render implement thread, wrap GL commands into tasks

src/app.h

@@ -249,4 +249,69 @@ public:
     bool get_ui_rtl() const;
 
     void cmd_convert(std::string pano_path, std::string out_path);
+
+    bool is_render_thread()
+    {
+        extern std::thread::id render_thread_id;
+        extern std::thread::id gl_thread;
+        return std::this_thread::get_id() == render_thread_id || std::this_thread::get_id() == gl_thread;
+    }
+
+    // don't capture a reference to this ptr as the object may be destroyed
+    // by the time the task is executed
+    template<typename T, typename R = std::result_of<T()>::type>
+    std::future<R> render_task_async(T task)
+    {
+#ifdef _WIN32
+        extern std::deque<std::packaged_task<R()>> render_tasklist;
+        extern std::mutex render_task_mutex;
+        extern std::condition_variable render_cv;
+        std::packaged_task<R()> pt(task);
+        std::future<R> f = pt.get_future();
+        if (is_render_thread())
+        {
+            pt();
+        }
+        else
+        {
+            {
+                std::lock_guard<std::mutex> lock(render_task_mutex);
+                render_tasklist.push_back(std::move(pt));
+            }
+            render_cv.notify_all();
+        }
+        return f;
+#endif // _WIN32
+    }
+
+    template<typename T, typename R = std::result_of<T()>::type>
+    R render_task(T task)
+    {
+#ifdef _WIN32
+        extern std::deque<std::packaged_task<R()>> render_tasklist;
+        extern std::mutex render_task_mutex;
+        extern std::condition_variable render_cv;
+        std::packaged_task<R()> pt(task);
+        std::future<R> f = pt.get_future();
+        if (is_render_thread())
+        {
+            pt();
+        }
+        else
+        {
+            {
+                std::lock_guard<std::mutex> lock(render_task_mutex);
+                render_tasklist.push_back(std::move(pt));
+            }
+            render_cv.notify_all();
+        }
+        return f.get();
+#endif // _WIN32
+    }
+
+    void render_sync()
+    {
+        render_task([] {});
+    }
+
 };