diff --git a/src/GUI/MainWindow.cpp b/src/GUI/MainWindow.cpp
new file mode 100644
index 0000000..ea6125f
--- /dev/null
+++ b/src/GUI/MainWindow.cpp
@@ -0,0 +1,315 @@
+#include "MainWindow.hpp"
+#include "backends/imgui_impl_sdl2.h"
+#include "backends/imgui_impl_opengl3.h"
+
+namespace ougge::GUI {
+
+f32 MainWindow::getDPI(){
+    int w=0, h=0;
+    SDL_GL_GetDrawableSize(sdl_window, &w, &h);
+    int 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::init(const char* window_title){
+    SDL_TRY(SDL_Init(SDL_INIT_VIDEO));
+    SDL_version v;
+    SDL_GetVersion(&v);
+    std::cout<<format("SDL version: %u.%u.%u\n", v.major, v.minor, v.patch);
+    // GL 3.0 + GLSL 130
+    const char* glsl_version = "#version 130";
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0));
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE));
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3));
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 0));
+
+    // From 2.0.18: Enable native IME.
+#ifdef SDL_HINT_IME_SHOW_UI
+    SDL_SetHint(SDL_HINT_IME_SHOW_UI, "1");
+#endif
+    
+    // Create window with graphics context
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1));
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24));
+    SDL_TRY( SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8));
+    SDL_WindowFlags window_flags = (SDL_WindowFlags)(
+        SDL_WINDOW_OPENGL |
+        SDL_WINDOW_RESIZABLE |
+        SDL_WINDOW_ALLOW_HIGHDPI);
+    sdl_window = SDL_CreateWindow(window_title,
+        SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+        1280, 720, window_flags);
+    if(sdl_window == nullptr)
+        throw SDLException();
+    gl_context = SDL_GL_CreateContext(sdl_window);
+    if(gl_context == nullptr)
+        throw SDLException();
+    SDL_TRY( SDL_GL_MakeCurrent(sdl_window, gl_context));
+    SDL_TRY( SDL_GL_SetSwapInterval(1)); // Enable vsync
+
+    // 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_InitForOpenGL(sdl_window, gl_context) != true)
+        throw SDLException();
+    if(ImGui_ImplOpenGL3_Init(glsl_version) != true)
+        throw SDLException();
+
+    // Setup Dear ImGui style
+    ImGui::StyleColorsDark();
+}
+
+// Wait, poll and handle events (inputs, window resize, etc.)
+void MainWindow::poll_events(u16& frame_updates_requested, bool wait){
+    SDL_Event event;
+    if(wait){
+        // waits for first event in cpu-efficient way
+        SDL_TRY(SDL_WaitEvent(&event) != 1); 
+    }
+    // dont wait for event
+    else if(!SDL_PollEvent(&event))
+        return;
+    
+    do {
+        if(ImGui_ImplSDL2_ProcessEvent(&event))
+            frame_updates_requested=2;
+        switch(event.type){
+            case SDL_QUIT: {
+                close();
+                break;
+            }
+            case SDL_WINDOWEVENT: {
+                if(event.window.event == SDL_WINDOWEVENT_CLOSE && event.window.windowID == SDL_GetWindowID(sdl_window)){
+                    close();
+                }
+                break;
+            }
+        }
+    } while (SDL_PollEvent(&event)); // if there are more events, handles them
+}
+
+void ImGui_drawErrorWindow(bool* draw_error_window, std::string& msg){
+    ImGui::Begin("ERROR", draw_error_window);
+        ImGui::Text("%s", msg.c_str());
+    ImGui::End();
+}
+
+void MainWindow::draw_ui(){
+    static std::string error_message;
+    static bool draw_error_window = false;
+    try {
+        // Draw UI
+        if(draw_error_window)
+            ImGui_drawErrorWindow(&draw_error_window, error_message);
+        else {
+            draw_bg_window();
+            draw_debug_window();
+        }
+    }
+    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 MainWindow::draw_frame(){
+    // Start the Dear ImGui frame
+    ImGui_ImplOpenGL3_NewFrame();
+    ImGui_ImplSDL2_NewFrame();
+    ImGui::NewFrame();
+
+    draw_ui();
+
+    // Rendering
+    ImGui::Render();
+    ImGuiIO& io = ImGui::GetIO();
+    glViewport(0, 0, (int)io.DisplaySize.x, (int)io.DisplaySize.y);
+    glClearColor(clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w);
+    glClear(GL_COLOR_BUFFER_BIT);
+    ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
+
+    // Update and Render additional Platform Windows
+    // (Platform functions may change the current OpenGL context, so we save/restore it to make it easier to paste this code elsewhere.
+    //  For this specific demo app we could also call SDL_GL_MakeCurrent(window, gl_context) directly)
+    if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
+    {
+        SDL_Window* backup_current_window = SDL_GL_GetCurrentWindow();
+        SDL_GLContext backup_current_context = SDL_GL_GetCurrentContext();
+        ImGui::UpdatePlatformWindows();
+        ImGui::RenderPlatformWindowsDefault();
+        SDL_GL_MakeCurrent(backup_current_window, backup_current_context);
+    }
+
+    SDL_GL_SwapWindow(sdl_window);
+
+}
+
+void MainWindow::startAndWait(){
+    if(loop_running)
+        throw UsefulException("loop is already running");
+
+    // draw first frame
+    draw_frame();
+
+    u16 frame_updates_requested=1;
+    u64 prev_update_time_ms=SDL_GetTicks64();
+    loop_running=true;
+    // main loop
+    while(loop_running){
+        // waits for events
+        poll_events(frame_updates_requested, main_loop_wait_for_input);
+
+        if(frame_updates_requested==0)
+        {
+            u64 update_time_ms=SDL_GetTicks64();
+            if(update_time_ms >= prev_update_time_ms + 1000/fps_min){
+                // if frame rate < fps_min then requests frame draw
+                // works only if main_loop_wait_for_input = false
+                frame_updates_requested=1;
+                prev_update_time_ms=update_time_ms;
+            }
+            else {
+                // skips frame rendering and waits to limit fps
+                u32 frame_delay_ms=1000/fps_max;
+                SDL_Delay(frame_delay_ms);
+                continue;
+            }
+        }
+
+        // deaws requested number of frames
+        while(frame_updates_requested>0) {
+            draw_frame();
+            frame_updates_requested--;
+        }   
+    }
+
+    // Cleanup
+    MainWindow::destroy();
+}
+
+void MainWindow::close(){
+    loop_running=false;
+}
+
+void MainWindow::destroy(){
+    ImGui_ImplOpenGL3_Shutdown();
+    ImGui_ImplSDL2_Shutdown();
+    ImGui::DestroyContext();
+    SDL_GL_DeleteContext(gl_context);
+    SDL_DestroyWindow(sdl_window);
+    SDL_Quit();
+}
+
+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();
+
+    ImGui::Begin("Debug Options");
+    ImGui::ColorEdit3("clear_color", (float*)&clear_color);
+    ImGui::Checkbox("main_loop_wait_for_input", &main_loop_wait_for_input);
+    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..94a1094
--- /dev/null
+++ b/src/GUI/MainWindow.hpp
@@ -0,0 +1,51 @@
+#pragma once
+
+#include <SDL.h>
+#include <SDL_opengl.h>
+#include <imgui.h>
+#include <iostream>
+#include <string>
+#include "../std.hpp"
+#include "../format.hpp"
+#include "exceptions.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 "DroidSans"
+
+class MainWindow {
+public:
+    ImVec4 clear_color = RGBAHexToF(35,35,50,255);
+    f32 default_font_size = 14.0f;
+    u8 fps_min = 30;
+    u8 fps_max = 60;
+
+private:
+    bool loop_running=false;
+    bool main_loop_wait_for_input=true;
+    bool show_demo_window = false;
+    bool show_metrics_window = false;
+    SDL_Window* sdl_window = nullptr;
+    SDL_GLContext gl_context = nullptr;
+
+public:
+    void init(const char* window_title);
+    void startAndWait();
+    void close();
+    f32 getDPI();
+
+private:
+    void destroy();
+    void poll_events(u16& frame_updates_requested, bool wait);
+    void draw_frame();
+    void draw_ui();
+    void draw_debug_window();
+    void draw_bg_window();
+};
+
+}
diff --git a/src/GUI/exceptions.cpp b/src/GUI/exceptions.cpp
new file mode 100644
index 0000000..4fc6156
--- /dev/null
+++ b/src/GUI/exceptions.cpp
@@ -0,0 +1,12 @@
+#include "exceptions.hpp"
+#include <SDL.h>
+
+namespace ougge::GUI {
+
+SDLException_::SDLException_(const std::string& _file,const  std::string& _func, int _line_n)
+    : UsefulException_(SDL_GetError(), _file, _func, _line_n)
+{
+    SDL_ClearError();
+}
+
+}
diff --git a/src/GUI/exceptions.hpp b/src/GUI/exceptions.hpp
new file mode 100644
index 0000000..4b3b563
--- /dev/null
+++ b/src/GUI/exceptions.hpp
@@ -0,0 +1,16 @@
+#pragma once
+
+#include "../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 SDL_TRY(EXPR) if(EXPR) throw SDLException();
+
+}
diff --git a/src/format.hpp b/src/format.hpp
index bf7b4b6..493df97 100644
--- a/src/format.hpp
+++ b/src/format.hpp
@@ -1,7 +1,7 @@
 #pragma once
 
 #include <string>
-#include "../dependencies/kerep/src/base/std.h"
+#include "std.hpp"
 
 std::string _format(const std::string& format_str, const size_t args_count, ...);
 #define format(FORMAT_STR, ARGS...) _format(FORMAT_STR, count_args(ARGS) ,##ARGS)
diff --git a/src/main.cpp b/src/main.cpp
index 20eeefc..cbb22f3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,9 +1,34 @@
 #define SDL_MAIN_HANDLED
-#include <SDL.h>
+#include "GUI/MainWindow.hpp"
 #include "std.hpp"
 #include <iostream>
 
+using namespace ougge;
+
 int main(int argc, const char** argv){
-    std::cout<<"UwU"<<std::endl;
+    if(setlocale(LC_CTYPE, "C.UTF-8")!=0)
+        std::cerr<<"\e[93msetlocale failed!\n";
+
+    try {
+        GUI::MainWindow w;
+        w.init("ougge");
+        w.startAndWait();
+    }
+    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;
 }