prevent infinite mixing loops

Prevent infinite mixing loops by disabling the send button for
a channel line when clicking it would cause an infinite loop.

include/FxMixer.h

@@ -97,6 +97,10 @@ public:
 	// delete the connection made by createChannelSend
 	void deleteChannelSend(fx_ch_t fromChannel, fx_ch_t toChannel);
 
+	// determine if adding a send from sendFrom to
+	// sendTo would result in an infinite mixer loop.
+	bool isInfiniteLoop(fx_ch_t fromChannel, fx_ch_t toChannel);
+
 	// return the FloatModel of fromChannel sending its output to the input of
 	// toChannel. NULL if there is no send.
 	FloatModel * channelSendModel(fx_ch_t fromChannel, fx_ch_t toChannel);

src/core/FxMixer.cpp

@@ -158,6 +158,26 @@ void FxMixer::deleteChannelSend(fx_ch_t fromChannel, fx_ch_t toChannel)
 }
 
 
+bool FxMixer::isInfiniteLoop(fx_ch_t sendFrom, fx_ch_t sendTo) {
+	// can't send master to anything
+	if( sendFrom == 0 ) return true;
+
+	// can't send channel to itself
+	if( sendFrom == sendTo ) return true;
+
+	// follow sendTo's outputs recursively looking for something that sends
+	// to sendFrom
+	for(int i=0; i<m_fxChannels[sendTo]->m_sends.size(); ++i)
+	{
+		if( isInfiniteLoop( sendFrom, m_fxChannels[sendTo]->m_sends[i] ) )
+		{
+			return true;
+		}
+	}
+
+	return false;
+}
+
 
 // how much does fromChannel send its output to the input of toChannel?
 FloatModel * FxMixer::channelSendModel(fx_ch_t fromChannel, fx_ch_t toChannel)

src/gui/FxMixerView.cpp

@@ -148,6 +148,8 @@ void FxMixerView::addNewChannel()
 												 newChannelIndex));
 	chLayout->addWidget(m_fxChannelViews[newChannelIndex]->m_fxLine);
 	m_fxRacksLayout->addWidget( m_fxChannelViews[newChannelIndex]->m_rackView );
+
+	updateFxLine(newChannelIndex);
 }
 
 
@@ -207,29 +209,34 @@ void FxMixerView::setCurrentFxLine( FxLine * _line )
 }
 
 
-void FxMixerView::updateFxLine(int i)
+void FxMixerView::updateFxLine(int index)
 {
 	FxMixer * mix = engine::fxMixer();
 
 	// does current channel send to this channel?
-	FloatModel * sendModel = mix->channelSendModel(m_currentFxLine->channelIndex(), i);
+	int selIndex = m_currentFxLine->channelIndex();
+	FxLine * thisLine = m_fxChannelViews[index]->m_fxLine;
+	FloatModel * sendModel = mix->channelSendModel(selIndex, index);
 	if( sendModel == NULL )
 	{
 		// does not send, hide send knob
-		m_fxChannelViews[i]->m_fxLine->m_sendKnob->setVisible(false);
+		thisLine->m_sendKnob->setVisible(false);
 	}
 	else
 	{
 		// it does send, show knob and connect
-		m_fxChannelViews[i]->m_fxLine->m_sendKnob->setVisible(true);
-		m_fxChannelViews[i]->m_fxLine->m_sendKnob->setModel(sendModel);
+		thisLine->m_sendKnob->setVisible(true);
+		thisLine->m_sendKnob->setModel(sendModel);
 	}
 
-
-	m_fxChannelViews[i]->m_fxLine->update();
-	m_fxChannelViews[i]->m_fxLine->m_sendBtn->updateLightStatus();
+	// disable the send button if it would cause an infinite loop
+	thisLine->m_sendBtn->setVisible(! mix->isInfiniteLoop(selIndex, index));
+	thisLine->m_sendBtn->updateLightStatus();
+	thisLine->update();
 }
 
+
+
 void FxMixerView::setCurrentFxLine( int _line )
 {
 	setCurrentFxLine( m_fxChannelViews[_line]->m_fxLine );