From a0452eeb57d5acf5db795dec5f303038963ba85c Mon Sep 17 00:00:00 2001
From: Robin Gareus <robin@gareus.org>
Date: Fri, 6 Jan 2023 03:08:05 +0100
Subject: [PATCH] VST3: dynamically grow ParameterChanges

Some plugins (e.g. Roland JD-800) have zero controls, but
MIDI control with are not directly accounted for. This
results in a zero-size ParameterChanges queue, which later produced
a segfault when trying to enqueue a MIDI change:

```
input_param_changes.addParameterData (id, index)->addPoint (sample_off, value, index);
```
---
 libs/ardour/vst3_host.cc   | 17 +++++++++++------
 libs/ardour/vst3_plugin.cc |  6 ++++++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/libs/ardour/vst3_host.cc b/libs/ardour/vst3_host.cc
index 37ec59554f..78ecbf8b6f 100644
--- a/libs/ardour/vst3_host.cc
+++ b/libs/ardour/vst3_host.cc
@@ -585,13 +585,18 @@ Vst3ParameterChanges::addParameterData (Vst::ParamID const& pid, int32& index)
 		}
 	}
 
-	if (_used_queue_count < (int32)_queue.size ()) {
-		index = _used_queue_count++;
-		_queue[index].setParameterId (pid);
-		return &_queue[index];
+	/* some plugins (e.g. Roland JD-800) have zero controls
+	 * (set_n_params (0)) but MIDI controls (which are not accounted for).
+	 * So we grow the list as needed. NB. It is not rt-safe to do so, but it
+	 * only happens once initially.
+	 */
+	if (_used_queue_count >= (int32)_queue.size ()) {
+		_queue.resize (_used_queue_count + 1);
 	}
-	index = 0;
-	return 0;
+
+	index = _used_queue_count++;
+	_queue[index].setParameterId (pid);
+	return &_queue[index];
 }
 
 /* ****************************************************************************/
diff --git a/libs/ardour/vst3_plugin.cc b/libs/ardour/vst3_plugin.cc
index 362c189964..37fe11f1ba 100644
--- a/libs/ardour/vst3_plugin.cc
+++ b/libs/ardour/vst3_plugin.cc
@@ -1230,6 +1230,12 @@ VST3PI::VST3PI (boost::shared_ptr<ARDOUR::VST3PluginModule> m, std::string uniqu
 		_update_ctrl.push_back (false);
 	}
 
+	if (_n_midi_inputs > 0 || _n_midi_outputs > 0) {
+		n_params += 128;
+	} else if (n_params == 0) {
+		n_params = 16; /* arbitrary baseline, grows as needed */
+	}
+
 	_input_param_changes.set_n_params (n_params);
 	_output_param_changes.set_n_params (n_params);