Add minimal boilerplate for a CLAP plugin

src/plugin/clap-plugin.cpp

@@ -0,0 +1,57 @@
+// yabridge: a Wine plugin bridge
+// Copyright (C) 2020-2022 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/>.
+
+#include <atomic>
+
+#include <clap/entry.h>
+
+/**
+ * The number of active instances. Incremented when `clap_entry_init()` is
+ * called, decremented when `clap_entry_exit()` is called. We'll initialize the
+ * bridge when this is first incremented from 0, and we'll free the bridge again
+ * when a `clap_entry_exit()` call causes this to return back to 0.
+ */
+std::atomic_size_t active_instances = 0;
+
+bool clap_entry_init(const char* plugin_path) {
+    // This function can be called multiple times, so we should make sure to
+    // only initialize the bridge on the first call
+    if (active_instances.fetch_add(1, std::memory_order_seq_cst) == 0) {
+        // TODO: Increase reference count, init factory if it was zero
+    }
+
+    return true;
+}
+
+void clap_entry_deinit() {
+    // We'll free the bridge when this exits brings the reference count back to
+    // zero
+    if (active_instances.fetch_sub(1, std::memory_order_seq_cst) == 1) {
+        // TODO: Destroy the bridge instance
+    }
+}
+
+const void* clap_entry_get_factory(const char* factory_id) {
+    // TODO: Do the thing
+    // TODO: Assertion
+}
+
+CLAP_EXPORT const clap_plugin_entry_t clap_entry = {
+    .clap_version = CLAP_VERSION_INIT,
+    .init = clap_entry_init,
+    .deinit = clap_entry_deinit,
+    .get_factory = clap_entry_get_factory,
+};

src/plugin/meson.build

@@ -14,6 +14,22 @@ vst2_plugin_deps = [
   tomlplusplus_dep,
 ]
 
+if with_clap
+  clap_plugin_deps = [
+    configuration_dep,
+
+    asio_dep,
+    bitsery_dep,
+    clap_dep,
+    dl_dep,
+    function2_dep,
+    ghc_filesystem_dep,
+    rt_dep,
+    threads_dep,
+    tomlplusplus_dep,
+  ]
+endif
+
 if with_vst3
   vst3_plugin_deps = [
     configuration_dep,
@@ -50,6 +66,12 @@ vst2_plugin_sources = files(
   'vst2-plugin.cpp',
 )
 
+if with_clap
+  clap_plugin_sources = files(
+    'clap-plugin.cpp',
+  )
+endif
+
 if with_vst3
   vst3_plugin_sources = files(
     '../common/communication/common.cpp',