initial work to re-implement FFI with background thread render loop

ios/src/PolyvoxFilamentFFIApi.cpp

@@ -0,0 +1,119 @@
+#include "ResourceBuffer.hpp"
+
+#include "FilamentViewer.hpp"
+#include "filament/LightManager.h"
+#include "Log.hpp"
+#include "ThreadPool.hpp"
+
+#include <thread>
+#include <functional>
+
+using namespace polyvox;
+
+#define FLUTTER_PLUGIN_EXPORT __attribute__((visibility("default")))
+
+class RenderLoop {
+public:
+    explicit RenderLoop() { 
+        _t = new std::thread([this]() {
+			while(!_stop) {
+				std::function<void()> task;
+				{
+					std::unique_lock<std::mutex> lock(_access);
+					if(_tasks.empty()) {
+						_cond.wait_for(lock, std::chrono::duration<int, std::milli>(5));
+						continue;
+					}
+					task = std::move(_tasks.front());
+					_tasks.pop_front();
+                    std::this_thread::sleep_for(
+                        std::chrono::milliseconds(_frameIntervalInMilliseconds));
+                }
+
+				task();
+			}
+		});
+	}
+	~RenderLoop() {
+		_stop = true;
+        _t->join();
+	}
+
+    void setRendering(bool rendering) {
+        _rendering = rendering;
+    }
+
+	template<class Rt>
+	auto add_task(std::packaged_task<Rt()>& pt) -> std::future<Rt> {
+		std::unique_lock<std::mutex> lock(_access);
+		auto ret = pt.get_future();
+		_tasks.push_back([pt=std::make_shared<std::packaged_task<Rt()>>(std::move(pt))]{ (*pt)();});
+		_cond.notify_one();
+		return ret;
+	}
+private: 
+    bool _stop = false;
+    bool _rendering = false;
+    int _frameIntervalInMilliseconds = 1000 / 60;
+	std::mutex _access;
+    FilamentViewer* _viewer = nullptr;
+    std::thread* _t = nullptr;
+	std::condition_variable _cond;
+	std::deque<std::function<void()>> _tasks;
+
+};
+
+
+
+extern "C" {
+
+  #include "PolyvoxFilamentApi.h"
+
+  static RenderLoop* _rl;
+
+  FLUTTER_PLUGIN_EXPORT const void* create_filament_viewer_ffi(const void* context, const ResourceLoaderWrapper* const loader) {
+    if(!_rl) {
+        _rl = new RenderLoop();
+    }
+    std::packaged_task<const void*()> lambda([&]() mutable  {
+        return (const void*) new FilamentViewer(context, loader);
+    });
+    auto fut = _rl->add_task(lambda);
+    fut.wait();
+    return fut.get();
+  }
+
+  FLUTTER_PLUGIN_EXPORT void update_viewport_and_camera_projection_ffi(void* const viewer, const uint32_t width, const uint32_t height, const float scaleFactor);
+    std::packaged_task<void()> lambda([&]() mutable  {
+        update_viewport_and_camera_projection(viewer, width, height, scaleFactor);
+    });
+    auto fut = _rl->add_task(lambda);
+    fut.wait();
+  }
+  
+
+  FLUTTER_PLUGIN_EXPORT bool set_rendering(bool rendering) {
+      if(!_rl) {
+        return false;
+      }
+      _rl->setRendering(rendering);
+      return true;
+  }
+
+  FLUTTER_PLUGIN_EXPORT void render_ffi(void* const viewer) {
+    std::packaged_task<void()> lambda([&]() mutable  {
+        render(viewer, 0);
+    });
+    auto fut = _rl->add_task(lambda);
+    fut.wait();
+  }
+
+  FLUTTER_PLUGIN_EXPORT void set_background_color_ffi(const void* const viewer, const float r, const float g, const float b, const float a) {
+    std::packaged_task<void()> lambda([&]() mutable  {
+        set_background_color(viewer, r, g,b, a);
+    });
+    auto fut = _rl->add_task(lambda);
+    fut.wait();
+  }
+
+}