Add a ModelPlugin that can be used to load and update models.

PiperOrigin-RevId: 861077626
Change-Id: I3ef4989cfbfff3632c5915c00ebda1e7a48716e8

src/experimental/platform/plugin.cc

@@ -36,10 +36,26 @@ void ForEachGuiPlugin(const std::function<void(GuiPlugin*)>& fn) {
   }
 }
 
+void RegisterModelPlugin(const ModelPlugin* plugin) {
+  if (plugin->name == nullptr || plugin->name[0] == '\0') {
+    mju_error("Plugin name must not be empty or null.");
+  }
+  GlobalTable<ModelPlugin>::GetSingleton().AppendIfUnique(*plugin);
+}
+
+void ForEachModelPlugin(const std::function<void(ModelPlugin*)>& fn) {
+  auto& table = GlobalTable<ModelPlugin>::GetSingleton();
+  for (int i = 0; i < table.count(); ++i) {
+    const ModelPlugin* plugin = table.GetAtSlot(i);
+    fn(const_cast<ModelPlugin*>(plugin));
+  }
+}
+
 }  // namespace mujoco::platform
 
 using mujoco::GlobalTable;
 using GuiPlugin = mujoco::platform::GuiPlugin;
+using ModelPlugin = mujoco::platform::ModelPlugin;
 
 template <>
 const char* GlobalTable<GuiPlugin>::HumanReadableTypeName() {
@@ -61,3 +77,24 @@ bool GlobalTable<GuiPlugin>::CopyObject(GuiPlugin& dst, const GuiPlugin& src, Er
   dst = src;
   return true;
 }
+
+template <>
+const char* GlobalTable<ModelPlugin>::HumanReadableTypeName() {
+  return "model plugin";
+}
+
+template <>
+std::string_view GlobalTable<ModelPlugin>::ObjectKey(const ModelPlugin& plugin) {
+  return std::string_view(plugin.name);
+}
+
+template <>
+bool GlobalTable<ModelPlugin>::ObjectEqual(const ModelPlugin& p1, const ModelPlugin& p2) {
+  return CaseInsensitiveEqual(p1.name, p2.name);
+}
+
+template <>
+bool GlobalTable<ModelPlugin>::CopyObject(ModelPlugin& dst, const ModelPlugin& src, ErrorMessage& err) {
+  dst = src;
+  return true;
+}

src/experimental/platform/plugin.h

@@ -16,6 +16,7 @@
 #define MUJOCO_SRC_EXPERIMENTAL_PLATFORM_PLUGIN_H_
 
 #include <functional>
+#include <mujoco/mujoco.h>
 
 namespace mujoco::platform {
 
@@ -46,6 +47,34 @@ struct GuiPlugin final {
   void* data = nullptr;
 };
 
+struct ModelPlugin final {
+  using GetModelToLoadFn = const char* (*)(ModelPlugin * self, int* size,
+                                           char* content_type,
+                                           int content_type_size,
+                                           char* model_name,
+                                           int model_name_size);
+  using PostModelLoadedFn = void (*)(ModelPlugin* self, const char* model_path);
+  using DoUpdateFn = bool (*)(ModelPlugin* self, mjModel* model, mjData* data);
+
+  // The name of the plugin; must be unique.
+  const char* name = "";
+
+  // Callback for when the plugin wants to load a new model. This function will
+  // return a buffer containing the model data as well as the content type of
+  // the buffer. Returns nullptr if no model needs to be loaded.s
+  GetModelToLoadFn get_model_to_load = nullptr;
+
+  // Callback when a new model is loaded.
+  PostModelLoadedFn post_model_loaded = nullptr;
+
+  // Callback when the physics simulation is updated. Returns true if the
+  // simulation should be stepped.
+  DoUpdateFn do_update = nullptr;
+
+  // Optional data pointer.
+  void* data = nullptr;
+};
+
 // Registers a plugin with a global registry. The plugin must have a
 // case-insensitive unique name.
 void RegisterGuiPlugin(const GuiPlugin* plugin);
@@ -53,6 +82,13 @@ void RegisterGuiPlugin(const GuiPlugin* plugin);
 // Executes the given function for each registered plugin.
 void ForEachGuiPlugin(const std::function<void(GuiPlugin*)>& fn);
 
+// Registers a plugin with a global registry. The plugin must have a
+// case-insensitive unique name.
+void RegisterModelPlugin(const ModelPlugin* plugin);
+
+// Executes the given function for each registered plugin.
+void ForEachModelPlugin(const std::function<void(ModelPlugin*)>& fn);
+
 }  // namespace mujoco::platform
 
 #endif  // MUJOCO_SRC_EXPERIMENTAL_PLATFORM_PLUGIN_H_