Handle various JUCE bus layouts properly (#4562)

1. Handle various JUCE bus layotus properly in isbuseslayoutetc
2. Deal with the consequences at processing time of various
   disabled inputs and outputs

Closes #4462

src/surge_synth_juce/SurgeSynthProcessor.cpp

@@ -144,18 +144,27 @@ void SurgeSynthProcessor::releaseResources()
 
 bool SurgeSynthProcessor::isBusesLayoutSupported(const BusesLayout &layouts) const
 {
-    // the sidechain can take any layout, the main bus needs to be the same on the input and output
-    return layouts.getMainInputChannelSet() == layouts.getMainOutputChannelSet() &&
-           !layouts.getMainInputChannelSet().isDisabled() &&
-           layouts.getMainInputChannelSet() == AudioChannelSet::stereo();
+    auto mocs = layouts.getMainOutputChannelSet();
+    auto mics = layouts.getMainInputChannelSet();
+
+    auto outputValid = (mocs == AudioChannelSet::stereo()) || mocs.isDisabled();
+    auto inputValid = (mics == AudioChannelSet::stereo()) || (mics == AudioChannelSet::mono()) ||
+                      (mics.isDisabled());
+
+    /*
+     * Check the 6 output shape
+     */
+    auto c1 = layouts.getNumChannels(false, 1);
+    auto c2 = layouts.getNumChannels(false, 2);
+    auto sceneOut = (c1 == 0 && c2 == 0) || (c1 == 2 && c2 == 2);
+
+    return outputValid && inputValid && sceneOut;
 }
 
 void SurgeSynthProcessor::processBlock(AudioBuffer<float> &buffer, MidiBuffer &midiMessages)
 {
     auto fpuguard = Surge::CPUFeatures::FPUStateGuard();
 
-    // FIXME obvioulsy
-    float thisBPM = 120.0;
     auto playhead = getPlayHead();
     if (playhead)
     {
@@ -217,20 +226,33 @@ void SurgeSynthProcessor::processBlock(AudioBuffer<float> &buffer, MidiBuffer &m
         }
     }
 
-    auto mainInputOutput = getBusBuffer(buffer, true, 0);
+    // Make sure we have a main output
+    auto mb = getBus(false, 0);
+    if (mb->getNumberOfChannels() != 2 || !mb->isEnabled())
+    {
+        // We have to have a stereo output
+        return;
+    }
+    auto mainOutput = getBusBuffer(buffer, false, 0);
+
+    auto mainInput = getBusBuffer(buffer, true, 0);
     auto sceneAOutput = getBusBuffer(buffer, false, 1);
     auto sceneBOutput = getBusBuffer(buffer, false, 2);
     for (int i = 0; i < buffer.getNumSamples(); i++)
     {
-        auto outL = mainInputOutput.getWritePointer(0, i);
-        auto outR = mainInputOutput.getWritePointer(1, i);
+        auto outL = mainOutput.getWritePointer(0, i);
+        auto outR = mainOutput.getWritePointer(1, i);
 
         surge->time_data.ppqPos += (double)BLOCK_SIZE * surge->time_data.tempo / (60. * samplerate);
 
-        if (blockPos == 0)
+        if (blockPos == 0 && mainInput.getNumChannels() > 0)
         {
-            auto inL = mainInputOutput.getReadPointer(0, i);
-            auto inR = mainInputOutput.getReadPointer(1, i);
+            auto inL = mainInput.getReadPointer(0, i);
+            auto inR = inL;                     // assume mono
+            if (mainInput.getNumChannels() > 1) // unless its not
+            {
+                inR = mainInput.getReadPointer(1, i);
+            }
             surge->process_input = true;
             memcpy(&(surge->input[0][0]), inL, BLOCK_SIZE * sizeof(float));
             memcpy(&(surge->input[1][0]), inR, BLOCK_SIZE * sizeof(float));