Extend the lifetime of MIDI events, fixing Kontakt

README.md

@@ -20,7 +20,6 @@ There are a few things that should be done before releasing this, including:
     that do this. Not sure if this is fixable in yabridge.
   - Serum crashed and audio engine froze while browsing through Serum presets in
     the browser?
-  - No midi input in Kontakt.
   - Polish GUIs even further. There are some todos left in
     `src/wine-host/editor.{h,cpp}`.
 - Add missing details if any to the architecture section.

src/wine-host/plugin-bridge.cpp

@@ -16,6 +16,8 @@
 
 #include "plugin-bridge.h"
 
+#include <iostream>
+
 #include <boost/filesystem.hpp>
 
 #include "../common/communication.h"
@@ -157,8 +159,43 @@ void PluginBridge::handle_dispatch() {
 
 [[noreturn]] void PluginBridge::handle_dispatch_midi_events() {
     while (true) {
-        passthrough_event(host_vst_dispatch_midi_events, std::nullopt, plugin,
+        // TODO: Refactor `passthrough_event()` to factor out the data
-                          plugin->dispatcher);
+        //       conversion specifically for this case so we don't have to do
+        //       this `DynamicVstEvents -> VstEvents -> void* ->
+        //       DynamicVstEvents -> VstEvents -> void*` conversion dance
+        passthrough_event(
+            host_vst_dispatch_midi_events, std::nullopt, plugin,
+            [&](AEffect* plugin, int opcode, int index, intptr_t value,
+                void* data, float option) {
+                if (BOOST_LIKELY(opcode == effProcessEvents)) {
+                    // For 99% of the plugins we can just call
+                    // `effProcessReplacing()` and be done with it, but a select
+                    // few plugins (I could only find Kontakt that does this)
+                    // don't actually make copies of the events they receive and
+                    // only store pointers, meaning that they have to live at
+                    // least until the next audio buffer gets processed. This
+                    // does mean that we have to reconstruct the
+                    // `DynamicVstEvents` object first.
+                    // HACK: Is there a cleaner way to do this, or a way to
+                    //       avoid having to store temporary copies of this?
+                    DynamicVstEvents* events;
+                    {
+                        std::lock_guard lock(next_buffer_midi_events_mutex);
+                        events = &next_audio_buffer_midi_events.emplace_back(
+                            *static_cast<const VstEvents*>(data));
+                    }
+
+                    return plugin->dispatcher(plugin, opcode, index, value,
+                                              &events->as_c_events(), option);
+                } else {
+                    std::cerr << "[Warning] Received non-midi "
+                                 "event on midi processing thread"
+                              << std::endl;
+
+                    return dispatch_wrapper(plugin, opcode, index, value, data,
+                                            option);
+                }
+            });
     }
 }
 
@@ -210,9 +247,16 @@ void PluginBridge::handle_dispatch() {
             outputs.push_back(buffer.data());
         }
 
+        // Let the plugin process the midi events that were received since the
+        // last buffer, and then clean up those events. This approach should not
+        // be needed but Kontakt only stores pointers to rather than copies of
+        // the events.
+        {
+            std::lock_guard lock(next_buffer_midi_events_mutex);
+
             // Any plugin made in the last fifteen years or so should support
-        // `processReplacing`. In the off chance it does not we can just emulate
+            // `processReplacing`. In the off chance it does not we can just
-        // this behavior ourselves.
+            // emulate this behavior ourselves.
             if (plugin->processReplacing != nullptr) {
                 plugin->processReplacing(plugin, inputs.data(), outputs.data(),
                                          request.sample_frames);
@@ -227,6 +271,9 @@ void PluginBridge::handle_dispatch() {
                                 request.sample_frames);
             }
 
+            next_audio_buffer_midi_events.clear();
+        }
+
         AudioBuffers response{output_buffers, request.sample_frames};
         write_object(host_vst_process_replacing, response, process_buffer);
     }

src/wine-host/plugin-bridge.h

@@ -168,6 +168,20 @@ class PluginBridge {
      */
     std::vector<uint8_t> process_buffer;
 
+    /**
+     * The MIDI events that have been received **and processed** since the last
+     * call to `processReplacing()`. 99% of plugins make a copy of the MIDI
+     * events they receive but some plugins such as Kontakt only store pointers
+     * to these events, which means that the actual `VstEvent` objects must live
+     * at least until the next audio buffer gets processed.
+     */
+    std::vector<DynamicVstEvents> next_audio_buffer_midi_events;
+    /**
+     * Mutex for locking the above event queue, since recieving and processing
+     * now happens in two different threads.
+     */
+    std::mutex next_buffer_midi_events_mutex;
+
     /**
      * The plugin editor window. Allows embedding the plugin's editor into a
      * Wine window, and embedding that Wine window into a window provided by the