diff --git a/src/Engine.cpp b/src/Engine.cpp
new file mode 100644
index 0000000..3469a33
--- /dev/null
+++ b/src/Engine.cpp
@@ -0,0 +1,114 @@
+#include "Engine.hpp"
+#include "gui/gui.hpp"
+
+namespace ougge {
+
+Engine::Engine()
+    : gameObjectPool(GAMEOBJECTPOOL_SIZE), textures(&resourceManager)
+{
+}
+
+void Engine::init(){
+    engineManagedAssembly = mono.loadAssembly("Ougge.dll");
+    gameObjectClass = engineManagedAssembly->getClass("Ougge", "GameObject");
+    gameObjectCtor = Mono::Method<void(u64, u32)>(gameObjectClass, ".ctor");
+    gameObjectInvokeUpdate = Mono::Method<void(f64)>(gameObjectClass, "InvokeUpdate");
+    gameObjectTryCreateComponent = Mono::Method<Mono::Bool(Mono::String)>(gameObjectClass, "TryCreateComponent_internal");
+}
+
+void Engine::openMainWindow(const std::string& window_title){
+    mainWindow.open(window_title, resourceManager);
+}
+
+void Engine::startLoop(){
+    if(loop_running)
+        throw UsefulException("loop is running already");
+    
+    nsec_t prev_update_time_ns = getMonotonicTimeNsec();
+    loop_running=true;
+    // main loop
+    while(loop_running){
+        mainWindow.pollEvents(&loop_running);
+        if(!loop_running)
+            break;
+        
+        nsec_t update_time_ns = getMonotonicTimeNsec();
+        if(update_time_ns < prev_update_time_ns)
+            throw UsefulException("monotonic clock returned unexpected value");
+        f64 delta_time_s = (f64)(update_time_ns - prev_update_time_ns) / 1e9;
+        prev_update_time_ns = update_time_ns;
+        
+        tryDrawFrame(delta_time_s);
+        
+        nsec_t after_update_time_ns = getMonotonicTimeNsec();
+        nsec_t frame_delay_ns = (nsec_t)1e9 / mainWindow.fps_max - (after_update_time_ns - update_time_ns);
+        if(frame_delay_ns > 0){
+            SDL_Delay(frame_delay_ns / 1e6);
+        }
+    }
+
+    mainWindow.close();
+}
+
+void Engine::stopLoop(){
+    loop_running = false;
+}
+
+void Engine::tryDrawFrame(f64 deltaTime){
+    static std::string error_message;
+    static bool draw_error_window = false;
+    try {
+        mainWindow.beginFrame();
+        
+        if(draw_error_window)
+            gui::drawErrorWindow(error_message, &draw_error_window);
+        else {
+            updateGameObjects(deltaTime);
+            if(!updateCallback.isNull())
+                updateCallback(deltaTime);
+        }
+        mainWindow.endFrame();
+    }
+    catch(const std::exception& e){
+        error_message = "Catched exception: " + std::string(e.what());
+        draw_error_window = true;
+        std::cerr<<error_message<<std::endl;
+    }
+    catch(const char* cstr){
+        error_message = "Catched error message (const char*): " + std::string(cstr);
+        draw_error_window = true;
+        std::cerr<<error_message<<std::endl;
+    }
+    catch(const std::string& str){
+        error_message = "Catched error message (std::string): " + str;
+        draw_error_window = true;
+        std::cerr<<error_message<<std::endl;
+    }
+    catch(...){
+        error_message = "Catched unknown error";
+        draw_error_window = true;
+        std::cerr<<error_message<<std::endl;
+    }
+}
+
+
+void Engine::updateGameObjects(f64 deltaTime){
+    for(auto pair : gameObjectPool){
+        gameObjectInvokeUpdate(pair.second.getObjectHandle().getObject(), deltaTime);
+    }
+}
+
+game::GameObject& Engine::createGameObject(){
+    auto pair = gameObjectPool.emplace(game::GameObject(mono.createObject(gameObjectClass)));
+    game::GameObject& obj = pair.second;
+    gameObjectCtor(obj.getObjectHandle().getObject(), ++obj_id, pair.first);
+    return obj;
+}
+
+bool Engine::tryCreateComponent(game::GameObject& obj, const std::string& componentClassName){
+    Mono::String componentClassNameManaged = mono.createString(componentClassName);
+    Mono::Bool created = gameObjectTryCreateComponent(obj.getObjectHandle().getObject(), componentClassNameManaged);
+    return created.wide_bool;
+}
+
+}
diff --git a/src/Engine.hpp b/src/Engine.hpp
new file mode 100644
index 0000000..d55609e
--- /dev/null
+++ b/src/Engine.hpp
@@ -0,0 +1,51 @@
+#pragma once
+
+#include "common/function_shared_ptr.hpp"
+#include "mono/mono.hpp"
+#include "game/GameObjectPool.hpp"
+#include "gui/MainWindow.hpp"
+#include "resources/textures.hpp"
+
+namespace ougge {
+
+#define GAMEOBJECTPOOL_SIZE 64*1024
+
+using UpdateFunc_t = function_shared_ptr<void(f64)>;
+
+class Engine {
+    bool loop_running = false;
+
+    game::GameObjectPool gameObjectPool;
+    u64 obj_id = 0;
+    MonoClass* gameObjectClass;
+    Mono::Method<void(u64, u32)> gameObjectCtor;
+    Mono::Method<void(f64)> gameObjectInvokeUpdate;
+    Mono::Method<Mono::Bool(Mono::String)> gameObjectTryCreateComponent;
+    
+public:
+    gui::MainWindow mainWindow;
+    UpdateFunc_t updateCallback;
+
+    Mono::RuntimeJIT mono;
+    std::shared_ptr<Mono::Assembly> engineManagedAssembly;
+
+    resources::ResourceManager resourceManager;
+    resources::CacheStorage<resources::Texture> textures;
+
+    Engine();
+    void init();
+    void openMainWindow(const std::string& window_title);
+    // start game loop on the current thread
+    void startLoop();
+    void stopLoop();
+
+    game::GameObject& createGameObject();
+    bool tryCreateComponent(game::GameObject& obj, const std::string& componentClassName);
+    
+
+private:
+    void tryDrawFrame(f64 deltaTime);
+    void updateGameObjects(f64 deltaTime);
+};
+
+}
diff --git a/src/common/UsefulException.cpp b/src/common/UsefulException.cpp
new file mode 100644
index 0000000..5e9e8ac
--- /dev/null
+++ b/src/common/UsefulException.cpp
@@ -0,0 +1,15 @@
+#include "UsefulException.hpp"
+#include <sstream>
+
+UsefulException_::UsefulException_(const std::string& _message, const std::string& _file, const std::string& _func, int _line_n)
+    : message(_message), file(_file), function(_func), line_n(_line_n)
+{
+    std::stringstream ss;
+    ss<<message<<'\n';
+    ss<<"    at "<<file<<':'<<_line_n<<" in "<<function;
+    complete_text = ss.str();
+}
+
+char const* UsefulException_::what() const noexcept {
+    return complete_text.c_str();
+}
diff --git a/src/common/UsefulException.hpp b/src/common/UsefulException.hpp
new file mode 100644
index 0000000..d925ae7
--- /dev/null
+++ b/src/common/UsefulException.hpp
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <stdexcept>
+#include <string>
+
+#define UsefulException(MSG) UsefulException_(MSG, __FILE__, __func__, __LINE__)
+
+class UsefulException_ : public std::exception {
+    std::string message;
+    std::string file;
+    std::string function;
+    int line_n;
+    std::string complete_text;
+
+public:
+    UsefulException_(const std::string& msg, const std::string& _file, const std::string& _func, int line_n);
+
+    virtual char const* what() const noexcept;
+};
+
+#define useful_assert(EXPR, ERRMSG) if(!(EXPR)) throw UsefulException(ERRMSG);
diff --git a/src/common/function_shared_ptr.hpp b/src/common/function_shared_ptr.hpp
new file mode 100644
index 0000000..ff7de84
--- /dev/null
+++ b/src/common/function_shared_ptr.hpp
@@ -0,0 +1,50 @@
+#pragma once
+
+#include <functional>
+#include <memory>
+#include "UsefulException.hpp"
+
+
+template<typename SignatureT> class function_shared_ptr;
+template<typename ReturnT, typename... ArgTypes>
+class function_shared_ptr<ReturnT(ArgTypes...)>
+{
+public:
+    using func_t = std::function<ReturnT(ArgTypes...)>;
+    using ptr_t = std::shared_ptr<func_t>;
+
+protected:
+    ptr_t func_ptr;
+
+public:
+    function_shared_ptr() = default;
+    function_shared_ptr(const function_shared_ptr&) = default;
+    function_shared_ptr(function_shared_ptr&&) = default;
+    function_shared_ptr(const ptr_t& p) : func_ptr(p) { }
+    function_shared_ptr(ptr_t&& p) : func_ptr(p) { }
+    template<typename FunctionT>
+    function_shared_ptr(FunctionT f){ func_ptr = std::make_shared<func_t>(f); }
+
+    function_shared_ptr& operator=(const function_shared_ptr&) = default;
+    function_shared_ptr& operator=(function_shared_ptr&&) = default;
+
+    bool isNull() const { return func_ptr == nullptr; }
+
+    //TODO: make inline
+
+    // ReturnT is not void
+    template<typename RT = ReturnT>
+    std::enable_if_t<!std::is_void<RT>::value, RT>  operator()(ArgTypes... args){
+        if(func_ptr == nullptr)
+            throw UsefulException("function_shared_ptr is null");
+        return func_ptr->operator()(args...);
+    }
+    
+    // ReturnT is void
+    template<typename RT = ReturnT>
+    std::enable_if_t<std::is_void<RT>::value, RT>  operator()(ArgTypes... args){
+        if(func_ptr == nullptr)
+            throw UsefulException("function_shared_ptr is null");
+        func_ptr->operator()(args...);
+    }
+};
diff --git a/src/common/math.hpp b/src/common/math.hpp
new file mode 100644
index 0000000..a0a7128
--- /dev/null
+++ b/src/common/math.hpp
@@ -0,0 +1,47 @@
+#pragma once
+
+#include "std.hpp"
+#include <cmath>
+
+#ifndef M_PI
+    #define M_E		2.7182818284590452354
+    #define M_LOG2E		1.4426950408889634074
+    #define M_LOG10E	0.43429448190325182765
+    #define M_LN2		0.69314718055994530942
+    #define M_LN10		2.30258509299404568402
+    #define M_PI		3.14159265358979323846
+    #define M_PI_2		1.57079632679489661923
+    #define M_PI_4		0.78539816339744830962
+    #define M_1_PI		0.31830988618379067154
+    #define M_2_PI		0.63661977236758134308
+    #define M_2_SQRTPI	1.12837916709551257390
+    #define M_SQRT2		1.41421356237309504880
+    #define M_SQRT1_2	0.70710678118654752440
+#endif
+
+struct Vec2 {
+    f32 x = 0, y = 0;
+};
+
+struct Vec3 {
+    f32 x = 0, y = 0, z = 0;
+};
+
+struct Vec4 {
+    f32 x = 0, y = 0, z = 0, w = 0;
+};
+
+/// radians
+typedef f32 angle_t;
+
+static inline angle_t normalizeAngle(angle_t a){
+    return std::fmodf(a + M_PI, 2*M_PI) - M_PI;
+}
+
+static inline f32 angleToDegree(angle_t a){
+    return (a / M_PI) * 180;
+}
+
+static inline angle_t degreeToRadian(f32 d){
+    return (d / 180) * M_PI;
+}
\ No newline at end of file
diff --git a/src/common/ougge_format.cpp b/src/common/ougge_format.cpp
new file mode 100644
index 0000000..f3f7642
--- /dev/null
+++ b/src/common/ougge_format.cpp
@@ -0,0 +1,84 @@
+#include <sstream>
+#include <stdarg.h>
+#include "ougge_format.hpp"
+#include "UsefulException.hpp"
+
+std::string _ougge_format(const std::string& format_str, const size_t args_count, ...){
+    va_list vl;
+    va_start(vl, args_count);
+    std::stringstream ss;
+    
+    for(size_t i = 0; i < format_str.length(); i++){
+        char c = format_str[i];
+
+        // format specifier
+        if(c == '%'){
+            c = format_str[++i];
+            bool l = false;
+            while(c == 'l'){
+                l = true;
+                c = format_str[++i];
+            }
+            
+            switch(c){
+                case 'u':
+                    if(l) ss<<(u64)va_arg(vl, u64);
+                    else ss<<(u32)va_arg(vl, u32);
+                    break;
+                case 'i':
+                case 'd':
+                    if(l) ss<<(i64)va_arg(vl, i64);
+                    else ss<<(i32)va_arg(vl, i32);
+                    break;
+                case 'f':
+                    // f32 is promoted to f64 when passed through '...'
+                    ss<<(f64)va_arg(vl, f64);
+                    break;
+                case 'p':
+                    ss<<(void*)va_arg(vl, void*);
+                    break;
+                case 'x':
+                    if(l) ss<<std::hex<<(u64)va_arg(vl, u64);
+                    else ss<<std::hex<<(u32)va_arg(vl, u32);
+                    break;
+                case 's': {
+                    const char* cptr = va_arg(vl,char*);
+                    if(cptr != nullptr)
+                        ss<<cptr;
+                    else ss<<"<nullptr>";
+                    break;
+                }
+                case 'c':
+                    ss<<(char)va_arg(vl,int);
+                    break;
+                default:
+                    throw UsefulException("invalid format cpecifier");
+            }
+        }
+
+        // regular character
+        else ss<<c;
+    }
+
+    va_end(vl);
+    return ss.str();
+}
+
+
+std::string formatSizeHumanReadable(std::size_t b){
+    std::stringstream ss;
+    ss.precision(3);
+    std::size_t k = b / 1024;
+    std::size_t m = k / 1024;
+    std::size_t g = m / 1024;
+    
+    if(g)
+        ss<<m / 1024.0f<<'G';
+    else if(m)
+        ss<<k / 1024.0f<<'M';
+    else if(k)
+        ss<<b / 1024.0f<<'K';
+    else ss<<b;
+
+    return ss.str();
+}
diff --git a/src/common/ougge_format.hpp b/src/common/ougge_format.hpp
new file mode 100644
index 0000000..64ce2ab
--- /dev/null
+++ b/src/common/ougge_format.hpp
@@ -0,0 +1,8 @@
+#pragma once
+
+#include "std.hpp"
+
+std::string _ougge_format(const std::string& format_str, const size_t args_count, ...);
+#define ougge_format(FORMAT_STR, ARGS...) _ougge_format(FORMAT_STR, count_args(ARGS) ,##ARGS)
+
+std::string formatSizeHumanReadable(std::size_t byte_n);
diff --git a/src/common/std.hpp b/src/common/std.hpp
new file mode 100644
index 0000000..bf7acb5
--- /dev/null
+++ b/src/common/std.hpp
@@ -0,0 +1,62 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <memory>
+
+typedef int8_t i8;
+typedef uint8_t u8;
+typedef int16_t i16;
+typedef uint16_t u16;
+typedef int32_t i32;
+typedef uint32_t u32;
+typedef int64_t i64;
+typedef uint64_t u64;
+typedef float f32;
+typedef double f64;
+/// anonymous pointer without specified freeMembers() func
+typedef void* Pointer;
+
+#define nameof(V) #V
+
+#ifdef _MSC_VER
+    #pragma comment(lib, "mincore_downlevel.lib") // Support OS older than SDK
+    #define _CRT_SECURE_NO_WARNINGS 1
+    #define EXPORT __declspec(dllexport)
+    #define CALL  __cdecl
+#elif defined(__GNUC__)
+    #define EXPORT __attribute__((visibility("default")))
+    #if __SIZEOF_POINTER__ == 4
+        #define CALL  __attribute__((__cdecl__))
+    #else
+        #define CALL
+    #endif
+    #ifndef typeof
+        #define typeof(X) __typeof__(X)
+    #endif
+#else
+    #pragma GCC error "unknown compiler"
+#endif
+
+#define __count_args( \
+    a0, a1, a2, a3, a4, a5, a6, a7 , \
+    a8, a9, a10,a11,a12,a13,a14,a15, \
+    a16,a17,a18,a19,a20,a21,a22,a23, \
+    a24,a25,a26,a27,a28,a29,a30,a31, \
+    a32,a33,a34,a35,a36,a37,a38,a39, \
+    a40,a41,a42,a43,a44,a45,a46,a47, \
+    a48,a49,a50,a51,a52,a53,a54,a55, \
+    a56,a57,a58,a59,a60,a61,a62,a63, \
+    a64,...) a64
+// Macro for counting variadic arguments (max 64)
+// (see usage in kprint.h)
+#define count_args(ARGS...) __count_args( \
+    ARGS, \
+    64,63,62,61,60,59,58,57, \
+    56,55,54,53,52,51,50,49, \
+    48,47,46,45,44,43,42,41, \
+    40,39,38,37,36,35,34,33, \
+    32,31,30,29,28,27,26,25, \
+    24,23,22,21,20,19,18,17, \
+    16,15,14,13,12,11,10,9, \
+    8, 7, 6, 5, 4, 3, 2, 1, 0)
diff --git a/src/common/time.cpp b/src/common/time.cpp
new file mode 100644
index 0000000..318b234
--- /dev/null
+++ b/src/common/time.cpp
@@ -0,0 +1,19 @@
+// posix version definition to use clock_gettime
+#ifndef _XOPEN_SOURCE 
+    #if __STDC_VERSION__ >= 199901L
+        #define _XOPEN_SOURCE 600
+    #else
+        #define _XOPEN_SOURCE 500
+    #endif
+#endif
+
+#include "time.hpp"
+#include <ctime>
+#include "UsefulException.hpp"
+
+nsec_t getMonotonicTimeNsec(){
+    struct timespec t;
+    if(clock_gettime(CLOCK_MONOTONIC, &t) != 0)
+        throw UsefulException("clock_gettime(CLOCK_MONOTONIC) error");
+    return (nsec_t)t.tv_sec * 1e9 + (nsec_t)t.tv_nsec;
+}
diff --git a/src/common/time.hpp b/src/common/time.hpp
new file mode 100644
index 0000000..70de9ab
--- /dev/null
+++ b/src/common/time.hpp
@@ -0,0 +1,20 @@
+#pragma once
+
+#include "std.hpp"
+
+/// nanoseconds
+typedef i64 nsec_t;
+
+/// can be used to measure delta time
+///@return time from some moment in nanoseconds.
+nsec_t getMonotonicTimeNsec();
+
+#define optime(N, LABEL, CODE) {\
+    nsec_t b = getMonotonicTimeNsec();\
+    for(u32 i = 0; i < (u32)N; i++) {\
+        CODE ;\
+    }\
+    nsec_t e = getMonotonicTimeNsec();\
+    nsec_t t = e-b;\
+    std::cout<<"operation '"<<LABEL<<"' took "<<t/1e6f<<" ms"<<std::endl;\
+}
diff --git a/src/game/GameObject.cpp b/src/game/GameObject.cpp
new file mode 100644
index 0000000..8d9dca4
--- /dev/null
+++ b/src/game/GameObject.cpp
@@ -0,0 +1,30 @@
+#include "GameObject.hpp"
+
+namespace ougge::game {
+
+std::ostream& operator<<(std::ostream& s, Transform& t){
+    s<<"{ position: {x: "<<t.position.x<<", y: "<<t.position.y;
+    s<<"}, rotation: "<<t.rotation;
+    s<<", scale {x: "<<t.scale.x<<", y: "<<t.scale.y<<"} }";
+    return s;
+}
+
+GameObject::GameObject(Mono::Object managed_obj)
+    : object_handle(managed_obj) 
+{}
+
+GameObject::GameObject(GameObject &&o) :
+    object_handle(std::move(o.object_handle)),
+    parent(o.parent),
+    transform(o.transform)
+{
+}
+
+GameObject& GameObject::operator=(GameObject &&o){
+    object_handle = std::move(o.object_handle);
+    parent = o.parent;
+    transform = o.transform;
+    return *this;
+}
+
+}
diff --git a/src/game/GameObject.hpp b/src/game/GameObject.hpp
new file mode 100644
index 0000000..7af9ff6
--- /dev/null
+++ b/src/game/GameObject.hpp
@@ -0,0 +1,45 @@
+#pragma once
+
+#include <map>
+#include <iostream>
+#include "../common/math.hpp"
+#include "../common/UsefulException.hpp"
+#include "../mono/mono.hpp"
+
+namespace ougge::game {
+
+class GameObject;
+
+struct Transform {
+    Vec2 scale = { 1, 1 };
+    Vec2 position = { 0, 0 };
+    angle_t rotation = 0;
+};
+
+std::ostream& operator<<(std::ostream& s, Transform& t);
+
+
+class GameObject {
+    Mono::ObjectHandle object_handle;
+    GameObject* parent;
+    Transform transform;
+
+public:
+    /// @warning Do not use this to create objects.
+    /// This constructor creates null values for GameObject arrays
+    /// GameObject* array = new GameObject[10];
+    /// array[0] = GameObject(initialized_mono_object_ptr)
+    GameObject() = default;
+    GameObject(Mono::Object managed_obj);
+    GameObject(const GameObject& o) = delete;
+    GameObject(GameObject&& o);
+    
+    GameObject& operator=(GameObject&& o);
+
+    inline Mono::ObjectHandle& getObjectHandle() { return object_handle; }
+    inline GameObject* getParent() { return parent; }
+    inline void setParent(GameObject* p) { parent = p; }
+    inline Transform& getTransform() { return transform; }
+};
+
+}
diff --git a/src/game/GameObjectPool.cpp b/src/game/GameObjectPool.cpp
new file mode 100644
index 0000000..5c25342
--- /dev/null
+++ b/src/game/GameObjectPool.cpp
@@ -0,0 +1,130 @@
+#include "GameObjectPool.hpp"
+#include <bit>
+#include <cstring>
+
+namespace ougge::game {
+
+GameObjectPool::GameObjectPool(u32 size)
+{
+    useful_assert(size % 64 == 0, "size of GameObjectPool must be a multiple of 64");
+    this->size = size; 
+    first_unused_index = 0;
+    buffer = new GameObject[size];
+    used_indices = new u64[size/64];
+    // std::memset(buffer, 0, size*sizeof(GameObject));
+    std::memset(used_indices, 0, size/8);
+}
+
+GameObjectPool::~GameObjectPool()
+{
+    delete[] buffer;
+    delete[] used_indices;
+}
+
+bool GameObjectPool::isIndexUsed(u32 index)
+{
+    return ( used_indices[index/64] & (u64(1)<<(index%64)) ) != 0;
+}
+
+u32 GameObjectPool::getNearestUnusedIndex(u32 startIndex)
+{
+    if(startIndex >= size)
+        return -1;
+    if(!isIndexUsed(startIndex))
+        return startIndex;
+    
+    u32 i = startIndex/64;
+    // mark previous bits as used
+    u64 u = used_indices[i] | ( (u64(1)<<startIndex%64) -1 );
+    while(u == u64(-1)){
+        i++;
+        if(i == size/64)
+            return -1;
+        u = used_indices[i];
+    }
+    u32 bitpos = std::countr_one(u);
+    if(bitpos == 64)
+        return -1;
+    u32 index = i*64 + bitpos;
+    return index;
+}
+
+u32 GameObjectPool::getNearestUsedIndex(u32 startIndex)
+{
+    if(startIndex >= size)
+        return -1;
+    if(isIndexUsed(startIndex))
+        return startIndex;
+    
+    u32 i = startIndex/64;
+    // mark previous bits as unused
+    u64 u = used_indices[i] & !( (u64(1)<<startIndex%64) -1 );
+    while(u == 0){
+        i++;
+        if(i == size/64)
+            return -1;
+        u = used_indices[i];
+    }
+    u32 bitpos = std::countr_zero(u);
+    if(bitpos == 64)
+        return -1;
+    u32 index = i*64 + bitpos;
+    return index;
+}
+
+GameObject& GameObjectPool::get(u32 index)
+{
+    if(index >= size)
+        throw UsefulException(ougge_format("index %i is out of size %i", index, size));
+    if(!isIndexUsed(index))
+        throw UsefulException(ougge_format("there is no object at index %i", index));
+    return buffer[index];
+}
+
+std::pair<u32, GameObject&> GameObjectPool::emplace(GameObject&& new_obj)
+{
+    u32 i = first_unused_index;
+    if(i == u32(-1))
+        throw UsefulException("can't put new GameObject to GameObjectPool because it's full");
+    
+    buffer[i] = std::move(new_obj);
+    GameObject& r = buffer[i];
+    used_indices[i/64] |= u64(1)<<(i%64); // mark index bit as used
+    first_unused_index = getNearestUnusedIndex(i+1);
+    return std::pair<u32, GameObject&>(i, r);
+}
+
+void GameObjectPool::erase(u32 index)
+{
+    if(index >= size)
+        throw UsefulException(ougge_format("index %i is out of size %i", index, size));
+    if(!isIndexUsed(index))
+        throw UsefulException(ougge_format("there is no object at index %i", index));
+    
+    buffer[index] = GameObject();
+    used_indices[index/64] &= ~(u64(1)<<(index%64)); // mark index bit as unused
+    if(index < first_unused_index)
+        first_unused_index = index;
+}
+
+GameObjectPool::iterator::iterator(GameObjectPool* pool, u32 index)
+    : pool(pool), index(index)
+{
+}
+
+std::pair<u32, GameObject&> GameObjectPool::iterator::operator*()
+{
+    if(index >= pool->size)
+        throw UsefulException("can't get value of end() iterator");
+    
+    GameObject& r = pool->buffer[index];
+    return  std::pair<u32, GameObject&>(index, r);
+}
+
+GameObjectPool::iterator& GameObjectPool::iterator::operator++()
+{
+    index = pool->getNearestUsedIndex(index+1);
+    return *this;
+}
+
+}
diff --git a/src/game/GameObjectPool.hpp b/src/game/GameObjectPool.hpp
new file mode 100644
index 0000000..8405915
--- /dev/null
+++ b/src/game/GameObjectPool.hpp
@@ -0,0 +1,70 @@
+#include "GameObject.hpp"
+
+namespace ougge::game {
+
+/*
+Fixed array that stores deleted elements indices as bits in array of u64.
+Fast emplace, erase and lookup. 
+
+------------------------[construct]------------------------
+operation 'GameObjectPool::GameObjectPool()' took 1.0549 ms
+operation 'other_collections_construct' took 0.0133 ms
+-------------------------[emplace]-------------------------
+operation 'GameObjectPool::emplace' took 8.0557 ms
+operation 'vector::emplace_back' took 11.3735 ms
+operation 'set::emplace' took 80.5633 ms
+operation 'list::emplace_front' took 18.1442 ms
+operation 'forward_list::emplace_front' took 11.5467 ms
+--------------------------[erase]--------------------------
+operation 'GameObjectPool::erase' took 0.2745 ms
+operation 'vector::erase' took 15790.6 ms
+operation 'set::erase' took 1.2697 ms
+operation 'list::erase_after' took 0.93 ms
+operation 'forward_list::erase_after' took 1.1127 ms
+-------------------------[iterate]-------------------------
+operation 'GameObjectPool::iterate' took 1.1166 ms
+operation 'vector::iterate' took 0.8883 ms
+operation 'set::iterate' took 2.8011 ms
+operation 'list::iterate' took 2.0766 ms
+operation 'forward_list::iterate' took 2.0823 ms
+*/
+
+class GameObjectPool {
+    GameObject* buffer;
+    u64* used_indices;
+    u32 size;
+    u32 first_unused_index;
+
+    bool isIndexUsed(u32 index);
+    u32 getNearestUnusedIndex(u32 startIndex);
+    u32 getNearestUsedIndex(u32 startIndex);
+public:
+
+    ///@param size must be a multiple of 64
+    GameObjectPool(u32 size);
+    ~GameObjectPool();
+    GameObject& get(u32 index);
+    std::pair<u32, GameObject&> emplace(GameObject&& new_obj);
+    void erase(u32 index);
+
+    #pragma region iterator class
+    class iterator {
+        GameObjectPool* pool;
+        u32 index = 0;
+    
+    public:
+        iterator(GameObjectPool* pool, u32 index);
+        std::pair<u32, GameObject&> operator*();
+        iterator& operator++();
+        inline bool operator!=(const iterator& o) const { return index != o.index; };
+        inline bool operator==(const iterator& o) const { return index == o.index; };
+    };
+    #pragma endregion
+
+    inline iterator begin() { return iterator(this, 0); }
+    inline iterator end() { return iterator(this, -1); }
+    
+    friend class iterator;
+};
+
+}
diff --git a/src/gui/ErrorWindow.cpp b/src/gui/ErrorWindow.cpp
new file mode 100644
index 0000000..597bbc8
--- /dev/null
+++ b/src/gui/ErrorWindow.cpp
@@ -0,0 +1,11 @@
+#include "gui.hpp"
+
+namespace ougge::gui {
+
+void drawErrorWindow(const std::string& msg, bool* draw_error_window){
+    ImGui::Begin("ERROR", draw_error_window);
+        ImGui::Text("%s", msg.c_str());
+    ImGui::End();
+}
+
+}
diff --git a/src/gui/MainWindow.cpp b/src/gui/MainWindow.cpp
new file mode 100644
index 0000000..d130517
--- /dev/null
+++ b/src/gui/MainWindow.cpp
@@ -0,0 +1,220 @@
+#include <backends/imgui_impl_sdl2.h>
+#include <backends/imgui_impl_sdlrenderer2.h>
+#include <iostream>
+#include "MainWindow.hpp"
+#include "gui_exceptions.hpp"
+#include "../common/ougge_format.hpp"
+#include "../common/math.hpp"
+
+namespace ougge::gui {
+
+f32 MainWindow::getDPI(){
+    i32 w=0, h=0;
+    SDL_GetRendererOutputSize(sdl_renderer, &w, &h);
+    i32 sim_w=0, sim_h=0;
+    SDL_GetWindowSize(sdl_window, &sim_w, &sim_h);
+    f32 wdpi=(f32)w / sim_w;
+    f32 hdpi=(f32)h / sim_h;
+    f32 dpi=SDL_sqrtf(wdpi*wdpi + hdpi*hdpi);
+    return dpi;
+}
+
+void MainWindow::open(const std::string& window_title, resources::ResourceManager& resourceManager){
+    SDL_TRY(SDL_Init(SDL_INIT_EVERYTHING));
+    SDL_version v;
+    SDL_GetVersion(&v);
+    std::cout<<ougge_format("SDL version: %u.%u.%u\n", v.major, v.minor, v.patch);
+    
+    // From 2.0.18: Enable native IME.
+#ifdef SDL_HINT_IME_SHOW_UI
+    SDL_SetHint(SDL_HINT_IME_SHOW_UI, "1");
+#endif
+    
+    SDL_WindowFlags window_flags = (SDL_WindowFlags)(
+        SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI
+    );
+    sdl_window = SDL_CreateWindow(window_title.c_str(),
+        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+        1280, 720, window_flags);
+    if(sdl_window == nullptr)
+        throw SDLException();
+    
+    SDL_RendererFlags renderer_flags = (SDL_RendererFlags)(
+        SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC
+    );
+    sdl_renderer = SDL_CreateRenderer(sdl_window, -1, renderer_flags);
+    if(sdl_renderer == nullptr)
+        throw SDLException();
+    
+    SDL_RendererInfo info;
+    SDL_GetRendererInfo(sdl_renderer, &info);
+    std::cout<<"Current SDL_Renderer driver: "<<info.name<<std::endl;
+
+    // Setup Dear ImGui context
+    IMGUI_CHECKVERSION();
+    ImGui::CreateContext();
+    ImGuiIO& io = ImGui::GetIO();
+    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard; // Enable Keyboard Controls   
+    io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;  // Enable Gamepad Controls
+    io.ConfigFlags |= ImGuiConfigFlags_DockingEnable;     // Enable Docking
+    io.ConfigDockingTransparentPayload = true;
+    io.ConfigInputTextCursorBlink = false;
+    // io.ConfigViewportsNoTaskBarIcon = true;
+    io.ConfigWindowsMoveFromTitleBarOnly = true;
+
+    // Setup Platform/Renderer backends
+    if(!ImGui_ImplSDL2_InitForSDLRenderer(sdl_window, sdl_renderer))
+        throw SDLException();
+    if(!ImGui_ImplSDLRenderer2_Init(sdl_renderer))
+        throw SDLException();
+
+    // Setup Dear ImGui style
+    ImGui::StyleColorsDark();
+    
+    resources::ResourceFactory* font_res = resourceManager.tryGetResource(default_font_path);
+    if(font_res == nullptr)
+        throw UsefulException("can't find default font resource");
+    f32 dpi = getDPI();
+    io.FontDefault = resources::ImFont_LoadFromResource(font_res, default_font_size, dpi);
+}
+
+void MainWindow::close(){
+    ImGui_ImplSDLRenderer2_Shutdown();
+    ImGui_ImplSDL2_Shutdown();
+    ImGui::DestroyContext();
+    SDL_DestroyRenderer(sdl_renderer);
+    SDL_DestroyWindow(sdl_window);
+    SDL_Quit();
+}
+
+void MainWindow::pollEvents(bool* loopRunning){
+    SDL_Event event;
+    while (SDL_PollEvent(&event)) {
+        ImGui_ImplSDL2_ProcessEvent(&event);
+        switch(event.type){
+            case SDL_QUIT: {
+                *loopRunning = false;
+                break;
+            }
+            case SDL_WINDOWEVENT: {
+                if(event.window.event == SDL_WINDOWEVENT_CLOSE 
+                    && event.window.windowID == SDL_GetWindowID(sdl_window))
+                {
+                    *loopRunning = false;
+                }
+                break;
+            }
+        }
+    }
+}
+
+
+void MainWindow::beginFrame(){
+    // Start the Dear ImGui frame
+    ImGui_ImplSDLRenderer2_NewFrame();
+    ImGui_ImplSDL2_NewFrame();
+    ImGui::NewFrame();
+
+    ImGuiIO& io = ImGui::GetIO();
+    SDL_RenderSetScale(sdl_renderer, io.DisplayFramebufferScale.x, io.DisplayFramebufferScale.y);
+    SDL_SetRenderDrawColor(sdl_renderer, 
+        (u8)(clear_color.x * 255),
+        (u8)(clear_color.y * 255),
+        (u8)(clear_color.z * 255),
+        (u8)(clear_color.w * 255));
+    SDL_RenderClear(sdl_renderer);
+
+    draw_bg_window();
+    draw_debug_window();
+}
+
+void MainWindow::endFrame(){
+    ImGui::Render();
+    ImGui_ImplSDLRenderer2_RenderDrawData(ImGui::GetDrawData(), sdl_renderer);
+    // Swap buffers
+    SDL_RenderPresent(sdl_renderer);
+}
+
+void MainWindow::draw_bg_window(){
+    const ImGuiDockNodeFlags dockspace_flags =
+            ImGuiDockNodeFlags_PassthruCentralNode;
+    const ImGuiWindowFlags window_flags =
+        ImGuiWindowFlags_MenuBar |
+        ImGuiWindowFlags_NoDocking |
+        ImGuiWindowFlags_NoScrollbar |
+        ImGuiWindowFlags_NoScrollWithMouse |
+        ImGuiWindowFlags_NoBringToFrontOnFocus |
+        ImGuiWindowFlags_NoFocusOnAppearing |
+        ImGuiWindowFlags_NoMove |
+        ImGuiWindowFlags_NoResize |
+        ImGuiWindowFlags_NoCollapse |
+        ImGuiWindowFlags_NoTitleBar |
+        ImGuiWindowFlags_NoBackground;
+    // not dockable window that always bound to viewport
+    ImGuiViewport* viewport = ImGui::GetWindowViewport();
+    ImGui::SetNextWindowPos(viewport->Pos, ImGuiCond_Always);
+    ImGui::SetNextWindowSize(viewport->Size, ImGuiCond_Always);
+    ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
+    ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
+	ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));
+    ImGui::Begin("bg_window", nullptr, window_flags);
+    ImGui::PopStyleVar(3);
+
+    // DockSpace
+    ImGuiID dockspace_id = ImGui::GetID("bg_dockspace");
+    ImGui::DockSpace(dockspace_id, ImVec2(0.0f, 0.0f), dockspace_flags);
+    
+    // MenuBar
+    if(ImGui::BeginMainMenuBar()){
+        if(ImGui::BeginMenu("test")){
+            if(ImGui::MenuItem("throw exception")){
+                ImGui::EndMenu();
+                ImGui::EndMainMenuBar();
+                ImGui::End();
+                throw UsefulException("example exception");
+            }
+            if(ImGui::MenuItem("throw const char*")){
+                ImGui::EndMenu();
+                ImGui::EndMainMenuBar();
+                ImGui::End();
+                throw "cptr";
+            }
+            if(ImGui::MenuItem("throw std::string")){
+                ImGui::EndMenu();
+                ImGui::EndMainMenuBar();
+                ImGui::End();
+                throw std::string("str");
+            }
+            if(ImGui::MenuItem("throw unknown")){
+                ImGui::EndMenu();
+                ImGui::EndMainMenuBar();
+                ImGui::End();
+                throw 111;
+            }
+            ImGui::EndMenu();
+        }
+        ImGui::EndMainMenuBar();
+    }
+
+    ImGui::End();
+}
+
+void MainWindow::draw_debug_window(){
+    ImGuiIO& io = ImGui::GetIO();
+    if(ImGui::Begin("Debug Options", &show_debug_window)){
+        ImGui::ColorEdit3("clear_color", (float*)&clear_color);
+        ImGui::InputInt("fps_max", &fps_max);
+        ImGui::Text("Application average %.3f ms/frame (%.2f FPS)", 1000.0f / io.Framerate, io.Framerate);
+        ImGui::Checkbox("Demo Window", &show_demo_window);
+        ImGui::Checkbox("Metrics/Debug Window", &show_metrics_window);
+        ImGui::End();
+    }
+
+    if (show_demo_window)
+        ImGui::ShowDemoWindow(&show_demo_window);
+
+    if (show_metrics_window)
+        ImGui::ShowMetricsWindow(&show_metrics_window);
+}
+
+}
\ No newline at end of file
diff --git a/src/gui/MainWindow.hpp b/src/gui/MainWindow.hpp
new file mode 100644
index 0000000..c2c7b67
--- /dev/null
+++ b/src/gui/MainWindow.hpp
@@ -0,0 +1,47 @@
+#pragma once
+
+#include <SDL.h>
+#include <imgui.h>
+#include "../common/std.hpp"
+#include "../common/time.hpp"
+#include "../resources/resources.hpp"
+#include "../resources/fonts.hpp"
+
+/// converts hex color to float vector
+#define RGBAHexToF(R8,G8,B8,A8) ImVec4(((u8)35)/255.0f, ((u8)35)/255.0f, ((u8)50)/255.0f, ((u8)255)/255.0f)
+/// converts float vector to hex color
+#define RGBAFToHex(VEC4) {(u8)(VEC4.x*255), (u8)(VEC4.y*255), (u8)(VEC4.z*255), (u8)(VEC4.w*255)}
+
+namespace ougge::gui {
+
+#define default_font_path "fonts/DroidSans.ttf"
+
+class MainWindow {
+public:
+    i32 fps_max = 60;
+    f32 default_font_size = 14.0f;
+    ImVec4 clear_color = RGBAHexToF(35,35,50,255);
+    SDL_Window* sdl_window = nullptr;
+    SDL_Renderer* sdl_renderer = nullptr;
+
+private:
+    bool show_debug_window = true;
+    bool show_demo_window = false;
+    bool show_metrics_window = false;
+
+public:
+    void open(const std::string& window_title, resources::ResourceManager& resourceManager);
+    void close();
+
+    /// process io events happened since previous frame
+    void pollEvents(bool* loopRunning);
+    void beginFrame();
+    void endFrame();
+
+    f32 getDPI();
+private:
+    void draw_debug_window();
+    void draw_bg_window();
+};
+
+}
diff --git a/src/gui/SceneView.hpp b/src/gui/SceneView.hpp
new file mode 100644
index 0000000..e69de29
diff --git a/src/gui/gui.hpp b/src/gui/gui.hpp
new file mode 100644
index 0000000..d626910
--- /dev/null
+++ b/src/gui/gui.hpp
@@ -0,0 +1,11 @@
+#pragma once
+
+#include <SDL.h>
+#include <imgui.h>
+#include "gui_exceptions.hpp"
+
+namespace ougge::gui {
+
+void drawErrorWindow(const std::string& msg, bool* draw_error_window);
+
+}
diff --git a/src/gui/gui_exceptions.cpp b/src/gui/gui_exceptions.cpp
new file mode 100644
index 0000000..2073b1e
--- /dev/null
+++ b/src/gui/gui_exceptions.cpp
@@ -0,0 +1,23 @@
+#include "gui_exceptions.hpp"
+#include <SDL.h>
+#include <SDL_image.h>
+
+namespace ougge::gui {
+
+SDLException_::SDLException_(const std::string& _file,const  std::string& _func, int _line_n)
+    : UsefulException_(std::string("SDLException: ") + SDL_GetError(), _file, _func, _line_n)
+{
+    SDL_ClearError();
+}
+
+#ifndef IMG_ClearError
+    #define IMG_ClearError SDL_ClearError
+#endif
+
+IMGException_::IMGException_(const std::string& _file,const  std::string& _func, int _line_n)
+    : UsefulException_(std::string("IMGException: ") + IMG_GetError(), _file, _func, _line_n)
+{
+    IMG_ClearError();
+}
+
+}
diff --git a/src/gui/gui_exceptions.hpp b/src/gui/gui_exceptions.hpp
new file mode 100644
index 0000000..90845ee
--- /dev/null
+++ b/src/gui/gui_exceptions.hpp
@@ -0,0 +1,27 @@
+#pragma once
+
+
+#include "../common/std.hpp"
+#include "../common/UsefulException.hpp"
+
+namespace ougge::gui {
+
+#define SDLException() SDLException_(__FILE__, __func__, __LINE__)
+
+class SDLException_ : public UsefulException_ {
+public:
+    SDLException_(const std::string& _file, const std::string& _func, int line_n);
+};
+
+
+#define IMGException() IMGException_(__FILE__, __func__, __LINE__)
+
+class IMGException_ : public UsefulException_ {
+public:
+    IMGException_(const std::string& _file, const std::string& _func, int line_n);
+};
+
+
+#define SDL_TRY(EXPR) if(EXPR) throw ::ougge::gui::SDLException();
+
+}
diff --git a/src/main.cpp b/src/main.cpp
new file mode 100644
index 0000000..cf5dd7d
--- /dev/null
+++ b/src/main.cpp
@@ -0,0 +1,65 @@
+#define SDL_MAIN_HANDLED
+#include <iostream>
+#include <iomanip>
+#include "common/UsefulException.hpp"
+#include "common/ougge_format.hpp"
+#include "Engine.hpp"
+#include "gui/gui.hpp"
+
+using namespace ougge;
+
+void drawTutel(Engine& engine){
+    resources::Texture* tutel = engine.textures.tryGetOrCreate("tutel.png", engine.mainWindow.sdl_renderer);
+    if(tutel == nullptr){
+        throw new UsefulException("couldn't find resource 'tutel.png'");
+    }
+    resources::SDL_RenderCopyExF_Params params;
+    params.target_section = SDL_FRectConstruct(100, 100, 400, 400);
+    static i32 si = 1;
+    params.rotation_angle = M_PI_4 * (si++ / engine.mainWindow.fps_max);
+    tutel->render(params);
+}
+
+int main(int argc, const char** argv){
+    try {
+        std::cout<<"initialized resource loader"<<std::endl;
+        
+        Engine engine;
+        std::cout<<"initialized mono jit runtime"<<std::endl;
+        engine.init();
+        std::cout<<"initialized game engine"<<std::endl;
+        
+        game::GameObject& exampleObj = engine.createGameObject();
+        std::string componentClassName = "Ougge.ExampleComponent";
+        if(!engine.tryCreateComponent(exampleObj, componentClassName))
+            throw UsefulException(ougge_format("couldn't create component '%s'", componentClassName.c_str()));
+        
+        std::cout<<"created ExampleObject"<<std::endl;
+        
+        engine.updateCallback = [&engine](f64 deltaTime) -> void {
+            drawTutel(engine);
+        };
+        
+        engine.openMainWindow("ougge");
+        std::cout<<"created sdl window"<<std::endl;
+        engine.startLoop();
+        std::cout<<"sdl window has been cosed"<<std::endl;
+    }
+    catch(const std::exception& e){
+        std::cerr<<"Catched exception: "<<e.what()<<std::endl;
+        return -1;
+    }
+    catch(const char* cstr){
+        std::cerr<<"Catched error message (const char*): "<<cstr<<std::endl;
+        return -1;
+    }
+    catch(const std::string& str){
+        std::cerr<<"Catched error message (std::string): "<<str<<std::endl;
+        return -1;
+    }
+    catch(...){
+        std::cerr<<"Catched unknown error"<<std::endl;
+        return -1;
+    }
+    return 0;
+}
diff --git a/src/mono/Assembly.cpp b/src/mono/Assembly.cpp
new file mode 100644
index 0000000..1a40dfa
--- /dev/null
+++ b/src/mono/Assembly.cpp
@@ -0,0 +1,17 @@
+#include "mono.hpp"
+
+namespace Mono {
+
+Assembly::Assembly(MonoAssembly *ptr)
+    : ptr(ptr), image(mono_assembly_get_image(ptr))
+{
+}
+
+MonoClass* Assembly::getClass(const std::string &name_space, const std::string &name){
+    auto c = mono_class_from_name(image, name_space.c_str(), name.c_str());
+    if(!c)
+        throw UsefulException(ougge_format("can't get class '%s.%s'", name_space.c_str(), name.c_str()));
+    return c;
+}
+
+}
diff --git a/src/mono/Runtime.cpp b/src/mono/Runtime.cpp
new file mode 100644
index 0000000..643f5f7
--- /dev/null
+++ b/src/mono/Runtime.cpp
@@ -0,0 +1,30 @@
+#include "mono.hpp"
+#include <mono/jit/jit.h>
+#include <mono/metadata/mono-config.h>
+#include <mono/metadata/appdomain.h>
+
+namespace Mono {
+
+RuntimeJIT::RuntimeJIT(const std::string& domain_name){
+    mono_set_dirs("mono-libs", "mono-libs");
+    mono_set_assemblies_path("mono-libs");
+    mono_config_parse("mono-libs/config.xml");
+
+    domain = mono_jit_init(domain_name.c_str());
+    if(!domain)
+        throw UsefulException("can't initialize mono domain");
+}
+
+RuntimeJIT::~RuntimeJIT(){
+    // TODO: fix segfault on cleanup
+    // mono_jit_cleanup(domain);
+}
+
+std::shared_ptr<Assembly> RuntimeJIT::loadAssembly(const std::string &name){
+    MonoAssembly* ptr = mono_domain_assembly_open(domain, name.c_str());
+    if(!ptr)
+        throw UsefulException(ougge_format("can't load assembly '%s'", name.c_str()));
+    return std::make_shared<Assembly>(ptr);
+}
+
+}
diff --git a/src/mono/mono.cpp b/src/mono/mono.cpp
new file mode 100644
index 0000000..c7fb99a
--- /dev/null
+++ b/src/mono/mono.cpp
@@ -0,0 +1,81 @@
+#include "mono.hpp"
+#include <mono/metadata/appdomain.h>
+
+namespace Mono {
+
+template <> MonoClass* getClass<SByte>(){ return mono_get_sbyte_class(); }
+template <> MonoClass* getClass<Byte>(){ return mono_get_byte_class(); }
+template <> MonoClass* getClass<Short>(){ return mono_get_int16_class(); }
+template <> MonoClass* getClass<UShort>(){ return mono_get_uint16_class(); }
+template <> MonoClass* getClass<Int>(){ return mono_get_int32_class(); }
+template <> MonoClass* getClass<UInt>(){ return mono_get_uint32_class(); }
+template <> MonoClass* getClass<Long>(){ return mono_get_int64_class(); }
+template <> MonoClass* getClass<ULong>(){ return mono_get_uint64_class(); }
+template <> MonoClass* getClass<Float>(){ return mono_get_single_class(); }
+template <> MonoClass* getClass<Double>(){ return mono_get_double_class(); }
+template <> MonoClass* getClass<Bool>(){ return mono_get_boolean_class(); }
+template <> MonoClass* getClass<Char>(){ return mono_get_char_class(); }
+template <> MonoClass* getClass<String>(){ return mono_get_string_class(); }
+template <> MonoClass* getClass<Object>(){ return mono_get_object_class(); }
+template <> MonoClass* getClass<Void>(){ return mono_get_void_class(); }
+
+
+void getMethodSignatureTypes(MonoMethod* mono_method,
+        MonoType** return_type,
+        std::vector<MonoType*>& argument_types)
+{
+    auto signature = mono_method_signature(mono_method);
+    void* iter = nullptr;
+    *return_type = mono_signature_get_return_type(signature);
+    MonoType* pt = nullptr;
+    while( (pt = mono_signature_get_params(signature, &iter)) ){
+        argument_types.push_back(pt);
+    }
+}
+
+MonoMethod* tryGetMonoMethod(MonoClass* target_class, const std::string& name,
+        MonoClass* return_class, MonoClass* arg_classes[], size_t arg_classes_size)
+{
+    if(target_class == nullptr)
+        throw UsefulException("target_class is nullptr");
+    
+    // iterate each method
+    void* iter = nullptr;
+    MonoMethod* m = nullptr;
+    std::vector<MonoType*> argument_types;
+    while( (m = mono_class_get_methods(target_class, &iter)) ){
+        // compare name
+        std::string m_name = mono_method_get_name(m);
+        if(m_name != name)
+            continue;
+        
+        argument_types.clear();
+        MonoType* return_type = nullptr;
+        getMethodSignatureTypes(m, &return_type, argument_types);
+        // compare argument count
+        if(argument_types.size() != arg_classes_size)
+            continue;
+        
+        // compare return type
+        if(!mono_metadata_type_equal(return_type, mono_class_get_type(return_class)))
+            continue;
+        
+        // compare argument types
+        bool argument_types_mismatch = false;
+        for(size_t i = 0; i < arg_classes_size; i++){
+            if(!mono_metadata_type_equal(argument_types[i], mono_class_get_type(arg_classes[i]))){
+                argument_types_mismatch = true;
+                break;
+            }
+        }
+        if(argument_types_mismatch)
+            continue;
+        
+        // passed all tests successfully
+        break;
+    }
+
+    return m;
+}
+
+}
diff --git a/src/mono/mono.hpp b/src/mono/mono.hpp
new file mode 100644
index 0000000..bffc10f
--- /dev/null
+++ b/src/mono/mono.hpp
@@ -0,0 +1,187 @@
+#pragma once
+
+#include "../common/std.hpp"
+#include "../common/UsefulException.hpp"
+#include "../common/ougge_format.hpp"
+#include <vector>
+#include <type_traits>
+#include <mono/metadata/class.h>
+#include <mono/metadata/assembly.h>
+#include <mono/metadata/object.h>
+
+namespace Mono {
+
+typedef i8 SByte;
+typedef u8 Byte;
+typedef i16 Short;
+typedef u16 UShort;
+typedef i32 Int;
+typedef u32 UInt;
+typedef i64 Long;
+typedef u64 ULong;
+typedef f32 Float;
+typedef f64 Double;
+typedef union { mono_bool wide_bool; } Bool; //USAGE: Bool t = {true};
+typedef char16_t Char;
+typedef MonoString* String;
+/// @warning MonoObject can be moved in memory by GC in any time and raw pointer will be invalid. 
+/// Use ObjectHandle where it is possible.
+typedef MonoObject* Object;
+typedef void Void;
+
+
+template<typename PrimitiveT>
+MonoClass* getClass(); 
+
+template<typename T>
+void* valueToVoidPtr(T& v){ return &v; }
+template<>
+inline void* valueToVoidPtr<Object>(Object& v){ return v; }
+template<>
+inline void* valueToVoidPtr<String>(String& v){ return v; }
+
+template<typename T>
+T valueFromMonoObject(MonoObject* o){
+    void* result_value_ptr = mono_object_unbox(o);
+    if(result_value_ptr == nullptr)
+        throw UsefulException("can't unbox method value");
+    return *((T*)result_value_ptr);
+}
+template<>
+inline Object valueFromMonoObject<Object>(MonoObject* o){ return o; }
+template<>
+inline String valueFromMonoObject<String>(MonoObject* o){ return (String)((void*)o); }
+
+void getMethodSignatureTypes(MonoMethod* mono_method,
+        MonoType** return_type,
+        std::vector<MonoType*>& argument_types);
+
+/// searches for method `name` in `target_class` with return type `return_class` and argument types `arg_classes`
+/// @return found method or nullptr
+MonoMethod* tryGetMonoMethod(MonoClass* target_class, const std::string& name,
+    MonoClass* return_class, MonoClass* arg_classes[], size_t arg_classes_size);
+
+
+template<typename SignatureT> class Method;
+template<typename ReturnT, typename... ArgTypes>
+class Method<ReturnT(ArgTypes...)>
+{
+    MonoMethod* method_ptr;
+
+public:
+    Method() { method_ptr = nullptr; }
+
+    /// all types must implement getClass<T>()
+    Method(MonoClass* target_class, const std::string& name){
+        static MonoClass* arg_classes[] { getClass<ArgTypes>()... };
+        static MonoClass* return_class { getClass<ReturnT>() };
+        method_ptr = tryGetMonoMethod(target_class, name, return_class, arg_classes, sizeof...(ArgTypes));
+        if(method_ptr == nullptr){
+            throw UsefulException(ougge_format("can't get method '%s' from class '%s'",
+                name.c_str(), mono_class_get_name(target_class)));
+        }
+    }
+
+    // ReturnT not is void
+    template<typename RT = ReturnT>
+    std::enable_if_t<!std::is_void<RT>::value, RT> operator()(MonoObject* class_instance, ArgTypes... args) const {
+        if(method_ptr == nullptr)
+            throw UsefulException("method_ptr is null");
+        
+        void* arg_array[] = { valueToVoidPtr(args)..., nullptr };
+        MonoObject* ex = nullptr;
+        MonoObject* result = mono_runtime_invoke(method_ptr, class_instance, arg_array, &ex);
+        if(ex){
+            //TODO:  call mono_trace_set_printerr_handler from  mono/mono/utils/mono-logger.h
+            mono_print_unhandled_exception(ex);
+            throw UsefulException("Some C# exception occured");
+        }
+        return valueFromMonoObject<ReturnT>(result);
+    };
+
+    // ReturnT is void
+    template<typename RT = ReturnT>
+    std::enable_if_t<std::is_void<RT>::value, RT> operator()(MonoObject* class_instance, ArgTypes... args) const {
+        if(method_ptr == nullptr)
+            throw UsefulException("method_ptr is null");
+        
+        void* arg_array[] = { valueToVoidPtr(args)..., nullptr };
+        MonoObject* ex = nullptr;
+        mono_runtime_invoke(method_ptr, class_instance, arg_array, &ex);
+        if(ex){
+            //TODO:  call mono_trace_set_printerr_handler from  mono/mono/utils/mono-logger.h
+            mono_print_unhandled_exception(ex);
+            throw UsefulException("Some C# exception occured");
+        }
+    };
+};
+
+
+class Assembly {
+    MonoAssembly* ptr;
+    MonoImage* image;
+
+public:
+    Assembly(MonoAssembly* ptr);
+    Assembly(const Assembly&) = delete;
+    
+    MonoClass* getClass(const std::string& name_space, const std::string& name);
+    MonoAssembly* getMonoAssembly() const { return ptr; }
+    MonoImage* getMonoImage() const { return image; }
+};
+
+
+///LINUX: `config.xml`, `mscorelib.dll`, `libmono-native.so` in `mono-libs` directory
+///
+///WINDOWS: `config.xml`, `mscorelib.dll` in `mono-libs` directory
+class RuntimeJIT {
+    MonoDomain* domain;
+public:
+    RuntimeJIT(const std::string& domain_name = "OuggeDomain");
+    RuntimeJIT(const RuntimeJIT&) = delete;
+    ~RuntimeJIT();
+    
+    inline MonoDomain* getDomain() { return domain; }
+    std::shared_ptr<Assembly> loadAssembly(const std::string& name);
+
+    inline Object createObject(MonoClass* klass) { return mono_object_new(domain, klass); }
+    inline String createString(const std::string& v) { return mono_string_new_len(domain, v.c_str(), v.size()); }
+    inline String createString(const char* v) { return mono_string_new(domain, v); }
+};
+
+/// @brief ObjectHandle can be used to store reliable reference to MonoObject.
+/// MonoObject can be moved in memory by GC in any time and raw pointer will be invalid. 
+struct ObjectHandle {
+    u32 gc_handle;
+
+    inline ObjectHandle() : gc_handle(0) {}
+
+    inline ObjectHandle(Object obj) {
+        gc_handle = mono_gchandle_new(obj, false);
+    }
+
+    /// implicitly create new ObjectHandle instead
+    inline ObjectHandle(const ObjectHandle& o) = delete;
+
+    inline ObjectHandle(ObjectHandle&& o) {
+        gc_handle = o.gc_handle;
+        o.gc_handle = 0;
+    }
+
+    inline ObjectHandle& operator=(ObjectHandle&& o) {
+        gc_handle = o.gc_handle;
+        o.gc_handle = 0;
+        return *this;
+    }
+
+    inline ~ObjectHandle() {
+        if(gc_handle)
+            mono_gchandle_free(gc_handle);
+    }
+
+    inline Object getObject() const {
+        return mono_gchandle_get_target(gc_handle);
+    }
+};
+
+}
diff --git a/src/resources/MemorySteam.cpp b/src/resources/MemorySteam.cpp
new file mode 100644
index 0000000..fea56e5
--- /dev/null
+++ b/src/resources/MemorySteam.cpp
@@ -0,0 +1,40 @@
+#include "MemoryStream.hpp"
+
+class MemoryStreamBuf : public std::streambuf {
+public:
+    MemoryStreamBuf(void* p, const std::size_t n);
+
+    virtual std::istream::pos_type seekoff(
+        std::istream::off_type off,
+        std::ios_base::seekdir dir,
+        std::ios_base::openmode which);
+};
+
+MemoryStreamBuf::MemoryStreamBuf(void* _p, const std::size_t n){
+    char* p=(char*)_p;
+    setg(p, p, p + n);
+    setp(p, p + n);
+}
+
+std::istream::pos_type MemoryStreamBuf::seekoff(
+    std::istream::off_type off,
+    std::ios_base::seekdir dir,
+    std::ios_base::openmode which)
+{
+    if (dir == std::ios_base::cur)
+        gbump(off);
+    else if (dir == std::ios_base::end)
+        setg(eback(), egptr() + off, egptr());
+    else if (dir == std::ios_base::beg)
+        setg(eback(), eback() + off, egptr());
+    return gptr() - eback();
+}
+
+
+MemoryStreamRead::MemoryStreamRead(const void* p, const std::size_t n)
+    : std::istream(new MemoryStreamBuf((void*)p, n))
+{}
+
+MemoryStreamRead::~MemoryStreamRead(){
+    delete rdbuf();
+}
diff --git a/src/resources/MemoryStream.hpp b/src/resources/MemoryStream.hpp
new file mode 100644
index 0000000..0f1ced9
--- /dev/null
+++ b/src/resources/MemoryStream.hpp
@@ -0,0 +1,8 @@
+#include <iostream>
+
+class MemoryStreamRead : public std::istream {
+public:
+    MemoryStreamRead(const void* p, const std::size_t n);
+
+    virtual ~MemoryStreamRead();
+};
\ No newline at end of file
diff --git a/src/resources/embedded_resources.h b/src/resources/embedded_resources.h
new file mode 100644
index 0000000..96333b1
--- /dev/null
+++ b/src/resources/embedded_resources.h
@@ -0,0 +1,64 @@
+////////////////////////////////////////////////////////////////
+//        This file was generated by resource_embedder        //
+//  https://timerix.ddns.net:3322/Timerix/resource_embedder   //
+////////////////////////////////////////////////////////////////
+//                          USAGE:                            //
+//    Put it in a SOURCE file to define variables             //
+//  #define EMBEDDED_RESOURCE_DEFINITION                      //
+//  #define EMBEDDED_RESOURCE_POSTFIX your_postfix            //
+//  #include "../../src/Resources/embedded_resources.h"       //
+//                                                            //
+//    Put it in a HEADER file to declare external variables   //
+//  #define EMBEDDED_RESOURCE_POSTFIX your_postfix            //
+//  #include "../../src/Resources/embedded_resources.h"       //
+//                                                            //
+//    Then you can access embedded files through              //
+//  EmbeddedResource_table_your_postfix. You can get table    //
+//  content by index and put it into a hashtable or a map.    //
+////////////////////////////////////////////////////////////////
+
+#pragma once
+#if __cplusplus
+extern "C" {
+#endif
+
+#include <stdint.h>
+#include <stddef.h>
+
+typedef struct {
+    const char* path;
+    const char* data;
+    size_t size;
+} EmbeddedResource;
+
+#define RSCAT(A,B,C...) A##B##C
+#ifdef EMBEDDED_RESOURCE_POSTFIX
+    #define _EmbeddedResource_table(P) \
+        RSCAT(EmbeddedResource_table_, P)
+    #define _EmbeddedResource_table_count(P) \
+        RSCAT(EmbeddedResource_table_, P, _count)
+#else
+    #define _EmbeddedResource_table(P) \
+        EmbeddedResource_table
+    #define _EmbeddedResource_table_count(P) \
+        EmbeddedResource_table_count
+#endif
+extern const EmbeddedResource _EmbeddedResource_table(EMBEDDED_RESOURCE_POSTFIX)[];
+extern const int _EmbeddedResource_table_count(EMBEDDED_RESOURCE_POSTFIX);
+
+#ifdef EMBEDDED_RESOURCE_DEFINITION
+const EmbeddedResource _EmbeddedResource_table(EMBEDDED_RESOURCE_POSTFIX)[]={
+
+};
+
+const int _EmbeddedResource_table_count(EMBEDDED_RESOURCE_POSTFIX)=0;
+#endif // EMBEDDED_RESOURCE_DEFINITION
+
+#undef _EmbeddedResource_table
+#undef _EmbeddedResource_table_count
+#undef EMBEDDED_RESOURCE_POSTFIX
+#undef RSCAT
+
+#if __cplusplus
+}
+#endif
diff --git a/src/resources/fonts.cpp b/src/resources/fonts.cpp
new file mode 100644
index 0000000..96cde0f
--- /dev/null
+++ b/src/resources/fonts.cpp
@@ -0,0 +1,29 @@
+#include "fonts.hpp"
+
+namespace ougge::resources {
+
+// select all glyphs from font
+static const ImWchar glyph_ranges[] = {
+    0x0020, 0xFFFF, 0
+};
+
+ImFont* ImFont_LoadFromFile(const std::string& file_path, f32 font_size, f32 dpi){
+    ImGuiIO& io = ImGui::GetIO();
+    font_size *= dpi;
+    return io.Fonts->AddFontFromFileTTF(file_path.c_str(), font_size, nullptr, glyph_ranges);
+}
+
+ImFont* ImFont_LoadFromResource(ResourceFactory* res, f32 font_size, f32 dpi){
+    ImGuiIO& io = ImGui::GetIO();
+    font_size *= dpi;
+    ImFontConfig font_cfg = ImFontConfig();
+    std::sprintf(font_cfg.Name, "%s %ipx", res->path.c_str(), (i32)font_size);
+    
+    char* font_data = new char[res->size]; 
+    res->openStream()->read(font_data, res->size);
+
+    return io.Fonts->AddFontFromMemoryTTF((void*)(font_data), res->size,
+        font_size, &font_cfg, glyph_ranges);
+}
+
+}
diff --git a/src/resources/fonts.hpp b/src/resources/fonts.hpp
new file mode 100644
index 0000000..6ab1b08
--- /dev/null
+++ b/src/resources/fonts.hpp
@@ -0,0 +1,13 @@
+#pragma once
+
+#include <imgui.h>
+#include "../common/std.hpp"
+#include "resources.hpp"
+
+namespace ougge::resources {
+
+ImFont* ImFont_LoadFromFile(const std::string& file_path, f32 font_size, f32 dpi);
+
+ImFont* ImFont_LoadFromResource(ResourceFactory* res, f32 font_size, f32 dpi);
+
+}
diff --git a/src/resources/resources.cpp b/src/resources/resources.cpp
new file mode 100644
index 0000000..5591582
--- /dev/null
+++ b/src/resources/resources.cpp
@@ -0,0 +1,64 @@
+#include <fstream>
+#include <sstream>
+#include "../common/UsefulException.hpp"
+#include "../common/ougge_format.hpp"
+#include "resources.hpp"
+#include "embedded_resources.h"
+#include "MemoryStream.hpp"
+
+namespace ougge::resources {
+
+ResourceFactory::ResourceFactory(const std::string& path, const std::size_t size, StreamFactoryMethod open_read_steam_func)
+  : path(path), size(size), openStream(open_read_steam_func)
+{}
+
+
+std::shared_ptr<ResourceMap> ResourceManager::_embeddedResourcesMap;
+
+void ResourceManager::loadEmbeddedResources(){
+    if(_embeddedResourcesMap != nullptr)
+        return;
+
+    _embeddedResourcesMap = std::make_shared<ResourceMap>();
+    for(int i = 0; i < EmbeddedResource_table_count; i++){
+        const EmbeddedResource& e = EmbeddedResource_table[i];
+        std::cout <<"loading resource '" << e.path << "' " 
+            << formatSizeHumanReadable(e.size) << std::endl;
+        
+        auto embedded_resource_factory = [e]() -> std::unique_ptr<std::istream> { 
+            return std::make_unique<MemoryStreamRead>(e.data, e.size); 
+        };
+
+        auto r = _embeddedResourcesMap->emplace(e.path, 
+            ResourceFactory(e.path, e.size, embedded_resource_factory));
+        if(!r.second)
+            throw UsefulException(ougge_format("can't load duplicate resource '%s'", e.path));
+    }
+    
+    _resourceMaps.push_back(_embeddedResourcesMap);
+}
+
+ResourceManager::ResourceManager(){
+    loadEmbeddedResources();
+}
+
+ResourceFactory* ResourceManager::tryGetResource(const std::string& path){
+    // reverse iteration of linked list
+    auto map_list_iterator = _resourceMaps.end();
+    while(map_list_iterator != _resourceMaps.begin()){
+        --map_list_iterator;
+        auto map = *map_list_iterator;
+
+        auto resource_iterator = map->find(path);
+        
+        // resource not found
+        if(resource_iterator == map->end())
+            return nullptr;
+        
+        return &resource_iterator->second;
+    }
+
+    return nullptr;
+}
+
+}
diff --git a/src/resources/resources.hpp b/src/resources/resources.hpp
new file mode 100644
index 0000000..2e6d8e6
--- /dev/null
+++ b/src/resources/resources.hpp
@@ -0,0 +1,74 @@
+#pragma once
+
+#include "../common/std.hpp"
+#include <iostream>
+#include <functional>
+#include <unordered_map>
+#include <memory>
+#include <list>
+
+namespace ougge::resources {
+
+class ResourceFactory {
+public:
+    const std::string path;
+    const std::size_t size;
+
+    using StreamFactoryMethod = std::function< std::unique_ptr<std::istream> () >;
+
+    ResourceFactory(const std::string& path, const std::size_t size, StreamFactoryMethod open_read_steam_func);
+
+    const StreamFactoryMethod openStream;
+};
+
+using ResourceMap = std::unordered_map<std::string, ResourceFactory>;
+
+class ResourceManager {
+    std::list<std::shared_ptr<ResourceMap>> _resourceMaps;
+    static std::shared_ptr<ResourceMap> _embeddedResourcesMap;
+    void loadEmbeddedResources();
+
+public:
+    ResourceManager();
+
+    void addResourceMap(std::shared_ptr<ResourceMap> m);
+    
+    std::shared_ptr<ResourceMap> loadResouceMap();
+    void removeResourceMap();
+
+    ResourceFactory* tryGetResource(const std::string& path);
+};
+
+/// @brief stores requested resources in memory
+/// @tparam T must implement constructor `T(ResourceFactory*, ...)`
+template<class T>
+class CacheStorage {
+    std::unordered_map<std::string, T> _map;
+    ResourceManager* _resourceManager;
+
+public:
+    CacheStorage(ResourceManager*);
+    CacheStorage(CacheStorage&&) = delete;
+    CacheStorage(const CacheStorage&) = delete;
+
+    template<typename... TCtorArgs>
+    T* tryGetOrCreate(const std::string& name, TCtorArgs&&... ctor_args){
+        auto it = _map.find(name);
+        if(it != _map.end())
+            return &it->second;
+        
+        ResourceFactory* res = _resourceManager->tryGetResource(name);
+        if(res == nullptr)
+            return nullptr;
+        
+        auto e = _map.emplace(name, T(res, ctor_args...));
+        return &e.first->second;
+    }
+};
+
+
+template <class T> inline CacheStorage<T>::CacheStorage(ResourceManager* resourceManager)
+    : _resourceManager(resourceManager)
+{}
+
+}
diff --git a/src/resources/textures.cpp b/src/resources/textures.cpp
new file mode 100644
index 0000000..ec6b672
--- /dev/null
+++ b/src/resources/textures.cpp
@@ -0,0 +1,96 @@
+#include "textures.hpp"
+#include <SDL_image.h>
+#include "../gui/gui_exceptions.hpp"
+
+namespace ougge::resources {
+
+Texture::Texture(ResourceFactory* r, SDL_Renderer* renderer) 
+    : Texture(*r->openStream(), r->size, renderer)
+{}
+
+Texture::Texture(std::istream& s, size_t size, SDL_Renderer* renderer)
+    : renderer(renderer), texture(nullptr), w(0), h(0)
+{
+    SDL_RWops* sdl_stream = SDL_RWFromIStream(s, size);
+    if(!sdl_stream)
+        throw gui::SDLException();
+    texture = std::shared_ptr<SDL_Texture>(IMG_LoadTexture_RW(renderer, sdl_stream, 1), SDL_DestroyTexture);
+    if(!texture)
+        throw gui::IMGException();
+    SDL_TRY(SDL_QueryTexture(texture.get(), nullptr, nullptr, &w, &h));
+}
+
+SDL_RenderCopyExF_Params::SDL_RenderCopyExF_Params()
+    : rotation_angle(0), flip(SDL_FLIP_NONE) 
+{}
+
+void Texture::render(const SDL_FRect& target_section){
+    SDL_TRY(
+        SDL_RenderCopyF(renderer, texture.get(), nullptr, &target_section)
+    );
+}
+
+void Texture::render(const SDL_FRect& target_section, const SDL_Rect& texture_section){
+    SDL_TRY(
+        SDL_RenderCopyF(renderer, texture.get(), &texture_section, &target_section)
+    );
+}
+
+void Texture::render(const SDL_RenderCopyExF_Params& p){
+    SDL_TRY(
+            SDL_RenderCopyExF(renderer, texture.get(),
+            optional_value_ptr_or_null(p.texture_section),
+            optional_value_ptr_or_null(p.target_section),
+            -1.0f * angleToDegree(normalizeAngle(p.rotation_angle)),
+            optional_value_ptr_or_null(p.rotation_center),
+            p.flip
+        )
+    )
+}
+
+static Sint64 istream_size(SDL_RWops* context){
+    return (Sint64)(size_t)context->hidden.unknown.data2;
+}
+
+static Sint64 istream_seek(SDL_RWops* context, Sint64 offset, i32 whence){
+    std::istream* stream = (std::istream*)context->hidden.unknown.data1;
+    switch(whence){
+        case SEEK_SET: stream->seekg(offset, std::ios::beg); break;
+        case SEEK_CUR: stream->seekg(offset, std::ios::cur); break;
+        case SEEK_END: stream->seekg(offset, std::ios::end); break;
+        default: break;
+    }
+    return stream->fail() ? -1 : (Sint64)stream->tellg();
+}
+
+static size_t istream_read(SDL_RWops* context, void *ptr, size_t size, size_t maxnum){
+    if(size == 0)
+        return -1;
+    std::istream* stream = (std::istream*)context->hidden.unknown.data1;
+    stream->read((char*)ptr, size * maxnum);
+
+    return stream->bad() ? -1 : stream->gcount() / size;
+}
+
+static i32 istream_close(SDL_RWops* context){
+    if (context)
+        SDL_FreeRW(context);
+    return 0;
+}
+
+SDL_RWops* SDL_RWFromIStream(std::istream& stream, size_t size){
+    SDL_RWops* rwops = SDL_AllocRW();
+    if(rwops) {
+        rwops->size = istream_size;
+        rwops->seek = istream_seek;
+        rwops->read = istream_read;
+        rwops->write = nullptr;
+        rwops->close = istream_close;
+        rwops->hidden.unknown.data1 = &stream;
+        rwops->hidden.unknown.data2 = (void*)size;
+        rwops->type = SDL_RWOPS_UNKNOWN;
+    }
+    return rwops;
+}
+
+}
diff --git a/src/resources/textures.hpp b/src/resources/textures.hpp
new file mode 100644
index 0000000..4869f77
--- /dev/null
+++ b/src/resources/textures.hpp
@@ -0,0 +1,44 @@
+#pragma once
+
+#include <iostream>
+#include <optional>
+#include <SDL.h>
+#include "resources.hpp"
+#include "../common/math.hpp"
+
+namespace ougge::resources {
+
+#define SDL_RectConstruct(X, Y, W, H) (SDL_Rect){X, Y, W, H}
+#define SDL_FRectConstruct(X, Y, W, H) (SDL_FRect){X, Y, W, H}
+#define SDL_PointConstruct(X, Y) (SDL_Point){X, Y, W, H}
+#define SDL_FPointConstruct(X, Y) (SDL_FPoint){X, Y, W, H}
+
+#define optional_value_ptr_or_null(OPT) (OPT ? &(*OPT) : nullptr)
+
+SDL_RWops* SDL_RWFromIStream(std::istream& stream, size_t size);
+
+struct SDL_RenderCopyExF_Params {
+    std::optional<SDL_Rect> texture_section;
+    std::optional<SDL_FRect> target_section;
+    std::optional<SDL_FPoint> rotation_center;
+    angle_t rotation_angle;
+    SDL_RendererFlip flip;
+    
+    SDL_RenderCopyExF_Params();
+};
+
+struct Texture {
+    SDL_Renderer* renderer;
+    std::shared_ptr<SDL_Texture> texture;
+    i32 w;
+    i32 h;
+
+    Texture(ResourceFactory* r, SDL_Renderer* renderer);
+    Texture(std::istream& s, size_t size, SDL_Renderer* renderer);
+
+    void render(const SDL_FRect& target_section);
+    void render(const SDL_FRect& target_section, const SDL_Rect& texture_section);
+    void render(const SDL_RenderCopyExF_Params& params);
+};
+
+}