Group Processor Ringout support (surge-synthesizer#1176)

This adds support for a processor to implement tailLength
and then keep a group alie through its tail. it also adds a
reasonable tailLength implementation to ShortDelay (but no
other processor).

Addresses surge-synthesizer#852. Once we do the same with EG12 release that
issue will be mostly wrapped, but we do need to visit all the procs for
a tail.

src/dsp/processor/processor.h

@@ -294,9 +294,11 @@ struct Processor : MoveableOnly<Processor>, SampleRateSupport
         assert(false);
     }
 
-    // processors are required to be able to process stereo blocks if stereo is true in the
-    // constructor
     virtual void suspend() {}
+
+    /*
+     * Tail length in samples
+     */
     virtual int tail_length() { return 0; }
 
     float modulation_output; // processors can use this to output modulation data to the matrix

src/engine/group.cpp

@@ -260,6 +260,16 @@ template <bool OS> void Group::processWithOS(scxt::engine::Engine &e)
     {
         osDownFilter.process_block_D2(lOut, rOut, blockSize << 1);
     }
+    if (activeZones == 0)
+    {
+        ringoutTime += blockSize;
+        updateRingout();
+        if (ringoutTime >= ringoutMax)
+        {
+            mUILag.instantlySnap();
+            parentPart->removeActiveGroup();
+        }
+    }
 }
 
 void Group::addActiveZone()
@@ -269,7 +279,40 @@ void Group::addActiveZone()
         parentPart->addActiveGroup();
         attack();
     }
+    // Important we do this *after* the attack since it allows
+    // isActive to be accurate with processor ringout
     activeZones++;
+    ringoutTime = 0;
+}
+
+bool Group::updateRingout()
+{
+    auto res{false};
+    int32_t mx{0};
+    for (auto &p : processors)
+    {
+        if (!p)
+            continue;
+        auto tl = p->tail_length();
+        if (tl != 0)
+        {
+            if (tl == -1)
+            {
+                /*
+                 * Someone is infinite. So set ringout time to 0
+                 * then if someone drops away from infinite we start
+                 * counting at their max
+                 */
+                mx = std::numeric_limits<int32_t>::max();
+                ringoutTime = 0;
+            }
+            else
+                mx = std::max(mx, tl);
+            res = true;
+        }
+    }
+    ringoutMax = mx;
+    return res;
 }
 
 void Group::removeActiveZone()
@@ -278,8 +321,14 @@ void Group::removeActiveZone()
     activeZones--;
     if (activeZones == 0)
     {
-        mUILag.instantlySnap();
-        parentPart->removeActiveGroup();
+        ringoutMax = 0;
+        ringoutTime = 0;
+        auto hasRingout = updateRingout();
+        if (!hasRingout)
+        {
+            mUILag.instantlySnap();
+            parentPart->removeActiveGroup();
+        }
     }
 }
 
@@ -365,6 +414,13 @@ void Group::onProcessorTypeChanged(int w, dsp::processor::ProcessorType t)
 
 void Group::attack()
 {
+    if (isActive())
+    {
+        // I *thin* we need to do this
+        rePrepareAndBindGroupMatrix();
+        return;
+    }
+
     for (int i = 0; i < processorsPerZoneAndGroup; ++i)
     {
         const auto &ps = processorStorage[i];
@@ -380,6 +436,10 @@ void Group::attack()
     osDownFilter.reset();
     resetLFOs();
     rePrepareAndBindGroupMatrix();
+
+    for (auto p : processors)
+        if (p)
+            p->init();
 }
 
 void Group::resetLFOs(int whichLFO)
@@ -417,5 +477,15 @@ void Group::resetLFOs(int whichLFO)
     }
 }
 
+bool Group::isActive() const
+{
+    const auto az = activeZones != 0;
+    const auto procRO = ringoutTime < ringoutMax;
+
+    // structuring it so we can do AEG and env LFO shortly also
+
+    return az || procRO;
+}
+
 template struct HasGroupZoneProcessors<Group>;
 } // namespace scxt::engine

src/engine/group.h

@@ -152,7 +152,7 @@ struct Group : MoveableOnly<Group>,
         return res;
     }
 
-    bool isActive() { return activeZones != 0; }
+    bool isActive() const;
     void addActiveZone();
     void removeActiveZone();
 
@@ -204,6 +204,10 @@ struct Group : MoveableOnly<Group>,
     void onProcessorTypeChanged(int w, dsp::processor::ProcessorType t);
 
     uint32_t activeZones{0};
+    int32_t ringoutTime{0};
+    int32_t ringoutMax{0};
+
+    bool updateRingout();
 
     typedef std::vector<std::unique_ptr<Zone>> zoneContainer_t;