From 441fd905bee745a56de6f838812584306daa6add Mon Sep 17 00:00:00 2001
From: Sotonye Atemie <sakertooth@gmail.com>
Date: Mon, 9 Feb 2026 11:57:28 -0500
Subject: [PATCH] Improve performance when moving channels in the Mixer (#8235)

Improves performance when moving mixer channels to the left or right using simple Qt layout operations and swapping of values. This commit also addresses a deadlock in Mixer::mixToChannel by ensuring we lock and unlock the same channel regardless of any move operations occurring simultaneously on another thread.
---
 include/MixerChannelView.h   |  1 +
 include/MixerView.h          |  1 -
 src/core/Mixer.cpp           | 11 +++++-----
 src/gui/MixerChannelView.cpp |  6 ------
 src/gui/MixerView.cpp        | 39 ++++++++++++++----------------------
 5 files changed, 22 insertions(+), 36 deletions(-)

diff --git a/include/MixerChannelView.h b/include/MixerChannelView.h
index 1b2fa3953..6f2217012 100644
--- a/include/MixerChannelView.h
+++ b/include/MixerChannelView.h
@@ -64,6 +64,7 @@ public:
 	void keyPressEvent(QKeyEvent* ke) override;
 
 	void reset();
+
 	int channelIndex() const { return m_channelIndex; }
 	void setChannelIndex(int index);
 
diff --git a/include/MixerView.h b/include/MixerView.h
index f5f98b62a..6d9fded64 100644
--- a/include/MixerView.h
+++ b/include/MixerView.h
@@ -83,7 +83,6 @@ public:
 
 	// move the channel to the left or right
 	void moveChannelLeft(int index);
-	void moveChannelLeft(int index, int focusIndex);
 	void moveChannelRight(int index);
 
 	void renameChannel(int index);
diff --git a/src/core/Mixer.cpp b/src/core/Mixer.cpp
index 6007be466..156987336 100644
--- a/src/core/Mixer.cpp
+++ b/src/core/Mixer.cpp
@@ -644,12 +644,13 @@ FloatModel * Mixer::channelSendModel( mix_ch_t fromChannel, mix_ch_t toChannel )
 
 void Mixer::mixToChannel( const SampleFrame* _buf, mix_ch_t _ch )
 {
-	if( m_mixerChannels[_ch]->m_muteModel.value() == false )
+	const auto channel = m_mixerChannels[_ch];
+	if (!channel->m_muteModel.value())
 	{
-		m_mixerChannels[_ch]->m_lock.lock();
-		MixHelpers::add( m_mixerChannels[_ch]->m_buffer, _buf, Engine::audioEngine()->framesPerPeriod() );
-		m_mixerChannels[_ch]->m_hasInput = true;
-		m_mixerChannels[_ch]->m_lock.unlock();
+		channel->m_lock.lock();
+		MixHelpers::add(channel->m_buffer, _buf, Engine::audioEngine()->framesPerPeriod());
+		channel->m_hasInput = true;
+		channel->m_lock.unlock();
 	}
 }
 
diff --git a/src/gui/MixerChannelView.cpp b/src/gui/MixerChannelView.cpp
index d3de94bef..26b2aa94c 100644
--- a/src/gui/MixerChannelView.cpp
+++ b/src/gui/MixerChannelView.cpp
@@ -249,13 +249,7 @@ void MixerChannelView::keyPressEvent(QKeyEvent* ke)
 
 void MixerChannelView::setChannelIndex(int index)
 {
-	MixerChannel* mixerChannel = Engine::mixer()->mixerChannel(index);
-	m_fader->setModel(&mixerChannel->m_volumeModel);
-	m_muteButton->setModel(&mixerChannel->m_muteModel);
-	m_soloButton->setModel(&mixerChannel->m_soloModel);
-	m_effectRackView->setModel(&mixerChannel->m_fxChain);
 	m_channelNumberLcd->setValue(index);
-	m_renameLineEdit->setText(elideName(mixerChannel->m_name));
 	m_channelIndex = index;
 }
 
diff --git a/src/gui/MixerView.cpp b/src/gui/MixerView.cpp
index 299f1bff5..ef1f35a20 100644
--- a/src/gui/MixerView.cpp
+++ b/src/gui/MixerView.cpp
@@ -433,38 +433,29 @@ void MixerView::deleteUnusedChannels()
 	}
 }
 
-
-
-void MixerView::moveChannelLeft(int index, int focusIndex)
-{
-	// can't move master or first channel left or last channel right
-	if (index <= 1 || index >= m_mixerChannelViews.size()) return;
-
-	Mixer *m = getMixer();
-
-	// Move instruments channels
-	m->moveChannelLeft(index);
-
-	// Update widgets models
-	m_mixerChannelViews[index]->setChannelIndex(index);
-	m_mixerChannelViews[index - 1]->setChannelIndex(index - 1);
-
-	// Focus on new position
-	setCurrentMixerChannel(focusIndex);
-}
-
-
-
 void MixerView::moveChannelLeft(int index)
 {
-	moveChannelLeft(index, index - 1);
+	// can't move master or first channel left or last channel right
+	if (index <= 1 || index >= m_mixerChannelViews.size()) { return; }
+
+	m_mixer->moveChannelLeft(index);
+
+	const auto layoutIndex = chLayout->indexOf(m_mixerChannelViews[index]);
+	assert(layoutIndex >= 1);
+
+	chLayout->removeWidget(m_mixerChannelViews[index]);
+	chLayout->insertWidget(layoutIndex - 1, m_mixerChannelViews[index]);
+
+	m_mixerChannelViews[index]->setChannelIndex(index - 1);
+	m_mixerChannelViews[index - 1]->setChannelIndex(index);
+	std::swap(m_mixerChannelViews[index - 1], m_mixerChannelViews[index]);
 }
 
 
 
 void MixerView::moveChannelRight(int index)
 {
-	moveChannelLeft(index + 1, index + 1);
+	moveChannelLeft(index + 1);
 }