="0"] {
     image: url(skin:/palemoon/buttons/btn__sync_deck_active.svg) no-repeat center center;
   }
 
+#SyncLeader {
+  image: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
+  }
+
   #SyncSampler {
     image: url(skin:/palemoon/buttons/btn__sync_sampler.svg) no-repeat center center;
     }

From fc5813f270b308037cfd46c522a3845daf9ca4a6 Mon Sep 17 00:00:00 2001
From: Owen Williams <owilliams@mixxx.org>
Date: Thu, 3 Jun 2021 23:50:51 -0400
Subject: [PATCH 22/22] Sync Lock: Fix Leader button colors

---
 res/skins/LateNight/style_classic.qss  | 9 ++++++++-
 res/skins/LateNight/style_palemoon.qss | 6 ++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/res/skins/LateNight/style_classic.qss b/res/skins/LateNight/style_classic.qss
index 20c25f1844b..47dfad05a57 100644
--- a/res/skins/LateNight/style_classic.qss
+++ b/res/skins/LateNight/style_classic.qss
@@ -1378,10 +1378,17 @@ WPushButton#SkinSettingsToggle[displayValue="0"] {
   background-color: #262626;
 }
 
+/* Orange for 'partially active' status */
+#SyncLeader[value="1"] {
+background-color: #db7700;
+}
+
 /* Red for 'active' status */
 #BeatgridControls WPushButton[value="1"],
 #RateControls WPushButton[value="1"],
-#SyncDeck[value="1"], #SyncSampler[displayValue="1"],
+#SyncDeck[value="1"],
+#SyncLeader[value="2"],
+#SyncSampler[displayValue="1"],
 WPushButton#PlayDeck[displayValue="1"],
 WPushButton#PlayDeckMini[displayValue="1"],
 WPushButton#PlaySampler[displayValue="1"],
diff --git a/res/skins/LateNight/style_palemoon.qss b/res/skins/LateNight/style_palemoon.qss
index 5063fc8b428..0866164d5c6 100644
--- a/res/skins/LateNight/style_palemoon.qss
+++ b/res/skins/LateNight/style_palemoon.qss
@@ -1635,6 +1635,8 @@ WPushButton#Reverse[pressed="true"],
 #LoopActivate[value="1"],
 #Reloop[value="1"],
 #SyncSampler[displayValue="1"],
+#SyncDeck[value="1"],
+#SyncLeader[value="2"],
 #MicTalk[value="1"], #AuxPlay[value="1"],
 #MicDucking[value="1"],
 #MicDucking[value="2"],
@@ -1653,7 +1655,7 @@ QPushButton#pushButtonAnalyze:checked {
   }
 /* dim orange for momentary controls */
 #KeyControls WPushButton[pressed="true"],
-#SyncDeck[value="1"],
+#SyncLeader[value="1"],
 WPushButton#LoopIn[pressed="true"],
 WPushButton#LoopOut[pressed="true"],
 #BeatjumpControls WPushButton[value="1"],
@@ -2108,7 +2110,7 @@ WPushButton#PlayDeck[value="0"] {
   }
 
 #SyncLeader {
-  image: url(skin:/classic/buttons/btn__leader_deck.svg) no-repeat center center;
+  image: url(skin:/palemoon/buttons/btn__leader_deck.svg) no-repeat center center;
   }
 
   #SyncSampler {