Add an IConnectionPoint proxy proxy

This is a bit dumb, but this way we can support indirectly connected
objects.

src/common/serialization/vst3/connection-point-proxy.h

@@ -0,0 +1,104 @@
+// yabridge: a Wine VST bridge
+// Copyright (C) 2020  Robbert van der Helm
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include "../common.h"
+#include "plugin/connection-point.h"
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wnon-virtual-dtor"
+
+/**
+ * This is only needed to...proxy a connection point proxy. Most hosts will
+ * connect a plugin's processor and controller directly using
+ * `IConnectionPoint::connect()`. But some hosts, like Ardour, will place a
+ * proxy object between them that forwards calls to
+ * `IConnectionPoint::notify()`. When objects are connected directly by the host
+ * we can also connect them directly in the Wine plugin host, but when the host
+ * uses proxies we'll also have to go through that proxy. The purpose of this
+ * class is to provide a proxy for such a connection proxy. So when the plugin
+ * calls `notify()` on an object of this class, then we will forward that call
+ * to the `IConnectionPoint` proxy provided by the host, which will then in turn
+ * call `IConnectionPoint::notify()` on the other object and we'll then forward
+ * that message again to them Wine plugin host.
+ */
+class Vst3ConnectionPointProxy : public YaConnectionPoint {
+   public:
+    /**
+     * These are the arguments for constructing a
+     * `Vst3ConnectionPointProxyImpl`.
+     */
+    struct ConstructArgs {
+        ConstructArgs();
+
+        /**
+         * Read from an existing object. We will try to mimic this object, so
+         * we'll support any interfaces this object also supports.
+         *
+         * This is not necessary in this case since the object has to support
+         * `IConnectionPoint`, but let's stay consistent with the overall style
+         * here.
+         */
+        ConstructArgs(Steinberg::IPtr<FUnknown> object,
+                      size_t owner_instance_id);
+
+        /**
+         * The unique instance identifier of the proxy object instance this
+         * connection proxy has been passed to and thus belongs to. This way we
+         * can refer to the correct 'actual' `IConnectionPoint` instance when
+         * the plugin calls `notify()` on this proxy object.
+         */
+        native_size_t owner_instance_id;
+
+        YaConnectionPoint::ConstructArgs connection_point_args;
+
+        template <typename S>
+        void serialize(S& s) {
+            s.value8b(owner_instance_id);
+            s.object(connection_point_args);
+        }
+    };
+
+    /**
+     * Instantiate this instance with arguments read from an actual
+     * `IConnectionPoint` object/proxy.
+     *
+     * @note This object will be created as part of handling
+     *   `IConnectionPoint::connect()` if the connection is indirect.
+     */
+    Vst3ConnectionPointProxy(const ConstructArgs&& args);
+
+    /**
+     * This object will be destroyed again during
+     * `IConnectionPoint::disconnect()`.
+     */
+    virtual ~Vst3ConnectionPointProxy();
+
+    DECLARE_FUNKNOWN_METHODS
+
+    /**
+     * Get the instance ID of the owner of this object.
+     */
+    inline size_t owner_instance_id() const {
+        return arguments.owner_instance_id;
+    }
+
+   private:
+    ConstructArgs arguments;
+};
+
+#pragma GCC diagnostic pop