Handle various JUCE bus layouts properly

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

Closes surge-synthesizer#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));