Decouple tracks from the Mixer

include/AutomatableModel.h

@@ -144,6 +144,7 @@ class LMMS_EXPORT AutomatableModel : public Model, public JournallingObject
 		return (std::round(v) != 0);
 	}
 
+	float oldValue() const { return m_oldValue; }
 
 	template<class T>
 	inline T value( int frameOffset = 0 ) const

include/InstrumentTrack.h

@@ -26,20 +26,19 @@
 #ifndef LMMS_INSTRUMENT_TRACK_H
 #define LMMS_INSTRUMENT_TRACK_H
 
-
 #include "AudioBusHandle.h"
 #include "InstrumentFunctions.h"
 #include "InstrumentSoundShaping.h"
 #include "Microtuner.h"
 #include "Midi.h"
 #include "MidiEventProcessor.h"
 #include "MidiPort.h"
+#include "MixerChannelLcdModel.h"
 #include "NotePlayHandle.h"
 #include "Piano.h"
 #include "Plugin.h"
 #include "Track.h"
 
-
 namespace lmms
 {
 
@@ -262,7 +261,6 @@ protected slots:
 	void updatePitchRange();
 	void updateMixerChannel();
 
-
 private:
 	void processCCEvent(int controller);
 
@@ -296,7 +294,7 @@ protected slots:
 
 	FloatModel m_pitchModel;
 	IntModel m_pitchRangeModel;
-	IntModel m_mixerChannelModel;
+	MixerChannelLcdModel m_mixerChannelModel;
 	BoolModel m_useMasterPitchModel;
 
 	Instrument * m_instrument;

include/Mixer.h

@@ -88,9 +88,15 @@ class MixerChannel : public ThreadableJob
 	void incrementDeps();
 	void processed();
 
+	int useCount() const { return m_useCount; }
+
+	void incrementUseCount() { ++m_useCount; }
+	void decrementUseCount() { --m_useCount; }
+
 private:
 	void doProcessing() override;
 	int m_channelIndex;
+	int m_useCount;
 	std::optional<QColor> m_color;
 };
 
@@ -214,6 +220,11 @@ class LMMS_EXPORT Mixer : public Model, public JournallingObject
 
 	MixerRouteVector m_mixerRoutes;
 
+signals:
+	void channelCreated(int index);
+	void channelDeleted(int index);
+	void channelsSwapped(int fromIndex, int toIndex);
+
 private:
 	// the mixer channels in the mixer. index 0 is always master.
 	std::vector<MixerChannel*> m_mixerChannels;

include/MixerChannelLcdModel.h

@@ -0,0 +1,56 @@
+/*
+ * MixerChannelLcdModel.h
+ *
+ * Copyright (c) 2026 saker <sakertooth@gmail.com>
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef LMMS_MIXER_CHANNEL_LCD_MODEL_H
+#define LMMS_MIXER_CHANNEL_LCD_MODEL_H
+
+#include "AutomatableModel.h"
+
+namespace lmms {
+/**
+ * @brief An @ref IntModel that keeps track of its assigned mixer channel.
+ * 
+ * This model tracks its assigned mixer channel. It is a subclass of IntModel that adds functionality to handle channel
+ * creation, deletion, and swapping. Both the value and valid range are automatically updated to reflect these changes.
+ */
+class MixerChannelLcdModel : public IntModel
+{
+public:
+	MixerChannelLcdModel(Model* parent = nullptr);
+	~MixerChannelLcdModel();
+
+	MixerChannelLcdModel(const MixerChannelLcdModel&) = delete;
+	MixerChannelLcdModel(MixerChannelLcdModel&&) = delete;
+	MixerChannelLcdModel& operator=(const MixerChannelLcdModel&) = delete;
+	MixerChannelLcdModel& operator=(MixerChannelLcdModel&&) = delete;
+
+private:
+	void channelsSwapped(int fromIndex, int toIndex);
+	void channelDeleted(int index);
+	void channelCreated(int index);
+};
+
+} // namespace lmms
+
+#endif // LMMS_MIXER_CHANNEL_LCD_MODEL_H

include/MixerView.h

@@ -123,8 +123,6 @@ private slots:
 	QWidget* m_racksWidget;
 	Mixer* m_mixer;
 
-	void updateMaxChannelSelector();
-
 	friend class MixerChannelView;
 } ;
 

include/SampleTrack.h

@@ -26,6 +26,7 @@
 #define LMMS_SAMPLE_TRACK_H
 
 #include "AudioBusHandle.h"
+#include "MixerChannelLcdModel.h"
 #include "Track.h"
 
 
@@ -94,7 +95,7 @@ public slots:
 private:
 	FloatModel m_volumeModel;
 	FloatModel m_panningModel;
-	IntModel m_mixerChannelModel;
+	MixerChannelLcdModel m_mixerChannelModel;
 	AudioBusHandle m_audioBusHandle;
 	bool m_isPlaying;
 

src/core/CMakeLists.txt

@@ -45,6 +45,7 @@ set(LMMS_SRCS
 	core/MicroTimer.cpp
 	core/Microtuner.cpp
 	core/MixHelpers.cpp
+	core/MixerChannelLcdModel.cpp
 	core/Model.cpp
 	core/ModelVisitor.cpp
 	core/Note.cpp

src/core/Mixer.cpp

@@ -70,7 +70,8 @@ MixerChannel::MixerChannel( int idx, Model * _parent ) :
 	m_lock(),
 	m_queued( false ),
 	m_dependenciesMet(0),
-	m_channelIndex(idx)
+	m_channelIndex(idx),
+	m_useCount(0)
 {
 	m_buffer.allocateInterleavedBuffer();
 }
@@ -271,6 +272,7 @@ int Mixer::createChannel()
 		m_mixerChannels[index]->m_muteModel.setValue(true);
 	}
 
+	emit channelCreated(index);
 	return index;
 }
 
@@ -331,50 +333,6 @@ void Mixer::deleteChannel( int index )
 	// channel deletion is performed between mixer rounds
 	Engine::audioEngine()->requestChangeInModel();
 
-	// go through every instrument and adjust for the channel index change
-	TrackContainer::TrackList tracks;
-
-	auto& songTracks = Engine::getSong()->tracks();
-	auto& patternStoreTracks = Engine::patternStore()->tracks();
-	tracks.insert(tracks.end(), songTracks.begin(), songTracks.end());
-	tracks.insert(tracks.end(), patternStoreTracks.begin(), patternStoreTracks.end());
-
-	for( Track* t : tracks )
-	{
-		if( t->type() == Track::Type::Instrument )
-		{
-			auto inst = dynamic_cast<InstrumentTrack*>(t);
-			int val = inst->mixerChannelModel()->value(0);
-			if( val == index )
-			{
-				// we are deleting this track's channel send
-				// send to master
-				inst->mixerChannelModel()->setValue(0);
-			}
-			else if( val > index )
-			{
-				// subtract 1 to make up for the missing channel
-				inst->mixerChannelModel()->setValue(val-1);
-			}
-		}
-		else if( t->type() == Track::Type::Sample )
-		{
-			auto strk = dynamic_cast<SampleTrack*>(t);
-			int val = strk->mixerChannelModel()->value(0);
-			if( val == index )
-			{
-				// we are deleting this track's channel send
-				// send to master
-				strk->mixerChannelModel()->setValue(0);
-			}
-			else if( val > index )
-			{
-				// subtract 1 to make up for the missing channel
-				strk->mixerChannelModel()->setValue(val-1);
-			}
-		}
-	}
-
 	MixerChannel * ch = m_mixerChannels[index];
 
 	// delete all of this channel's sends and receives
@@ -414,6 +372,8 @@ void Mixer::deleteChannel( int index )
 		}
 	}
 
+	emit channelDeleted(index);
+
 	Engine::audioEngine()->doneChangeInModel();
 }
 
@@ -422,60 +382,23 @@ void Mixer::deleteChannel( int index )
 void Mixer::moveChannelLeft( int index )
 {
 	// can't move master or first channel
-	if (index <= 1 || static_cast<std::size_t>(index) >= m_mixerChannels.size())
-	{
-		return;
-	}
+	if (index <= 1 || static_cast<std::size_t>(index) >= m_mixerChannels.size()) { return; }
+
 	// channels to swap
 	int a = index - 1, b = index;
 
 	// check if m_lastSoloed is one of our swaps
 	if (m_lastSoloed == a) { m_lastSoloed = b; }
 	else if (m_lastSoloed == b) { m_lastSoloed = a; }
 
-	// go through every instrument and adjust for the channel index change
-	const TrackContainer::TrackList& songTrackList = Engine::getSong()->tracks();
-	const TrackContainer::TrackList& patternTrackList = Engine::patternStore()->tracks();
-
-	for (const auto& trackList : {songTrackList, patternTrackList})
-	{
-		for (const auto& track : trackList)
-		{
-			if (track->type() == Track::Type::Instrument)
-			{
-				auto inst = (InstrumentTrack*)track;
-				int val = inst->mixerChannelModel()->value(0);
-				if( val == a )
-				{
-					inst->mixerChannelModel()->setValue(b);
-				}
-				else if( val == b )
-				{
-					inst->mixerChannelModel()->setValue(a);
-				}
-			}
-			else if (track->type() == Track::Type::Sample)
-			{
-				auto strk = (SampleTrack*)track;
-				int val = strk->mixerChannelModel()->value(0);
-				if( val == a )
-				{
-					strk->mixerChannelModel()->setValue(b);
-				}
-				else if( val == b )
-				{
-					strk->mixerChannelModel()->setValue(a);
-				}
-			}
-		}
-	}
-
 	// Swap positions in array
-	qSwap(m_mixerChannels[index], m_mixerChannels[index - 1]);
+	std::swap(m_mixerChannels[index], m_mixerChannels[index - 1]);
 
 	// Update m_channelIndex of both channels
 	m_mixerChannels[index]->setIndex(index);
 	m_mixerChannels[index - 1]->setIndex(index - 1);
+
+	emit channelsSwapped(index, index - 1);
 }
 
 
@@ -891,41 +814,12 @@ void Mixer::validateChannelName( int index, int oldIndex )
 
 bool Mixer::isChannelInUse(int index)
 {
-	// check if the index mixer channel receives audio from any other channel
-	if (!m_mixerChannels[index]->m_receives.empty())
-	{
-		return true;
-	}
+	assert(index >= 0 && index < m_mixerChannels.size());
 
-	// check if the destination mixer channel on any instrument or sample track is the index mixer channel
-	TrackContainer::TrackList tracks;
-
-	auto& songTracks = Engine::getSong()->tracks();
-	auto& patternStoreTracks = Engine::patternStore()->tracks();
-	tracks.insert(tracks.end(), songTracks.begin(), songTracks.end());
-	tracks.insert(tracks.end(), patternStoreTracks.begin(), patternStoreTracks.end());
-
-	for (const auto t : tracks)
-	{
-		if (t->type() == Track::Type::Instrument)
-		{
-			auto inst = dynamic_cast<InstrumentTrack*>(t);
-			if (inst->mixerChannelModel()->value() == index)
-			{
-				return true;
-			}
-		}
-		else if (t->type() == Track::Type::Sample)
-		{
-			auto strack = dynamic_cast<SampleTrack*>(t);
-			if (strack->mixerChannelModel()->value() == index)
-			{
-				return true;
-			}
-		}
-	}
+	// check if the index mixer channel receives audio from any other channel
+	if (!m_mixerChannels[index]->m_receives.empty()) { return true; }
 
-	return false;
+	return m_mixerChannels[index]->useCount() > 0;
 }