Expose [BPM],sync_lock_algorithm option in deck preferences.

src/defs_urls.h

@@ -53,6 +53,8 @@
     MIXXX_MANUAL_URL "/chapters/preferences.html#library"
 #define MIXXX_MANUAL_CUE_MODES_URL \
     MIXXX_MANUAL_URL "/chapters/user_interface.html#using-cue-modes"
+#define MIXXX_MANUAL_SYNC_MODES_URL \
+    MIXXX_MANUAL_URL "/chapters/djing_with_mixxx#sync-lock-with-dynamic-tempo"
 #define MIXXX_MANUAL_BEATS_URL \
     MIXXX_MANUAL_URL "/chapters/preferences.html#beat-detection"
 #define MIXXX_MANUAL_KEY_URL \

src/engine/sync/enginesync.cpp

@@ -275,10 +275,10 @@ Syncable* EngineSync::pickNewLeader(Syncable* pEnablingSyncable) {
     }
 
     const SyncLockAlgorithm picker = static_cast<SyncLockAlgorithm>(
-            m_pConfig->getValue<int>(ConfigKey("[BPM]", "sync_lock_algorithm"),
-                    PREFER_IMPLICIT_LEADER));
+            m_pConfig->getValue<int>(ConfigKey(kBpmConfigGroup, kSyncLockAlgorithmConfigKey),
+                    PREFER_SOFT_LEADER));
     switch (picker) {
-    case PREFER_IMPLICIT_LEADER:
+    case PREFER_SOFT_LEADER:
         // Always pick a deck for a new leader.
         if (playing_deck_count == 1) {
             return first_playing_deck;

src/engine/sync/enginesync.h

@@ -8,12 +8,25 @@
 class InternalClock;
 class EngineChannel;
 
+const QString kBpmConfigGroup = QStringLiteral("[BPM]");
+const QString kSyncLockAlgorithmConfigKey = QStringLiteral("sync_lock_algorithm");
+
 /// EngineSync is the heart of the Mixxx Sync Lock engine.  It knows which objects
 /// (Decks, Internal Clock, etc) are participating in Sync and what their statuses
 /// are. It also orchestrates sync handoffs between different decks as they play,
 /// stop, or request their status to change.
 class EngineSync : public SyncableListener {
   public:
+    // Remove pick SyncLockAlgorithm when new beatgrid detection
+    // and editing code is committed and we no longer need the lock bpm fallback option.
+    enum SyncLockAlgorithm {
+        // New behavior, which should work if beatgrids are reliable.
+        PREFER_SOFT_LEADER,
+        // Old 2.3 behavior, which works around some issues with bad beatgrid detection, mostly
+        // for auto DJ mode.
+        PREFER_LOCK_BPM
+    };
+
     explicit EngineSync(UserSettingsPointer pConfig);
     ~EngineSync() override;
 
@@ -143,17 +156,6 @@ class EngineSync : public SyncableListener {
         return false;
     }
 
-    // TODO: Remove pick algorithms during 2.4 development phase when new beatgrid detection
-    // and editing code is committed and we no longer need the lock bpm fallback option.
-    // If this code makes it to release we will all be very sad.
-    enum SyncLockAlgorithm {
-        // New behavior, which should work if beatgrids are reliable.
-        PREFER_IMPLICIT_LEADER,
-        // Old 2.3 behavior, which works around some issues with bad beatgrid detection, mostly
-        // for auto DJ mode.
-        PREFER_LOCK_BPM
-    };
-
     FRIEND_TEST(EngineSyncTest, EnableOneDeckInitsLeader);
     FRIEND_TEST(EngineSyncTest, EnableOneDeckInitializesLeader);
     FRIEND_TEST(EngineSyncTest, SyncToNonSyncDeck);

src/preferences/dialog/dlgprefdeck.cpp

@@ -6,6 +6,7 @@
 #include "control/controlproxy.h"
 #include "defs_urls.h"
 #include "engine/controls/ratecontrol.h"
+#include "engine/sync/enginesync.h"
 #include "mixer/basetrackplayer.h"
 #include "mixer/playermanager.h"
 #include "moc_dlgprefdeck.cpp"
@@ -259,9 +260,7 @@ DlgPrefDeck::DlgPrefDeck(QWidget* parent, UserSettingsPointer pConfig)
     }
     setRateRangeForAllDecks(m_iRateRangePercent);
 
-    //
     // Key lock mode
-    //
     connect(buttonGroupKeyLockMode,
             QOverload<QAbstractButton*>::of(&QButtonGroup::buttonClicked),
             this,
@@ -274,9 +273,7 @@ DlgPrefDeck::DlgPrefDeck(QWidget* parent, UserSettingsPointer pConfig)
         pControl->set(static_cast<double>(m_keylockMode));
     }
 
-    //
     // Key unlock mode
-    //
     connect(buttonGroupKeyUnlockMode,
             QOverload<QAbstractButton*>::of(&QButtonGroup::buttonClicked),
             this,
@@ -289,21 +286,23 @@ DlgPrefDeck::DlgPrefDeck(QWidget* parent, UserSettingsPointer pConfig)
         pControl->set(static_cast<int>(m_keyunlockMode));
     }
 
-    //
     // Cue Mode
-    //
-
     // Add "(?)" with a manual link to the label
-    labelCueMode->setText(labelCueMode->text() + QStringLiteral(" ") +
+    labelCueMode->setText(labelCueMode->text() + QChar(' ') +
             coloredLinkString(
                     m_pLinkColor,
                     QStringLiteral("(?)"),
                     MIXXX_MANUAL_CUE_MODES_URL));
 
-    //
-    // Speed / Pitch reset configuration
-    //
+    // Sync Mode
+    // Add "(?)" with a manual link to the label
+    labelSyncMode->setText(labelSyncMode->text() + QChar(' ') +
+            coloredLinkString(
+                    m_pLinkColor,
+                    QStringLiteral("(?)"),
+                    MIXXX_MANUAL_SYNC_MODES_URL));
 
+    // Speed / Pitch reset configuration
     // Update "reset speed" and "reset pitch" check boxes
     // TODO: All defaults should only be set in slotResetToDefaults.
     int configSPAutoReset = m_pConfig->getValue<int>(
@@ -457,6 +456,16 @@ void DlgPrefDeck::slotUpdate() {
     index = ComboBoxCueMode->findData(static_cast<int>(cueMode));
     ComboBoxCueMode->setCurrentIndex(index);
 
+    const EngineSync::SyncLockAlgorithm syncLockAlgorithm =
+            static_cast<EngineSync::SyncLockAlgorithm>(m_pConfig->getValue<int>(
+                    ConfigKey(kBpmConfigGroup, kSyncLockAlgorithmConfigKey),
+                    EngineSync::SyncLockAlgorithm::PREFER_SOFT_LEADER));
+    if (syncLockAlgorithm == EngineSync::SyncLockAlgorithm::PREFER_SOFT_LEADER) {
+        radioButtonSoftLeader->setChecked(true);
+    } else {
+        radioButtonLockBpm->setChecked(true);
+    }
+
     KeylockMode keylockMode =
             static_cast<KeylockMode>(static_cast<int>(m_keylockModeControls[0]->get()));
     if (keylockMode == KeylockMode::LockCurrentKey) {
@@ -542,6 +551,8 @@ void DlgPrefDeck::slotResetToDefaults() {
     checkBoxResetSpeed->setChecked(false);
     checkBoxResetPitch->setChecked(true);
 
+    radioButtonSoftLeader->setChecked(true);
+
     radioButtonOriginalKey->setChecked(true);
     radioButtonResetUnlockedKey->setChecked(true);
 }
@@ -721,6 +732,14 @@ void DlgPrefDeck::slotApply() {
     m_pConfig->set(ConfigKey("[Controls]", "SpeedAutoReset"),
                    ConfigValue(configSPAutoReset));
 
+    if (radioButtonSoftLeader->isChecked()) {
+        m_pConfig->setValue(ConfigKey(kBpmConfigGroup, kSyncLockAlgorithmConfigKey),
+                static_cast<int>(EngineSync::SyncLockAlgorithm::PREFER_SOFT_LEADER));
+    } else {
+        m_pConfig->setValue(ConfigKey(kBpmConfigGroup, kSyncLockAlgorithmConfigKey),
+                static_cast<int>(EngineSync::SyncLockAlgorithm::PREFER_LOCK_BPM));
+    }
+
     m_pConfig->setValue(ConfigKey("[Controls]", "keylockMode"),
                         static_cast<int>(m_keylockMode));
     // Set key lock behavior for every group