Add a plugin state converter factory

include/clap/factory/draft/plugin-state-converter.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include "../../id.h"
+#include "../../plugin-id.h"
+#include "../../stream.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// This interface provides helps the host to convert a plugin state and its automation
+// points to a new plugin.
+//
+// This is useful to convert from one plugin ABI to another one.
+// This is also useful to offer an upgrade path: from EQ version 1 to EQ version 2.
+// This can also be used to convert the state of a plugin that isn't maintained anymore into
+// another plugin that would be similar.
+typedef struct clap_plugin_state_converter {
+   const clap_plugin_id_t *src_plugin_id;
+   const clap_plugin_id_t *dst_plugin_id;
+
+   // Converts the input state to a state usable by the destination plugin.
+   // [thread-safe]
+   bool (*convert_state)(const struct clap_plugin_state_converter *converter,
+                         const clap_istream_t                     *src,
+                         const clap_ostream_t                     *dst);
+
+   // Converts a normalized value.
+   // [thread-safe]
+   bool (*convert_normalized_value)(const struct clap_plugin_state_converter *converter,
+                                    clap_id                                   src_param_id,
+                                    double                                    src_normalized_value,
+                                    clap_id                                  *dst_param_id,
+                                    double                                   *dst_normalized_value);
+
+   // Converts a plain value.
+   // [thread-safe]
+   bool (*convert_plain_value)(const struct clap_plugin_state_converter *converter,
+                               clap_id                                   src_param_id,
+                               double                                    src_plain_value,
+                               clap_id                                  *dst_param_id,
+                               double                                   *dst_plain_value);
+} clap_plugin_state_converter_t;
+
+// Factory identifier
+static CLAP_CONSTEXPR const char CLAP_CLAP_CONVERTER_FACTORY_ID[] =
+   "clap.plugin-state-converter-factory/1";
+
+// List all the plugin state converters available in the current DSO.
+typedef struct clap_plugin_state_converter_factory {
+   // Get the number of converters.
+   // [thread-safe]
+   uint32_t (*count)(const struct clap_plugin_state_converter_factory *factory);
+
+   // Get the converter at the given index.
+   // [thread-safe]
+   const clap_plugin_state_converter_t *(*get)(
+      const struct clap_plugin_state_converter_factory *factory, uint32_t index);
+} clap_clap_converter_factory_t;
+
+#ifdef __cplusplus
+}
+#endif