diff --git a/.ccls b/.ccls
index 68cd814..a91784d 100644
--- a/.ccls
+++ b/.ccls
@@ -1,6 +1,8 @@
-clang++
+clangd
 -std=c++17
 -DDEBUG
+-Wall
+-Wconversion
 -Iinclude
 -I/usr/include/freetype2
 -I/usr/include/libpng16
diff --git a/.clang-format b/.clang-format
index f54912e..3efd2bd 100644
--- a/.clang-format
+++ b/.clang-format
@@ -1,5 +1,5 @@
 BasedOnStyle: Microsoft
-AccessModifierOffset: -3
+AccessModifierOffset: -4
 AlignAfterOpenBracket: AlwaysBreak
 AlignConsecutiveAssignments: None
 AlignConsecutiveBitFields: None
@@ -21,7 +21,7 @@ AllowShortLoopsOnASingleLine: true
 AlwaysBreakAfterReturnType: None
 AlwaysBreakBeforeMultilineStrings: false
 AlwaysBreakTemplateDeclarations: No
-AttributeMacros: ['__ununsed']
+AttributeMacros: ['__unused']
 BinPackArguments: true
 BinPackParameters: true
 BitFieldColonSpacing: Both
@@ -50,12 +50,13 @@ BreakBeforeTernaryOperators: true
 BreakConstructorInitializers: AfterColon
 BreakInheritanceList: AfterColon
 BreakStringLiterals: true
-ColumnLimit: 140
+ColumnLimit: 120
 CompactNamespaces: false
 ConstructorInitializerAllOnOneLineOrOnePerLine: false
 Cpp11BracedListStyle: true
 DeriveLineEnding: true
 DerivePointerAlignment: false
+EmptyLineAfterAccessModifier: Never
 EmptyLineBeforeAccessModifier: LogicalBlock
 FixNamespaceComments: true
 IncludeBlocks: Regroup
@@ -78,13 +79,14 @@ IncludeCategories:
   - Regex: '^"'
     Priority: 4
     SortPriority: 4
+IndentAccessModifiers: false
 IndentCaseBlocks: true
 IndentCaseLabels: true
 IndentExternBlock: NoIndent
 IndentGotoLabels: false
 IndentPPDirectives: BeforeHash
 IndentRequires: true
-IndentWidth: 3
+IndentWidth: 4
 IndentWrappedFunctionNames: false
 InsertTrailingCommas: None
 KeepEmptyLinesAtTheStartOfBlocks: false
@@ -116,6 +118,6 @@ SpacesInContainerLiterals: false
 SpacesInParentheses: false
 SpacesInSquareBrackets: false
 Standard: c++17
-TabWidth: 3
+TabWidth: 4
 UseCRLF: false
-UseTab: Always
\ No newline at end of file
+UseTab: Always
diff --git a/.gitignore b/.gitignore
index f6d5daf..68174dc 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 .#.*
 *.kdev4
+*.ttf
 
 .ccls-cache
 .kdev4
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f3cd877
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# UUI
+
+Simple and efficient C++ GUI toolkit
diff --git a/ROADMAP.md b/ROADMAP.md
new file mode 100644
index 0000000..b85818b
--- /dev/null
+++ b/ROADMAP.md
@@ -0,0 +1,21 @@
+* button
+
+* scroll
+
+* Text wrap
+
+* Style
+
+* Text Edition
+
+* projected vertex/raw vertex mode (projection on GPU)
+
+* negative absolute position (from right/bottom)
+
+* VAO/VBO in windows (batched)
+
+* pool/wait mode mechanism
+
+* better font rendering : signed distance
+
+* Rich text component : parsing html? making list of struct of texts (with style information for the rendering)
diff --git a/include/uui/application.hpp b/include/uui/application.hpp
index 151ca36..7d813a0 100644
--- a/include/uui/application.hpp
+++ b/include/uui/application.hpp
@@ -3,17 +3,39 @@
 #include <memory>
 #include <string>
 
-#include "window.hpp"
+#include "uui/types.hpp"
 
 namespace uui
 {
+class Window;
 class Application
 {
 public:
+#ifdef DEBUG
+	constexpr static bool debug_mode = true;
+#else
+	constexpr static bool debug_mode = false;
+#endif
+	enum Implementaion
+	{
+		OPENGL
+	};
+
 	virtual void run() = 0;
-	// virtual std::weak_ptr<Window> add_window(int width, int height, const std::string& title) = 0;
+	virtual void create_window(int width, int height, const std::string& title, InitFunction<Window> init) = 0;
+	virtual std::shared_ptr<Window> get_window(std::size_t index [[maybe_unused]]) const = 0;
+	virtual ~Application() {};
 
 protected:
-	static bool application_created;
+	static std::shared_ptr<Application> current_application;
+
+	bool initialized;
+
+	virtual void init() = 0;
+	virtual void deinit() = 0;
+
+	friend std::shared_ptr<Application> create_application(Application::Implementaion implementation);
 };
+
+std::shared_ptr<Application> create_application(Application::Implementaion implementation);
 } // namespace uui
diff --git a/include/uui/component.hpp b/include/uui/component.hpp
index 7e41fc9..ef91c34 100644
--- a/include/uui/component.hpp
+++ b/include/uui/component.hpp
@@ -1,31 +1,45 @@
 #pragma once
 
 #include <array>
-#include <variant>
+#include <memory>
+
+#include "uui/types.hpp"
+#include "uui/window.hpp"
 
 namespace uui
 {
+class Container;
 class Component
 {
 public:
-	Component(
-		 const std::variant<int, float> x, const std::variant<int, float> y, const std::variant<int, float> width,
-		 const std::variant<int, float> height):
-		 position_x(x),
-		 position_y(y), size_width(width), size_height(height)
-	{
-		background_color = {0.0f, 0.0f, 0.0f, 0.0f};
-	}
+	virtual void set_background_color(float r, float g, float b, float a = 1.0f) = 0;
 
-	virtual void render() = 0;
+	ComponentType type() { return _type; }
+	uui::position_t x() { return _position_x; }
+	uui::position_t y() { return _position_y; }
+	uui::size_t width() { return _width; }
+	uui::size_t height() { return _height; }
 
 protected:
-	std::variant<int, float> position_x;
-	std::variant<int, float> position_y;
-	std::variant<int, float> size_width;
-	std::variant<int, float> size_height;
+	ComponentType _type = ComponentType::UNASSIGNED;
 
-	std::array<float, 4> background_color;
+	std::shared_ptr<Window> _window;
+	std::size_t _window_index;
+	std::shared_ptr<Container> _parent;
+	std::size_t _parent_index;
+
+	uui::position_t _position_x;
+	uui::position_t _position_y;
+	uui::size_t _width;
+	uui::size_t _height;
+
+	bool _coord_all_relative;
+
+	std::array<float, 4> _background_color;
+
+	bool _initialized = false;
+
+	virtual void render() = 0;
 };
 
 } // namespace uui
diff --git a/include/uui/config.hpp b/include/uui/config.hpp
deleted file mode 100644
index 1afb3a0..0000000
--- a/include/uui/config.hpp
+++ /dev/null
@@ -1,8 +0,0 @@
-#pragma once
-
-#include "graphic_context.hpp"
-
-namespace Config
-{
-constexpr unsigned int FONT_TEXTURE_UNIT = GL_TEXTURE0;
-}
diff --git a/include/uui/container.hpp b/include/uui/container.hpp
new file mode 100644
index 0000000..782ff97
--- /dev/null
+++ b/include/uui/container.hpp
@@ -0,0 +1,12 @@
+#pragma once
+
+#include "uui/component.hpp"
+#include "uui/container_interface.hpp"
+#include "uui/types.hpp"
+
+namespace uui
+{
+class Container: virtual public Component, virtual public ContainerInterface
+{};
+
+} // namespace uui
diff --git a/include/uui/container_interface.hpp b/include/uui/container_interface.hpp
new file mode 100644
index 0000000..e43f496
--- /dev/null
+++ b/include/uui/container_interface.hpp
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <memory>
+#include <tuple>
+
+#include "uui/types.hpp"
+
+namespace uui
+{
+class Component;
+class ContainerInterface
+{
+public:
+	virtual std::tuple<int, int> get_child_position(const std::size_t child_index [[maybe_unused]]) const = 0;
+
+protected:
+	virtual std::size_t push_child(std::shared_ptr<Component> child) = 0;
+	virtual std::shared_ptr<Component> get_child(std::size_t index) const = 0;
+	virtual void remove_child(std::size_t index) = 0;
+};
+
+} // namespace uui
diff --git a/include/uui/flex.hpp b/include/uui/flex.hpp
new file mode 100644
index 0000000..1adf974
--- /dev/null
+++ b/include/uui/flex.hpp
@@ -0,0 +1,16 @@
+#pragma once
+
+#include <string>
+#include <tuple>
+
+#include "uui/stack.hpp"
+
+namespace uui
+{
+class Flex: virtual public Stack
+{
+protected:
+	virtual std::tuple<int, int> get_child_position(const std::size_t child_index) const = 0;
+};
+
+} // namespace uui
diff --git a/include/uui/font_manager.hpp b/include/uui/font_manager.hpp
new file mode 100644
index 0000000..52da172
--- /dev/null
+++ b/include/uui/font_manager.hpp
@@ -0,0 +1,56 @@
+#pragma once
+
+#include <string>
+#include <tuple>
+#include <vector>
+
+#include <ft2build.h>
+#include FT_FREETYPE_H
+
+namespace uui
+{
+class Window;
+class FontManager
+{
+	friend class Window;
+
+public:
+	struct character_info
+	{
+		float advance_x; // advance.x
+		float advance_y; // advance.y
+
+		float bitmap_width; // bitmap.width;
+		float bitmap_height; // bitmap.rows;
+
+		float bitmap_left; // bitmap_left;
+		float bitmap_top; // bitmap_top;
+
+		float texture_x; // x offset of glyph in texture coordinates
+		float texture_y; // y offset of glyph in texture coordinates
+	};
+
+	struct Font
+	{
+		character_info char_infos[256];
+		unsigned int atlas_texture;
+		unsigned int atlas_width;
+		unsigned int atlas_height;
+	};
+
+	std::vector<Font> fonts;
+
+	virtual void render_text(
+		const std::string& text, Font& font, float x, float y, float scale_x, float scale_y,
+		const std::tuple<float, float, float, float>& text_color) = 0;
+	virtual std::tuple<int, int> get_text_size(const std::string& text, Font& font, float scale_x, float scale_y) = 0;
+
+protected:
+	static constexpr int ATLAS_MAX_WIDTH = 1024;
+
+	bool initialized;
+
+	FT_Library ft;
+	virtual const Font& init_font(const std::string& font_path, unsigned int font_size) = 0;
+};
+} // namespace uui
diff --git a/include/uui/label.hpp b/include/uui/label.hpp
new file mode 100644
index 0000000..2de7c22
--- /dev/null
+++ b/include/uui/label.hpp
@@ -0,0 +1,22 @@
+#pragma once
+
+#include <string>
+#include <tuple>
+
+#include "uui/component.hpp"
+
+namespace uui
+{
+class Label: virtual public Component
+{
+protected:
+	std::size_t font_index;
+
+	std::string text;
+	std::tuple<float, float, float, float> text_color;
+
+	int text_width;
+	int text_height;
+};
+
+} // namespace uui
diff --git a/include/uui/opengl/application.hpp b/include/uui/opengl/application.hpp
index df15fe4..4d2d4e6 100644
--- a/include/uui/opengl/application.hpp
+++ b/include/uui/opengl/application.hpp
@@ -2,89 +2,32 @@
 
 #include <memory>
 #include <string>
-#include <variant>
 #include <vector>
 
 #include "graphic_context.hpp"
-#include "uui/opengl/font_manager.hpp"
+#include "uui/application.hpp"
+#include "uui/types.hpp"
 
 namespace uui
 {
 class GlWindow;
-class GlApplication
+class GlApplication final: virtual public Application
 {
 	friend class GlWindow;
 
 public:
-#ifdef DEBUG
-	constexpr static bool debug_mode = true;
-#else
-	constexpr static bool debug_mode = false;
-#endif
 	std::vector<std::shared_ptr<GlWindow>> windows;
 
 	GlApplication();
-	~GlApplication();
+	virtual ~GlApplication() final;
 
-	void run();
-	std::shared_ptr<GlWindow> create_window(int width, int height, const std::string& title);
-	std::shared_ptr<GlWindow> get_window(size_t index) const;
-
-private:
-	static GlApplication* application_pointer;
-};
-
-class GlLabel;
-class GlComponent;
-class GlWindow
-{
-	friend class GlApplication;
-	friend class GlComponent;
-	friend class GlLabel;
-
-public:
-	std::string title;
-	std::vector<std::shared_ptr<GlComponent>> components;
-
-	GlWindow(const GlWindow&) = delete;
-	GlWindow(GlWindow&&) = delete;
-	~GlWindow();
-
-	std::shared_ptr<GlComponent> create_component(
-		 const std::variant<int, float> x, const std::variant<int, float> y, const std::variant<int, float> width,
-		 const std::variant<int, float> height);
-	std::shared_ptr<GlLabel> create_label(
-		 const std::variant<int, float> x, const std::variant<int, float> y, const std::string& text,
-		 const std::tuple<float, float, float, float>& text_color);
+	void run() final;
+	void create_window(int width, int height, const std::string& title, InitFunction<Window> init) final;
+	std::shared_ptr<Window> get_window(std::size_t index) const final;
 
 protected:
-	GlApplication* app;
-
-	GlFontManager font_manager;
-
-	int width;
-	int height;
-	bool render_needed;
-	bool resize_needed;
-
-	bool iconified;
-
-	size_t index;
-	bool initialized;
-
-	GLFWwindow* glfw_window;
-
-	GLuint gl_program;
-
-	GlWindow(GlApplication* app, size_t index, int width, int height, const std::string& title);
-
-	void init();
-	void deinit();
-	void render();
-
-	static void glfw_resize_callback(GLFWwindow* window, int width, int height);
-	static void glfw_iconify_callback(GLFWwindow* window, int iconified);
-	static void glfw_key_callback(GLFWwindow* window, int key, int scancode, int action, int mods);
+	void init() final;
+	void deinit() final;
 };
 
 } // namespace uui
diff --git a/include/uui/opengl/button.hpp b/include/uui/opengl/button.hpp
new file mode 100644
index 0000000..0df1ff2
--- /dev/null
+++ b/include/uui/opengl/button.hpp
@@ -0,0 +1,27 @@
+#pragma once
+
+#include <memory>
+#include <string>
+#include <tuple>
+
+#include "uui/opengl/component.hpp"
+
+namespace uui
+{
+class GlButton: public GlComponent
+{
+	friend class GlWindow;
+
+protected:
+	GlButton(
+		std::shared_ptr<GlWindow> window, std::size_t window_index, std::shared_ptr<GlContainer> parent,
+		std::size_t parent_index, const position_t x, const position_t y, const Direction direction);
+	GlButton(
+		std::shared_ptr<GlWindow> window, std::size_t window_index, const position_t x, const position_t y,
+		const Direction direction): GlButton(window, window_index, window, window_index, x, y, direction)
+	{}
+
+	virtual std::tuple<int, int> get_child_position(const std::size_t child_index) const;
+};
+
+} // namespace uui
diff --git a/include/uui/opengl/component.hpp b/include/uui/opengl/component.hpp
index b2c57bc..6ecaa99 100644
--- a/include/uui/opengl/component.hpp
+++ b/include/uui/opengl/component.hpp
@@ -2,49 +2,50 @@
 
 #include <array>
 #include <memory>
-#include <variant>
 
-#include "graphic_context.hpp"
-#include "window.hpp"
+#include "uui/component.hpp"
+#include "uui/opengl/graphic_context.hpp"
+#include "uui/opengl/window.hpp"
+#include "uui/types.hpp"
 
 namespace uui
 {
-class GlComponent
+class GlContainer;
+class GlFlex;
+class GlStack;
+class GlComponent: public std::enable_shared_from_this<GlComponent>, virtual public Component
 {
+	friend class GlContainer;
 	friend class GlWindow;
+	friend class GlFlex;
+	friend class GlStack;
 
 public:
-	GlComponent(const GlComponent&) = delete;
-	GlComponent(GlComponent&&) = delete;
-	~GlComponent();
+	virtual ~GlComponent();
 
-	void set_background_color(float r, float g, float b, float a = 1.0f);
+	void set_background_color(float r, float g, float b, float a = 1.0f) final;
 
 protected:
-	std::shared_ptr<GlWindow> window;
-
-	std::variant<int, float> position_x;
-	std::variant<int, float> position_y;
-	std::variant<int, float> size_width;
-	std::variant<int, float> size_height;
-	bool coord_all_relative;
-
-	std::array<float, 4> background_color;
-
-	bool initialized;
-
+	std::shared_ptr<GlWindow> gl_window;
 	GLuint gl_vbo;
 	GLuint gl_vao;
 	GLuint gl_ebo;
 
 	GlComponent(
-		 std::shared_ptr<GlWindow> window, const std::variant<int, float> x, const std::variant<int, float> y,
-		 const std::variant<int, float> width, const std::variant<int, float> height);
+		std::shared_ptr<GlWindow> window, std::size_t window_index, std::shared_ptr<GlContainer> parent,
+		std::size_t parent_index, const ComponentParams& params);
+	GlComponent(std::shared_ptr<GlWindow> window, std::size_t window_index, const ComponentParams& params):
+		GlComponent(window, window_index, nullptr, 0, params)
+	{}
+	GlComponent(const GlComponent&) = delete;
+	GlComponent(GlComponent&&) = default;
+	std::shared_ptr<GlComponent> getptr() { return shared_from_this(); }
+
+	virtual void render();
 
 	virtual void init();
 	virtual void set_vbo_data();
 	virtual void deinit();
-	virtual void render();
 	virtual void on_resize();
 };
 
diff --git a/include/uui/opengl/container.hpp b/include/uui/opengl/container.hpp
new file mode 100644
index 0000000..8deaf6d
--- /dev/null
+++ b/include/uui/opengl/container.hpp
@@ -0,0 +1,18 @@
+#pragma once
+
+#include <cstdlib>
+
+#include <iostream>
+#include <memory>
+#include <vector>
+
+#include "uui/container.hpp"
+#include "uui/opengl/component.hpp"
+#include "uui/opengl/container_interface.hpp"
+
+namespace uui
+{
+class GlContainer: virtual public Container, virtual public GlContainerInterface
+{};
+
+} // namespace uui
diff --git a/include/uui/opengl/container_interface.hpp b/include/uui/opengl/container_interface.hpp
new file mode 100644
index 0000000..e068ffa
--- /dev/null
+++ b/include/uui/opengl/container_interface.hpp
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <memory>
+#include <tuple>
+
+#include "uui/component.hpp"
+#include "uui/container_interface.hpp"
+#include "uui/types.hpp"
+
+namespace uui
+{
+class GlComponent;
+class GlContainerInterface: virtual public ContainerInterface
+{
+public:
+	virtual std::tuple<int, int> get_child_position(const std::size_t child_index [[maybe_unused]]) const override;
+
+protected:
+	virtual std::size_t push_child(std::shared_ptr<Component> child) final;
+	std::size_t push_child(std::shared_ptr<GlComponent> child);
+	virtual std::shared_ptr<Component> get_child(std::size_t index) const final;
+	virtual void remove_child(std::size_t index) final;
+
+	virtual ~GlContainerInterface();
+
+	std::vector<std::shared_ptr<GlComponent>> components;
+};
+} // namespace uui
diff --git a/include/uui/opengl/flex.hpp b/include/uui/opengl/flex.hpp
new file mode 100644
index 0000000..975d30c
--- /dev/null
+++ b/include/uui/opengl/flex.hpp
@@ -0,0 +1,29 @@
+#pragma once
+
+#include <memory>
+#include <string>
+#include <tuple>
+
+#include "uui/flex.hpp"
+#include "uui/opengl/container.hpp"
+#include "uui/opengl/stack.hpp"
+#include "uui/opengl/window.hpp"
+
+namespace uui
+{
+class GlFlex: virtual public GlStack, virtual public Flex
+{
+	friend class GlWindow;
+
+protected:
+	GlFlex(
+		std::shared_ptr<GlWindow> window, std::size_t window_index, std::shared_ptr<GlContainer> parent,
+		std::size_t parent_index, const StackParams& params);
+	GlFlex(std::shared_ptr<GlWindow> window, std::size_t window_index, const StackParams& params):
+		GlFlex(window, window_index, nullptr, 0, params)
+	{}
+
+	std::tuple<int, int> get_child_position(const std::size_t child_index) const override;
+};
+
+} // namespace uui
diff --git a/include/uui/opengl/font_manager.hpp b/include/uui/opengl/font_manager.hpp
index 07184a5..e797f1b 100644
--- a/include/uui/opengl/font_manager.hpp
+++ b/include/uui/opengl/font_manager.hpp
@@ -5,64 +5,32 @@
 #include <tuple>
 #include <vector>
 
-#include <ft2build.h>
-#include FT_FREETYPE_H
-#include "graphic_context.hpp"
+#include "uui/font_manager.hpp"
+#include "uui/opengl/graphic_context.hpp"
 
 namespace uui
 {
 class GlWindow;
-class GlFontManager
+class GlFontManager final: public FontManager
 {
 	friend class GlWindow;
 
 public:
-	struct character_info
-	{
-		float advance_x; // advance.x
-		float advance_y; // advance.y
-
-		float bitmap_width; // bitmap.width;
-		float bitmap_height; // bitmap.rows;
-
-		float bitmap_left; // bitmap_left;
-		float bitmap_top; // bitmap_top;
-
-		float texture_x; // x offset of glyph in texture coordinates
-		float texture_y; // y offset of glyph in texture coordinates
-	};
-
-	struct Font
-	{
-		character_info char_infos[256];
-		GLuint atlas_texture;
-		unsigned int atlas_width;
-		unsigned int atlas_height;
-	};
-
-	std::vector<Font> fonts;
-
 	GlFontManager();
 	~GlFontManager();
 
 	void render_text(
-		 const std::string& text, Font& font, float x, float y, float scale_x, float scale_y,
-		 const std::tuple<float, float, float, float>& text_color);
-	std::tuple<int, int> get_text_size(const std::string& text, Font& font, float scale_x, float scale_y);
+		const std::string& text, Font& font, float x, float y, float scale_x, float scale_y,
+		const std::tuple<float, float, float, float>& text_color) final;
+	std::tuple<int, int> get_text_size(const std::string& text, Font& font, float scale_x, float scale_y) final;
 
 private:
-	static constexpr int ATLAS_MAX_WIDTH = 1024;
-
-	bool initialized;
-
-	FT_Library ft;
-
 	GLuint gl_program;
 	GLuint gl_vao;
 	GLuint gl_vbo;
 
 	void init();
 	void deinit();
-	const Font& init_font(const std::string& font_path, size_t font_size);
+	const Font& init_font(const std::string& font_path, unsigned int font_size);
 };
 } // namespace uui
diff --git a/include/graphic_context.hpp b/include/uui/opengl/graphic_context.hpp
similarity index 65%
rename from include/graphic_context.hpp
rename to include/uui/opengl/graphic_context.hpp
index 800a70d..037f696 100644
--- a/include/graphic_context.hpp
+++ b/include/uui/opengl/graphic_context.hpp
@@ -1,8 +1,9 @@
 #pragma once
 
 // clang-format off
+#define GLAD_GL_IMPLEMENTATION
 #include "glad/glad.h"
-#define GLFW_INCLUDE_VULKAN
+#define GLFW_INCLUDE_NONE
 #include <GLFW/glfw3.h>
 
 #define GLM_FORCE_RADIANS
@@ -11,3 +12,8 @@
 #include <glm/gtc/matrix_transform.hpp>
 #include <glm/gtc/type_ptr.hpp>
 // clang-format off
+
+namespace GlConfig
+{
+	constexpr unsigned int FONT_TEXTURE_UNIT = GL_TEXTURE0;
+}
diff --git a/include/uui/opengl/label.hpp b/include/uui/opengl/label.hpp
index fcb1d24..266b615 100644
--- a/include/uui/opengl/label.hpp
+++ b/include/uui/opengl/label.hpp
@@ -3,18 +3,20 @@
 #include <string>
 #include <tuple>
 
+#include "uui/label.hpp"
 #include "uui/opengl/component.hpp"
+#include "uui/opengl/container.hpp"
+#include "uui/opengl/window.hpp"
 
 namespace uui
 {
-class GlLabel: public GlComponent
+class GlFlex;
+class GlStack;
+class GlLabel final: virtual public GlComponent, virtual public Label
 {
 	friend class GlWindow;
-
-	size_t font_index;
-
-	float get_width() const;
-	float get_height() const;
+	friend class GlFlex;
+	friend class GlStack;
 
 protected:
 	std::string text;
@@ -24,10 +26,13 @@ protected:
 	int text_height;
 
 	GlLabel(
-		 std::shared_ptr<GlWindow> window, const std::variant<int, float> x, const std::variant<int, float> y, const std::string& text,
-		 const std::tuple<float, float, float, float>& text_color);
+		std::shared_ptr<GlWindow> window, std::size_t window_index, std::shared_ptr<GlContainer> parent,
+		std::size_t parent_index, const LabelParams& params);
+	GlLabel(std::shared_ptr<GlWindow> window, std::size_t window_index, const LabelParams& params):
+		GlLabel(window, window_index, nullptr, 0, params)
+	{}
 
-	void render();
+	void render() final;
 };
 
 } // namespace uui
diff --git a/include/uui/opengl/stack.hpp b/include/uui/opengl/stack.hpp
new file mode 100644
index 0000000..52310c4
--- /dev/null
+++ b/include/uui/opengl/stack.hpp
@@ -0,0 +1,32 @@
+#pragma once
+
+#include <memory>
+#include <string>
+#include <tuple>
+
+#include "uui/opengl/component.hpp"
+#include "uui/opengl/container.hpp"
+#include "uui/stack.hpp"
+
+namespace uui
+{
+class GlStack: virtual public GlComponent, virtual public GlContainer, virtual public Stack
+{
+	friend class GlWindow;
+
+public:
+	void create_component(const StackComponentParams& params, InitFunction<Component> init) override;
+	void create_label(const StackLabelParams& params, InitFunction<Label> init) override;
+
+protected:
+	GlStack(
+		std::shared_ptr<GlWindow> window, std::size_t window_index, std::shared_ptr<GlContainer> parent,
+		std::size_t parent_index, const StackParams& params);
+	GlStack(std::shared_ptr<GlWindow> window, std::size_t window_index, const StackParams& params):
+		GlStack(window, window_index, nullptr, 0, params)
+	{}
+
+	std::tuple<int, int> get_child_position(const std::size_t child_index) const override;
+};
+
+} // namespace uui
diff --git a/include/uui/opengl/window.hpp b/include/uui/opengl/window.hpp
index dd3f0d0..6a5ab32 100644
--- a/include/uui/opengl/window.hpp
+++ b/include/uui/opengl/window.hpp
@@ -1,3 +1,56 @@
 #pragma once
 
 #include "uui/opengl/application.hpp"
+#include "uui/opengl/container_interface.hpp"
+#include "uui/opengl/font_manager.hpp"
+#include "uui/types.hpp"
+#include "uui/window.hpp"
+
+namespace uui
+{
+class GlComponent;
+class GlContainer;
+class GlFlex;
+class GlLabel;
+class GlStack;
+class GlWindow:
+	public std::enable_shared_from_this<GlWindow>,
+	virtual public Window,
+	virtual public GlContainerInterface
+{
+	friend class GlApplication;
+	friend class GlComponent;
+	friend class GlFlex;
+	friend class GlLabel;
+	friend class GlStack;
+
+public:
+	GlWindow(const GlWindow&) = delete;
+	GlWindow(GlWindow&&) = delete;
+	~GlWindow();
+
+	void create_component(const ComponentParams& params, InitFunction<Component> init) final;
+	void create_label(const LabelParams& params, InitFunction<Label> init) final;
+	void create_flex(const StackParams& params, InitFunction<Flex> init) final;
+	void create_stack(const StackParams& params, InitFunction<Stack> init) final;
+
+protected:
+	void render() final;
+
+	std::shared_ptr<GlFontManager> gl_font_manager;
+
+	GLFWwindow* glfw_window;
+	GLuint gl_program;
+
+	GlWindow(std::shared_ptr<Application> app, int width, int height, const std::string& title);
+	std::shared_ptr<GlWindow> getptr() { return shared_from_this(); }
+
+	void init();
+	void deinit();
+
+	static void glfw_resize_callback(GLFWwindow* window, int width, int height);
+	static void glfw_iconify_callback(GLFWwindow* window, int iconified);
+	static void glfw_key_callback(GLFWwindow* window, int key, int scancode, int action, int mods);
+	// static void glfw_mouse_button_callback(GLFWwindow* window, int button, int action, int mods);
+};
+} // namespace uui
diff --git a/include/uui/stack.hpp b/include/uui/stack.hpp
new file mode 100644
index 0000000..df89240
--- /dev/null
+++ b/include/uui/stack.hpp
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <string>
+#include <tuple>
+
+#include "uui/component.hpp"
+#include "uui/label.hpp"
+
+namespace uui
+{
+class Stack: virtual public Component
+{
+public:
+	virtual void create_component(const StackComponentParams& params, InitFunction<Component> init) = 0;
+	virtual void create_label(const StackLabelParams& params, InitFunction<Label> init) = 0;
+
+protected:
+	Direction direction;
+	int content_width;
+	int content_height;
+
+	virtual std::tuple<int, int> get_child_position(const std::size_t child_index) const = 0;
+};
+
+} // namespace uui
diff --git a/include/uui/style.hpp b/include/uui/style.hpp
new file mode 100644
index 0000000..c3d4781
--- /dev/null
+++ b/include/uui/style.hpp
@@ -0,0 +1,46 @@
+#pragma once
+
+#include <memory>
+#include <optional>
+#include <tuple>
+
+#include "types.hpp"
+
+namespace uui
+{
+struct Style
+{
+	enum Position
+	{
+		RELATIVE,
+		ABSOLUTE
+	};
+	enum Alignment
+	{
+		START,
+		CENTER,
+		END
+	};
+	struct AbsolutePostion
+	{
+		std::optional<position_t> left;
+		std::optional<position_t> right;
+		std::optional<position_t> top;
+		std::optional<position_t> bottom;
+	};
+
+	// Layout
+	Position position;
+	Alignment horizontal_alignment;
+	Alignment vertical_alignment;
+	std::optional<uui::size_t> width;
+	std::optional<uui::size_t> height;
+	std::optional<uui::size_t> margin;
+	std::optional<uui::size_t> padding;
+	// For absolute positioning
+	std::unique_ptr<AbsolutePostion> absolute_position;
+
+	// Color
+	std::optional<std::tuple<float, float, float, float>> background_color;
+};
+} // namespace uui
diff --git a/include/uui/types.hpp b/include/uui/types.hpp
new file mode 100644
index 0000000..d329768
--- /dev/null
+++ b/include/uui/types.hpp
@@ -0,0 +1,67 @@
+#pragma once
+
+#include <functional>
+#include <tuple>
+#include <variant>
+
+namespace uui
+{
+namespace Config
+{
+constexpr int MOUSE_GRID_WIDTH = 20;
+constexpr int MOUSE_GRID_HEIGHT = 20;
+}; // namespace Config
+
+template<typename T> using InitFunction = const std::function<void(T&)>&;
+typedef std::variant<int, float> position_t;
+typedef std::variant<int, float> size_t;
+typedef std::tuple<float, float, float, float> color_t;
+
+enum class ComponentType
+{
+	UNASSIGNED,
+	COMPONENT,
+	LABEL,
+	FLEX,
+	STACK,
+	WINDOW
+};
+
+enum class Direction
+{
+	HORIZONTAL,
+	VERTICAL
+};
+
+struct ComponentParams
+{
+	uui::position_t x;
+	uui::position_t y;
+	uui::size_t width;
+	uui::size_t height;
+};
+struct LabelParams
+{
+	uui::position_t x;
+	uui::position_t y;
+	const std::string& text;
+	const uui::color_t& text_color;
+};
+struct StackParams
+{
+	const uui::position_t x;
+	const uui::position_t y;
+	const uui::Direction direction;
+};
+struct StackComponentParams
+{
+	uui::size_t width;
+	uui::size_t height;
+};
+struct StackLabelParams
+{
+	const std::string& text;
+	const uui::color_t& text_color;
+};
+
+} // namespace uui
diff --git a/include/uui/uui.hpp b/include/uui/uui.hpp
new file mode 100644
index 0000000..6718260
--- /dev/null
+++ b/include/uui/uui.hpp
@@ -0,0 +1,9 @@
+#pragma once
+
+#include "uui/application.hpp"
+#include "uui/component.hpp"
+#include "uui/flex.hpp"
+#include "uui/label.hpp"
+#include "uui/stack.hpp"
+#include "uui/types.hpp"
+#include "uui/window.hpp"
diff --git a/include/uui/window.hpp b/include/uui/window.hpp
index b5d6c49..16abe65 100644
--- a/include/uui/window.hpp
+++ b/include/uui/window.hpp
@@ -1,24 +1,52 @@
 #pragma once
 
+#include <array>
 #include <memory>
 #include <string>
-#include <vector>
 
-#include "graphic_context.hpp"
-#include "uui/component.hpp"
+#include "uui/application.hpp"
+#include "uui/container_interface.hpp"
+#include "uui/font_manager.hpp"
+#include "uui/types.hpp"
 
 namespace uui
 {
-class Window
+class Component;
+class Label;
+class Flex;
+class Stack;
+class Window: virtual public ContainerInterface
 {
-public:
-	std::string title;
+	friend class Component;
 
-	virtual void add_component(const Component& box) = 0;
+public:
+	std::shared_ptr<FontManager> font_manager;
+
+	virtual void create_component(const ComponentParams& params, InitFunction<Component> init) = 0;
+	virtual void create_label(const LabelParams& params, InitFunction<Label> init) = 0;
+	virtual void create_flex(const StackParams& params, InitFunction<Flex> init) = 0;
+	virtual void create_stack(const StackParams& params, InitFunction<Stack> init) = 0;
+
+	const std::string& title() { return _title; }
+	int width() { return _width; };
+	int height() { return _height; };
 
 protected:
-	GLFWwindow* glfw_window;
+	ComponentType _type = ComponentType::UNASSIGNED;
 
-	virtual void draw() = 0;
+	std::shared_ptr<Application> _app;
+	bool _initialized;
+
+	std::string _title;
+	int _width;
+	int _height;
+	bool _render_needed;
+	bool _resize_needed;
+	bool _iconified;
+
+	std::array<std::array<std::vector<std::shared_ptr<Component>>, Config::MOUSE_GRID_HEIGHT>, Config::MOUSE_GRID_WIDTH>
+		_grid_click;
+
+	virtual void render() = 0;
 };
 } // namespace uui
diff --git a/make.py b/make.py
index 7799daf..b3b24ce 100644
--- a/make.py
+++ b/make.py
@@ -1,50 +1,38 @@
 #! python3
 
-import os
 from pathlib import Path
 import shutil
 
-from umake import get_hash, make
-
-
-class Config:
-    CC = 'g++'
-    APPS = ['test/example_gl', 'test/benchmark_text']
-    IGNORE_APPS = []
-    JOB_COUNT = int(os.cpu_count() * 0.8)
-
-    BIN_DIR = Path('bin')
-    INCLUDE_DIR = Path('include')
-    OBJECT_DIR = Path('obj')
-    SOURCE_DIR = Path('src')
-
-    COMMON_FLAGS = '-std=c++17 -fno-semantic-interposition'
-    COMMON_DEBUG_FLAGS = '-g -DDEBUG'
-    COMMON_RELEASE_FLAGS = '-O2 -flto'
-    COMPILE_FLAGS = f'-Wall -I{INCLUDE_DIR} `pkg-config --cflags glfw3 vulkan gl x11 freetype2`'
-    LINK_FLAGS = '-lpthread -ldl `pkg-config --libs glfw3 vulkan gl x11 freetype2`'
-
-    PRE_COMPILE_FUNCTION = None
-
-    CPP_SOURCES = [filepath for filepath in SOURCE_DIR.rglob('*.cpp') if not filepath.name.startswith('.')]
+from umake.umake import get_hash, make, Config
 
 
 def main():
+    config = Config()
+
     def pre_compile():
         # Copying OpenGL shaders
-        src_opengl_shader_path = Config.SOURCE_DIR / 'uui' / 'opengl' / 'shaders'
+        src_opengl_shader_path = config.source_dir / 'uui' / 'opengl' / 'shaders'
         for shader_path in (
                 list(src_opengl_shader_path.rglob('*.vert'))
                 + list(src_opengl_shader_path.rglob('*.frag'))):
-            out_path = Config.BIN_DIR / shader_path.relative_to(Config.SOURCE_DIR)
+            out_path = config.bin_dir / shader_path.relative_to(config.source_dir)
             if out_path.exists() and get_hash(shader_path) == get_hash(out_path):
                 continue
             if not out_path.parent.exists():
                 out_path.parent.mkdir(parents=True)
             shutil.copy(shader_path, out_path)
 
-    Config.PRE_COMPILE_FUNCTION = pre_compile
-    make(Config)
+
+    config.apps = [str(p.relative_to(Path('src')))[:-4] for p in (config.source_dir / 'test').rglob('*.cpp')]
+    config.watch = True
+
+    config.common_flags = '-std=c++20 -fno-semantic-interposition'
+    config.common_debug_flags = '-g -Og -DDEBUG'
+    config.common_release_flags = '-O2 -flto=auto'
+    config.compile_flags = f'-Wall -Wextra -Wpedantic -Wconversion -I{config.include_dir} `pkg-config --cflags glfw3 gl x11 freetype2`'
+    config.link_flags = '-lpthread -ldl `pkg-config --libs glfw3 gl freetype2`'
+    config.pre_compile_function = pre_compile
+    make(config)
 
 
 if __name__ == '__main__':
diff --git a/makefile b/makefile
index db2db6a..dde7e0f 100644
--- a/makefile
+++ b/makefile
@@ -1,7 +1,7 @@
 MAKE_PATH="."
 UMAKE_PATH="umake"
 
-.PHONY: all clean
+.PHONY: all watch debug debug_watch clean lint
 
 all:
 	@PYTHONPATH=$(UMAKE_PATH) python $(MAKE_PATH)/make.py
@@ -11,3 +11,6 @@ debug:
 
 clean:
 	@PYTHONPATH=$(UMAKE_PATH) python $(MAKE_PATH)/make.py --clean
+
+lint:
+	@clang-format --dry-run --Werror include/uui/*.hpp include/uui/**/*.hpp src/uui/*.cpp src/uui/**/*.cpp src/test/*.cpp
diff --git a/manifest.md b/manifest.md
index b7f40bd..d817af0 100644
--- a/manifest.md
+++ b/manifest.md
@@ -1,6 +1,5 @@
 # UUI : micro UI Toolkit
 
-
 * C++ + Vulkan/OpenGL
 
 * Python binding
@@ -9,6 +8,10 @@
 
 * Let custom rendering
 
+* Canvas for easy drawing
+
+* Style/Config watch option : real-time update on file change
+
 
 ## Technical
 
@@ -27,4 +30,4 @@
 
 ## Layout / Style
 
-* Constraint based? padding/margin?
+* CSS subset
diff --git a/src/test/benchmark_text.cpp b/src/test/benchmark_text.cpp
index d51a978..9acca2f 100644
--- a/src/test/benchmark_text.cpp
+++ b/src/test/benchmark_text.cpp
@@ -1,8 +1,6 @@
 #include <iostream>
 
-#include "uui/opengl/application.hpp"
-#include "uui/opengl/component.hpp"
-#include "uui/opengl/label.hpp"
+#include "uui/uui.hpp"
 
 using namespace std;
 
@@ -10,12 +8,12 @@ int main()
 {
 	try
 	{
-		uui::GlApplication app;
-		// uui::GlApplication app2; // exception : application already created
-		auto window = app.create_window(800, 600, "OpenGl!");
-		for(int i = 0; i < 100; i += 1)
-			window->create_label(4*i, 4*i, "Hello World!", {1.0f, 1.0f, 1.0f, 0.5f});
-		app.run();
+		auto app = uui::create_application(uui::Application::OPENGL);
+		app->create_window(800, 600, "OpenGl!", [](uui::Window& window) {
+			for(int i = 0; i < 100; i += 1)
+				window.create_label({4 * i, 4 * i, "Hello World!", {1.0f, 1.0f, 1.0f, 0.5f}}, nullptr);
+		});
+		app->run();
 	}
 	catch(const std::exception& error)
 	{
diff --git a/src/test/example_gl.cpp b/src/test/example_gl.cpp
index f1eeb8b..cc50eec 100644
--- a/src/test/example_gl.cpp
+++ b/src/test/example_gl.cpp
@@ -1,8 +1,6 @@
 #include <iostream>
 
-#include "uui/opengl/application.hpp"
-#include "uui/opengl/component.hpp"
-#include "uui/opengl/label.hpp"
+#include "uui/uui.hpp"
 
 using namespace std;
 
@@ -12,36 +10,94 @@ int main()
 	{
 		cout << "Starting example 1" << endl;
 		{
-			uui::GlApplication app;
-			// uui::GlApplication app2; // exception : application already created
-			auto window = app.create_window(800, 600, "OpenGl!");
-			auto comp = window->create_component(0, 100, 0.5f, 50);
-			comp->set_background_color(0.8f, 0.1f, 0.5f);
-			comp = window->create_component(0.25f, 50, 0.4f, 150);
-			comp->set_background_color(0.3f, 0.8f, 0.4f, 0.5f);
-			auto label = window->create_label(50, 50, "Hello World!", {0.5f, 1.0f, 0.5f, 1.0f});
-			label->set_background_color(0.1f, 0.2f, 0.5f, 0.8f);
-			label = window->create_label(0.5f, 0.5f, "Hello World!", {1.0f, 1.0f, 1.0f, 0.5f});
-			label->set_background_color(0.5f, 0.5f, 0.1f);
-			label = window->create_label(0.75f, 0.75f, "Hello World!", {1.0f, 1.0f, 1.0f, 0.1f});
-			app.run();
-		}
-		// cout << "\nStarting example 2" << endl;
-		// {
-		// 	uui::GlApplication app;
-		// 	auto window_1 = app.create_window(800, 600, "OpenGl!");
-		// 	auto comp = window_1->create_component(0.25f, 0.25f, 0.5f, 0.5f);
-		// 	comp->set_background_color(0.8f, 0.1f, 0.5f);
-		// 	comp = window_1->create_component(0.75f, 0.75f, 0.25f, 0.25f);
-		// 	comp->set_background_color(0.2f, 0.1f, 0.5f);
+			auto app = uui::create_application(uui::Application::OPENGL);
+			// auto app2 = uui::create_application(uui::Application::OPENGL); // exception : application already created
+			app->create_window(800, 600, "OpenGl!", [](uui::Window& window) {
+				window.create_component({.x = 0, .y = 100, .width = 0.5f, .height = 50}, [](uui::Component& component) {
+					component.set_background_color(0.8f, 0.1f, 0.5f);
+				});
 
-		// 	auto window_2 = app.create_window(600, 600, "OpenGL 2!");
-		// 	comp = window_2->create_component(0, 0.5f, 100, 0.5f);
-		// 	comp->set_background_color(0.2f, 0.5f, 0.3f);
-		// 	auto label = window_2->create_label(50, 50, "Hello World!", {0.5f, 1.0f, 0.5f, 1.0f});
-		// 	label->set_background_color(0.1f, 0.2f, 0.5f);
-		// 	app.run();
-		// }
+				window.create_component(
+					{.x = 0.25f, .y = 50, .width = 0.4f, .height = 150},
+					[](uui::Component& component) { component.set_background_color(0.3f, 0.8f, 0.4f, 0.5f); });
+
+				window.create_label(
+					{.x = 50, .y = 50, .text = "Hello World!", .text_color = {0.5f, 1.0f, 0.5f, 1.0f}},
+					[](uui::Label& label) { label.set_background_color(0.1f, 0.2f, 0.5f, 0.8f); });
+
+				window.create_label({0.5f, 0.5f, "Hello World!", {1.0f, 1.0f, 1.0f, 0.5f}}, [](uui::Label& label) {
+					label.set_background_color(0.5f, 0.5f, 0.1f);
+				});
+				window.create_label({0.75f, 0.75f, "Hello World!", {1.0f, 1.0f, 1.0f, 0.1f}}, {});
+
+				window.create_flex({200, 0.6f, uui::Direction::HORIZONTAL}, [](uui::Flex& flex) {
+					flex.create_component({.width = 100, .height = 50}, [](uui::Component& component) {
+						component.set_background_color(0.2f, 0.75f, 0.25f);
+					});
+					flex.create_label({.text = "test", .text_color = {0.8f, 0.2f, 0.2f, 1.0f}}, {});
+					flex.create_component({100, 20}, [](uui::Component& component) {
+						component.set_background_color(0.2f, 0.25f, 0.75f);
+					});
+				});
+
+				window.create_flex({50, 400, uui::Direction::VERTICAL}, [](uui::Flex& flex) {
+					flex.create_component({50, 100}, [](uui::Component& component) {
+						component.set_background_color(0.2f, 0.75f, 0.25f);
+					});
+					flex.create_label({"test", {0.8f, 0.2f, 0.2f, 1.0f}}, {});
+					flex.create_component({100, 20}, [](uui::Component& component) {
+						component.set_background_color(0.2f, 0.25f, 0.75f);
+					});
+				});
+			});
+
+			app->create_window(800, 600, "OpenGl 2", [](uui::Window& window) {
+				window.create_stack(
+					{.x = 200, .y = 0.6f, .direction = uui::Direction::HORIZONTAL}, [](uui::Stack& stack) {
+						stack.create_component({.width = 100, .height = 50}, [](uui::Component& component) {
+							component.set_background_color(0.2f, 0.75f, 0.25f);
+						});
+						stack.create_label({.text = "test", .text_color = {0.8f, 0.2f, 0.2f, 1.0f}}, {});
+						stack.create_component({.width = 100, .height = 20}, [](uui::Component& component) {
+							component.set_background_color(0.2f, 0.25f, 0.75f);
+						});
+					});
+
+				window.create_stack({.x = 50, .y = 400, .direction = uui::Direction::VERTICAL}, [](uui::Stack& stack) {
+					stack.create_component({.width = 100, .height = 50}, [](uui::Component& component) {
+						component.set_background_color(0.2f, 0.75f, 0.25f);
+					});
+					stack.create_label({.text = "test", .text_color = {0.8f, 0.2f, 0.2f, 1.0f}}, {});
+					stack.create_component({.width = 100, .height = 20}, [](uui::Component& component) {
+						component.set_background_color(0.2f, 0.25f, 0.75f);
+					});
+				});
+			});
+
+			app->run();
+		}
+		cout << "\nStarting example 2" << endl;
+		{
+			auto app = uui::create_application(uui::Application::OPENGL);
+			app->create_window(800, 600, "OpenGl!", [](uui::Window& window) {
+				window.create_component({0.25f, 0.25f, 0.5f, 0.5f}, [](uui::Component& component) {
+					component.set_background_color(0.8f, 0.1f, 0.5f);
+				});
+				window.create_component({0.75f, 0.75f, 0.25f, 0.25f}, [](uui::Component& component) {
+					component.set_background_color(0.2f, 0.1f, 0.5f);
+				});
+			});
+
+			app->create_window(600, 600, "OpenGL 2!", [](uui::Window& window) {
+				window.create_component({0, 0.5f, 100, 0.5f}, [](uui::Component& component) {
+					component.set_background_color(0.2f, 0.5f, 0.3f);
+				});
+				window.create_label({50, 50, "Hello World!", {0.5f, 1.0f, 0.5f, 1.0f}}, [](uui::Label& label) {
+					label.set_background_color(0.1f, 0.2f, 0.5f);
+				});
+			});
+			app->run();
+		}
 	}
 	catch(const std::exception& error)
 	{
diff --git a/src/test/sample.cpp b/src/test/sample.cpp
new file mode 100644
index 0000000..b0d1202
--- /dev/null
+++ b/src/test/sample.cpp
@@ -0,0 +1,15 @@
+#include "uui/uui.hpp"
+
+int main()
+{
+	auto app = uui::create_application(uui::Application::OPENGL);
+	app->create_window(800, 600, "UUI sample", [](uui::Window& window) {
+		window.create_component({.x = 0, .y = 0, .width = 200, .height = 100}, [](uui::Component& component) {
+			component.set_background_color(1.0f, 0.f, 0.f, 0.5f);
+		});
+		window.create_label(
+			{.x = 0.5f, .y = 0.5f, .text = "Hello world!", .text_color = {0.8f, 0.8f, 0.8f, 1.0f}}, nullptr);
+	});
+	app->run();
+	return 0;
+}
diff --git a/src/uui/application.cpp b/src/uui/application.cpp
index 84209ca..368eb79 100644
--- a/src/uui/application.cpp
+++ b/src/uui/application.cpp
@@ -1,3 +1,20 @@
 #include "uui/application.hpp"
 
-bool uui::Application::application_created = false;
+#include <stdexcept>
+
+#include "uui/opengl/application.hpp"
+
+std::shared_ptr<uui::Application> uui::Application::current_application;
+
+std::shared_ptr<uui::Application> uui::create_application(uui::Application::Implementaion implementation)
+{
+	switch(implementation)
+	{
+		case uui::Application::Implementaion::OPENGL:
+			if(uui::Application::current_application != nullptr)
+				throw std::runtime_error("Application error: the application already created");
+			std::shared_ptr<uui::Application> new_application(new uui::GlApplication());
+			uui::Application::current_application = new_application;
+			return new_application;
+	}
+}
diff --git a/src/uui/opengl/application.cpp b/src/uui/opengl/application.cpp
index 79ed9c6..81ceb36 100644
--- a/src/uui/opengl/application.cpp
+++ b/src/uui/opengl/application.cpp
@@ -3,17 +3,35 @@
 #include <chrono>
 #include <iostream>
 
-uui::GlApplication* uui::GlApplication::application_pointer = nullptr;
+#include "uui/opengl/window.hpp"
 
 uui::GlApplication::GlApplication()
 {
-	if(application_pointer != nullptr)
-		throw std::runtime_error("GlApplication error: the application already created");
 	if constexpr(debug_mode)
 		std::cout << "Creating the GlApplication in debug mode" << std::endl;
 	else
 		std::cout << "Creating the GlApplication in release mode" << std::endl;
+	initialized = false;
+
+	init();
+}
+
+uui::GlApplication::~GlApplication()
+{
+	if constexpr(debug_mode)
+		std::cout << "Destroying the GlApplication" << std::endl;
+	if(initialized)
+		deinit();
+}
+
+void uui::GlApplication::init()
+{
+	if constexpr(debug_mode)
+		std::cout << "Initialize the GlApplication" << std::endl;
+
 	// Init GLFW
+	// Avoiding libdecor would be better
+	// glfwInitHint(GLFW_WAYLAND_LIBDECOR, GLFW_WAYLAND_DISABLE_LIBDECOR);
 	glfwInit();
 	// Set all the required options for GLFW
 	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
@@ -23,22 +41,24 @@ uui::GlApplication::GlApplication()
 	if constexpr(uui::GlApplication::debug_mode)
 		glfwWindowHint(GLFW_OPENGL_DEBUG_CONTEXT, true);
 
-	application_pointer = this;
+	initialized = true;
 }
 
-uui::GlApplication::~GlApplication()
+void uui::GlApplication::deinit()
 {
 	if constexpr(debug_mode)
-		std::cout << "Destroying the GlApplication" << std::endl;
+		std::cout << "Deinit the GlApplication" << std::endl;
 	windows.clear();
 	glfwTerminate();
-	application_pointer = nullptr;
+	initialized = false;
 }
 
 void uui::GlApplication::run()
 {
 	if constexpr(debug_mode)
 		std::cout << "Starting the GlApplication" << std::endl;
+	if(!initialized)
+		init();
 
 	auto start_time = std::chrono::high_resolution_clock::now();
 	auto end_time = start_time;
@@ -51,7 +71,7 @@ void uui::GlApplication::run()
 		if constexpr(debug_mode)
 		{
 			end_time = std::chrono::high_resolution_clock::now();
-			render_duration = std::chrono::duration_cast<std::chrono::milliseconds>(end_time - start_time).count();
+			render_duration = std::chrono::duration<float, std::milli>(end_time - start_time).count();
 			// std::cout << "Frame " << frame_count << ", duration: " << render_duration << std::endl;
 			if(frame_count > 0.0f && render_duration > 500.0f)
 			{
@@ -75,6 +95,8 @@ void uui::GlApplication::run()
 					glfwMakeContextCurrent((*(windows.end() - 2))->glfw_window);
 					glfwSwapInterval(1);
 				}
+				if constexpr(debug_mode)
+					std::cout << "\nGlApplication closing GlWindow : " << window->title() << std::endl;
 				window->deinit();
 				windows.erase(it);
 				it -= 1;
@@ -85,7 +107,7 @@ void uui::GlApplication::run()
 					window->render();
 				else
 				{
-					if(window->render_needed && !window->iconified)
+					if(window->_render_needed && !window->_iconified)
 						window->render();
 				}
 			}
@@ -95,11 +117,12 @@ void uui::GlApplication::run()
 	}
 	if constexpr(debug_mode)
 		std::cout << "Ending the GlApplication" << std::endl;
+	current_application = nullptr;
 }
 
-std::shared_ptr<uui::GlWindow> uui::GlApplication::create_window(int width, int height, const std::string& title)
+void uui::GlApplication::create_window(int width, int height, const std::string& title, uui::InitFunction<Window> init)
 {
-	std::shared_ptr<uui::GlWindow> window(new uui::GlWindow(this, windows.size(), width, height, title));
+	auto window = std::shared_ptr<uui::GlWindow>(new uui::GlWindow(current_application, width, height, title));
 	window->init();
 	windows.push_back(window);
 	glfwSwapInterval(1);
@@ -108,10 +131,12 @@ std::shared_ptr<uui::GlWindow> uui::GlApplication::create_window(int width, int
 		glfwMakeContextCurrent((*(windows.end() - 2))->glfw_window);
 		glfwSwapInterval(0);
 	}
-	return window;
+
+	if(window != nullptr && init != nullptr)
+		init(*window);
 }
 
-std::shared_ptr<uui::GlWindow> uui::GlApplication::get_window(size_t index) const
+std::shared_ptr<uui::Window> uui::GlApplication::get_window(std::size_t index) const
 {
 	if(index > windows.size())
 		throw std::runtime_error("Application doesn't have window at given index");
diff --git a/src/uui/opengl/component.cpp b/src/uui/opengl/component.cpp
index 1a43e76..35c1e10 100644
--- a/src/uui/opengl/component.cpp
+++ b/src/uui/opengl/component.cpp
@@ -3,46 +3,62 @@
 #include <iostream>
 
 #include "uui/opengl/application.hpp"
+#include "uui/opengl/container.hpp"
 #include "uui/opengl/gl_utils.hpp"
 
 uui::GlComponent::GlComponent(
-	 std::shared_ptr<GlWindow> window, const std::variant<int, float> x, const std::variant<int, float> y,
-	 const std::variant<int, float> width, const std::variant<int, float> height):
-	 window(window),
-	 position_x(x), position_y(y), size_width(width), size_height(height), initialized(false)
+	std::shared_ptr<uui::GlWindow> window, std::size_t window_index, std::shared_ptr<uui::GlContainer> parent,
+	std::size_t parent_index, const ComponentParams& params)
 {
-	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Creating a GlBox" << std::endl;
+	if constexpr(uui::Application::debug_mode)
+		std::cout << "Creating a GlComponent " << parent_index << std::endl;
 
-	coord_all_relative = true;
-	auto parse_coords = [&](std::variant<int, float>& value) {
+	_type = ComponentType::COMPONENT;
+
+	gl_window = window;
+	this->_window = std::static_pointer_cast<uui::Window>(window);
+	this->_window_index = window_index;
+	this->_parent = std::static_pointer_cast<uui::Container>(parent);
+	this->_parent_index = parent_index;
+
+	_initialized = false;
+
+	_position_x = params.x;
+	_position_y = params.y;
+	_width = params.width;
+	_height = params.height;
+
+	_coord_all_relative = true;
+	auto parse_coords = [&](position_t& value) {
 		if(value.index() == 0)
 		{
 			if(std::get<0>(value) == 0)
 				value = 0.0f;
 			else
-				coord_all_relative = false;
+				_coord_all_relative = false;
 		}
 	};
-	parse_coords(position_x);
-	parse_coords(position_y);
-	parse_coords(size_width);
-	parse_coords(size_height);
+	parse_coords(_position_x);
+	parse_coords(_position_y);
+	parse_coords(_width);
+	parse_coords(_height);
 
-	background_color = {0.0f, 0.0f, 0.0f, 0.0f};
+	_background_color = {0.0f, 0.0f, 0.0f, 0.0f};
 }
 
 uui::GlComponent::~GlComponent()
 {
 	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Closing a GlBox" << std::endl;
-	if(initialized)
+		std::cout << "Destructor GlComponent " << _parent_index << std::endl;
+	if(_initialized)
 		deinit();
+	// if(parent != window)
+	// 	parent->remove_child(0); // TODO
 }
 
 void uui::GlComponent::set_background_color(float r, float g, float b, float a /*=0.0f*/)
 {
-	background_color = {r, g, b, a};
+	_background_color = {r, g, b, a};
 	glBindVertexArray(gl_vao);
 	set_vbo_data();
 	glBindVertexArray(0); // Optional : for safety
@@ -50,8 +66,8 @@ void uui::GlComponent::set_background_color(float r, float g, float b, float a /
 
 void uui::GlComponent::init()
 {
-	if(initialized)
-		throw std::runtime_error("GlBox error : calling init while already initialized");
+	if(_initialized)
+		throw std::runtime_error("GlComponent error : calling init while already initialized");
 
 	glGenVertexArrays(1, &gl_vao);
 	glGenBuffers(1, &gl_vbo);
@@ -64,8 +80,8 @@ void uui::GlComponent::init()
 	set_vbo_data();
 
 	unsigned int indices[] = {
-		 0, 1, 3, // first triangle
-		 1, 2, 3 // second triangle
+		0, 1, 3, // first triangle
+		1, 2, 3 // second triangle
 	};
 	glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, gl_ebo);
 	if constexpr(uui::GlApplication::debug_mode)
@@ -78,65 +94,73 @@ void uui::GlComponent::init()
 	glBindBuffer(GL_ARRAY_BUFFER, 0);
 	glBindVertexArray(0);
 
-	initialized = true;
+	_initialized = true;
 }
 
 void uui::GlComponent::set_vbo_data()
 {
-	float vert_x =
-		 position_x.index() == 1 ? std::get<1>(position_x) : static_cast<float>(std::get<0>(position_x)) / static_cast<float>(window->width);
-	float vert_y =
-		 position_y.index() == 1 ? std::get<1>(position_y) : static_cast<float>(std::get<0>(position_y)) / static_cast<float>(window->height);
-	float vert_w =
-		 size_width.index() == 1 ? std::get<1>(size_width) : static_cast<float>(std::get<0>(size_width)) / static_cast<float>(window->width);
-	float vert_h = size_height.index() == 1 ? std::get<1>(size_height)
-														 : static_cast<float>(std::get<0>(size_height)) / static_cast<float>(window->height);
+	float vert_x = _position_x.index() == 1
+		? std::get<1>(_position_x)
+		: static_cast<float>(std::get<0>(_position_x)) / static_cast<float>(_window->width());
+	float vert_y = _position_y.index() == 1
+		? std::get<1>(_position_y)
+		: static_cast<float>(std::get<0>(_position_y)) / static_cast<float>(_window->height());
+	float vert_w = _width.index() == 1 ? std::get<1>(_width)
+									   : static_cast<float>(std::get<0>(_width)) / static_cast<float>(_window->width());
+	float vert_h = _height.index() == 1
+		? std::get<1>(_height)
+		: static_cast<float>(std::get<0>(_height)) / static_cast<float>(_window->height());
 	float x_min = (2.0f * vert_x) - 1.0f;
 	float x_max = x_min + (2.0f * vert_w);
 	float y_min = (-2.0f * vert_y) + 1.0f;
 	float y_max = y_min - (2.0f * vert_h);
-	std::cout << "Sending vbo data with color: " << background_color[0] << ", " << background_color[1] << ", " << background_color[2] << ", "
-				 << background_color[3] << std::endl;
 	// clang-format off
-	float vertices[] = {
-		x_max, y_min, background_color[0] , background_color[1], background_color[2], background_color[3], // top right
-		x_max, y_max, background_color[0] , background_color[1], background_color[2], background_color[3], // bottom right
-		x_min, y_max, background_color[0] , background_color[1], background_color[2], background_color[3], // bottom left
-		x_min, y_min, background_color[0] , background_color[1], background_color[2], background_color[3]  // top left
+	float vertices[] =
+	{
+		x_max, y_min, _background_color[0], _background_color[1], _background_color[2], _background_color[3],  // top right
+		x_max, y_max, _background_color[0], _background_color[1], _background_color[2], _background_color[3],  // bottom right
+		x_min, y_max, _background_color[0], _background_color[1], _background_color[2], _background_color[3],  // bottom left
+		x_min, y_min, _background_color[0], _background_color[1], _background_color[2], _background_color[3]   // top left
 	};
 	// clang-format on
 	glBindBuffer(GL_ARRAY_BUFFER, gl_vbo);
 	glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
 
 	glVertexAttribPointer(
-		 0, // index
-		 2, // size
-		 GL_FLOAT, // type
-		 GL_FALSE, // enable normalization,
-		 6 * sizeof(float), // stride
-		 (void*)0 // offset
+		0, // index
+		2, // size
+		GL_FLOAT, // type
+		GL_FALSE, // enable normalization,
+		6 * sizeof(float), // stride
+		(void*)0 // offset
 	);
 	glEnableVertexAttribArray(0);
 	glVertexAttribPointer(
-		 1, // index
-		 4, // size
-		 GL_FLOAT, // type
-		 GL_FALSE, // enable normalization,
-		 6 * sizeof(float), // stride
-		 (void*)(2 * sizeof(float)) // offset
+		1, // index
+		4, // size
+		GL_FLOAT, // type
+		GL_FALSE, // enable normalization,
+		6 * sizeof(float), // stride
+		(void*)(2 * sizeof(float)) // offset
 	);
 	glEnableVertexAttribArray(1);
 }
 
 void uui::GlComponent::deinit()
 {
-	if(!initialized)
-		throw std::runtime_error("GlBox error : calling deinit while not initialized");
+	if constexpr(uui::GlApplication::debug_mode)
+		std::cout << "Deinit GlComponent " << _parent_index << std::endl;
+
+	if(!_initialized)
+		throw std::runtime_error("GlComponent error : calling deinit while not initialized");
 
 	glDeleteVertexArrays(1, &gl_vao);
 	glDeleteBuffers(1, &gl_vbo);
 	glDeleteBuffers(1, &gl_ebo);
-	initialized = false;
+
+	_window = nullptr;
+	_parent = nullptr;
+	_initialized = false;
 }
 
 void uui::GlComponent::render()
@@ -147,8 +171,12 @@ void uui::GlComponent::render()
 
 void uui::GlComponent::on_resize()
 {
-	if(!coord_all_relative)
+	bool is_in_stack =
+		_parent != nullptr && (_parent->type() == ComponentType::FLEX || _parent->type() == ComponentType::STACK);
+	if(!_coord_all_relative || is_in_stack)
 	{
+		if(is_in_stack)
+			std::tie(_position_x, _position_y) = _parent->get_child_position(_parent_index);
 		glBindVertexArray(gl_vao);
 		set_vbo_data();
 		glBindVertexArray(0); // Optional : for safety
diff --git a/src/uui/opengl/container_interface.cpp b/src/uui/opengl/container_interface.cpp
new file mode 100644
index 0000000..2abe608
--- /dev/null
+++ b/src/uui/opengl/container_interface.cpp
@@ -0,0 +1,38 @@
+#include "uui/opengl/container_interface.hpp"
+
+#include <iostream>
+
+#include "uui/opengl/component.hpp"
+
+std::size_t uui::GlContainerInterface::push_child(std::shared_ptr<uui::Component> child [[maybe_unused]])
+{
+	throw std::runtime_error("GlContainerInterface error : should only push GlComponent child, not Component");
+}
+
+std::size_t uui::GlContainerInterface::push_child(std::shared_ptr<uui::GlComponent> child)
+{
+	components.push_back(child);
+	return components.size() - 1;
+}
+
+std::shared_ptr<uui::Component> uui::GlContainerInterface::get_child(std::size_t index) const
+{
+	return components.at(index);
+}
+
+void uui::GlContainerInterface::remove_child(std::size_t index)
+{
+	components.at(index) = nullptr;
+};
+
+std::tuple<int, int> uui::GlContainerInterface::get_child_position(const std::size_t child_index [[maybe_unused]]) const
+{
+	return {0, 0};
+}
+
+uui::GlContainerInterface::~GlContainerInterface()
+{
+	if constexpr(uui::Application::debug_mode)
+		std::cout << "Destroying GlContainerInterface" << std::endl;
+	components.clear();
+}
diff --git a/src/uui/opengl/flex.cpp b/src/uui/opengl/flex.cpp
new file mode 100644
index 0000000..e38b6e0
--- /dev/null
+++ b/src/uui/opengl/flex.cpp
@@ -0,0 +1,124 @@
+#include "uui/opengl/flex.hpp"
+
+#include <iostream>
+
+#include "uui/opengl/gl_utils.hpp"
+
+uui::GlFlex::GlFlex(
+	std::shared_ptr<uui::GlWindow> window, std::size_t window_index, std::shared_ptr<uui::GlContainer> parent,
+	std::size_t parent_index, const StackParams& params):
+	GlComponent(window, window_index, parent, parent_index, {params.x, params.y, 0.0f, 0.0f}),
+	GlStack(window, window_index, parent, parent_index, params)
+{
+	if constexpr(uui::GlApplication::debug_mode)
+		std::cout << "Creating a GlFlex " << parent_index << std::endl;
+
+	_type = ComponentType::FLEX;
+
+	_coord_all_relative = false;
+}
+
+std::tuple<int, int> uui::GlFlex::get_child_position(const std::size_t child_index) const
+{
+	const int initial_x = _position_x.index() == 0
+		? std::get<0>(_position_x)
+		: static_cast<int>(std::get<1>(_position_x) * static_cast<float>(_window->width()));
+	const int initial_y = _position_y.index() == 0
+		? std::get<0>(_position_y)
+		: static_cast<int>(std::get<1>(_position_y) * static_cast<float>(_window->height()));
+
+	if(child_index == 0)
+		return {initial_x, initial_y};
+	if(child_index >= components.size())
+		throw std::runtime_error("GlStack error: child_index greater than children count");
+
+	auto get_child_size = [&](std::size_t index) -> std::tuple<int, int> {
+		int width = 0;
+		int height = 0;
+		if(components[index] != nullptr)
+		{
+			auto& component = components[index];
+			if(component->width().index() == 1)
+				width = static_cast<int>(std::get<1>(component->width()) * static_cast<float>(_window->width()));
+			else
+				width = std::get<0>(component->width());
+			if(component->height().index() == 1)
+				height = static_cast<int>(std::get<1>(component->height()) * static_cast<float>(_window->height()));
+			else
+				height = std::get<0>(component->height());
+		}
+		return {width, height};
+	};
+	int x = initial_x;
+	int y = initial_y;
+	if(direction == Direction::HORIZONTAL)
+	{
+		int child_width;
+		int child_height;
+		int max_height = 0;
+
+		std::tie(child_width, child_height) = get_child_size(0);
+		if(child_height > max_height)
+			max_height = child_height;
+		x += child_width;
+		for(std::size_t index = 1; index < child_index; index += 1)
+		{
+			std::tie(child_width, child_height) = get_child_size(index);
+			if(child_height > max_height)
+				max_height = child_height;
+			if(x != initial_x && x + child_width > _window->width())
+			{
+				x = initial_x + child_width;
+				y += max_height;
+				max_height = child_height;
+			}
+			else
+				x += child_width;
+		}
+		if(components[child_index] != nullptr)
+		{
+			std::tie(child_width, child_height) = get_child_size(child_index);
+			if(x != initial_x && x + child_width > _window->width())
+			{
+				x = initial_x;
+				y += max_height;
+			}
+		}
+	}
+	else
+	{
+		int child_width;
+		int child_height;
+		int max_width = 0;
+
+		std::tie(child_width, child_height) = get_child_size(0);
+		if(child_width > max_width)
+			max_width = child_width;
+		y += child_height;
+		for(std::size_t index = 1; index < child_index; index += 1)
+		{
+			std::tie(child_width, child_height) = get_child_size(index);
+			if(child_width > max_width)
+				max_width = child_width;
+			if(y != initial_y && y + child_height > _window->height())
+			{
+				y = initial_y + child_height;
+				x += max_width;
+				max_width = child_width;
+			}
+			else
+				y += child_height;
+		}
+		if(components[child_index] != nullptr)
+		{
+			std::tie(child_width, child_height) = get_child_size(child_index);
+			if(y != initial_y && y + child_height > _window->height())
+			{
+				y = initial_y;
+				x += max_width;
+			}
+		}
+	}
+
+	return {x, y};
+}
diff --git a/src/uui/opengl/font_manager.cpp b/src/uui/opengl/font_manager.cpp
index 546ae6e..18e67f8 100644
--- a/src/uui/opengl/font_manager.cpp
+++ b/src/uui/opengl/font_manager.cpp
@@ -6,12 +6,15 @@
 #include <algorithm>
 #include <iostream>
 
-#include "uui/config.hpp"
 #include "uui/opengl/application.hpp"
 #include "uui/opengl/gl_utils.hpp"
 #include "uui/shader.hpp"
+#include "uui/types.hpp"
 
-uui::GlFontManager::GlFontManager(): initialized(false) {}
+uui::GlFontManager::GlFontManager()
+{
+	initialized = false;
+}
 
 uui::GlFontManager::~GlFontManager()
 {
@@ -25,7 +28,7 @@ void uui::GlFontManager::init()
 		throw std::runtime_error("GlFontManager error : calling init while initialized");
 
 	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Init glFontManager" << std::endl;
+		std::cout << "Init GlFontManager" << std::endl;
 
 	if(FT_Init_FreeType(&ft))
 		throw std::runtime_error("ERROR::FREETYPE: Could not init FreeType Library");
@@ -117,6 +120,9 @@ void uui::GlFontManager::deinit()
 	if(!initialized)
 		throw std::runtime_error("GlFontManager error : calling deinit while not initialized");
 
+	if constexpr(uui::GlApplication::debug_mode)
+		std::cout << "Deinit GlFontManager" << std::endl;
+
 	for(const auto& font: fonts) glDeleteTextures(1, &font.atlas_texture);
 	glDeleteBuffers(1, &gl_vbo);
 	glDeleteBuffers(1, &gl_vao);
@@ -125,7 +131,7 @@ void uui::GlFontManager::deinit()
 	initialized = false;
 }
 
-const uui::GlFontManager::Font& uui::GlFontManager::init_font(const std::string& font_path, size_t font_size)
+const uui::GlFontManager::Font& uui::GlFontManager::init_font(const std::string& font_path, unsigned int font_size)
 {
 	fonts.emplace_back();
 	auto& font = fonts.back();
@@ -167,7 +173,7 @@ const uui::GlFontManager::Font& uui::GlFontManager::init_font(const std::string&
 	glLinkProgram(gl_program);
 
 	// Create a texture that will be used to hold all ASCII glyphs
-	glActiveTexture(Config::FONT_TEXTURE_UNIT);
+	glActiveTexture(GlConfig::FONT_TEXTURE_UNIT);
 	glGenTextures(1, &font.atlas_texture);
 	glBindTexture(GL_TEXTURE_2D, font.atlas_texture);
 
@@ -206,7 +212,8 @@ const uui::GlFontManager::Font& uui::GlFontManager::init_font(const std::string&
 		}
 
 		glTexSubImage2D(
-			 GL_TEXTURE_2D, 0, offset_x, offset_y, glyph->bitmap.width, glyph->bitmap.rows, GL_RED, GL_UNSIGNED_BYTE, glyph->bitmap.buffer);
+			GL_TEXTURE_2D, 0, offset_x, offset_y, glyph->bitmap.width, glyph->bitmap.rows, GL_RED, GL_UNSIGNED_BYTE,
+			glyph->bitmap.buffer);
 		font.char_infos[i].advance_x = glyph->advance.x >> 6;
 		font.char_infos[i].advance_y = glyph->advance.y >> 6;
 
@@ -228,13 +235,13 @@ const uui::GlFontManager::Font& uui::GlFontManager::init_font(const std::string&
 }
 
 std::tuple<int, int> uui::GlFontManager::get_text_size(
-	 const std::string& text, uui::GlFontManager::Font& font, float scale_x, float scale_y)
+	const std::string& text, uui::GlFontManager::Font& font, float scale_x, float scale_y)
 {
 	float width = 0.0f;
 	float height = 0.0f;
 	for(auto current_char: text)
 	{
-		const auto& char_info = font.char_infos[static_cast<size_t>(current_char)];
+		const auto& char_info = font.char_infos[static_cast<std::size_t>(current_char)];
 		width += char_info.advance_x * scale_x;
 		// height = std::max(height, char_info.bitmap_top + char_info.bitmap_height * scale_y);
 		height = std::max(height, roundf(char_info.bitmap_height * scale_y));
@@ -243,14 +250,14 @@ std::tuple<int, int> uui::GlFontManager::get_text_size(
 }
 
 void uui::GlFontManager::render_text(
-	 const std::string& text, uui::GlFontManager::Font& font, float x, float y, float scale_x, float scale_y,
-	 const std::tuple<float, float, float, float>& text_color)
+	const std::string& text, uui::GlFontManager::Font& font, float x, float y, float scale_x, float scale_y,
+	const std::tuple<float, float, float, float>& text_color)
 {
 	GLuint gl_prev_program;
 	glGetIntegerv(GL_CURRENT_PROGRAM, (GLint*)(&gl_prev_program));
 	glUseProgram(gl_program);
 
-	glActiveTexture(Config::FONT_TEXTURE_UNIT);
+	glActiveTexture(GlConfig::FONT_TEXTURE_UNIT);
 	auto [color_r, color_g, color_b, color_a] = text_color;
 	glUniform4f(glGetUniformLocation(gl_program, "textColor"), color_r, color_g, color_b, color_a);
 	glBindVertexArray(gl_vao);
@@ -268,7 +275,7 @@ void uui::GlFontManager::render_text(
 	float out_base_y = y;
 	for(auto current_char: text)
 	{
-		const auto& char_info = font.char_infos[static_cast<size_t>(current_char)];
+		const auto& char_info = font.char_infos[static_cast<std::size_t>(current_char)];
 		//  Calculate the vertex and texture coordinates
 		float char_x = out_base_x + char_info.bitmap_left * scale_x;
 		float char_y = out_base_y - char_info.bitmap_top * scale_y;
@@ -284,15 +291,16 @@ void uui::GlFontManager::render_text(
 			continue;
 
 		// clang-format off
-		float current_vertex[24] = {
-			 char_x, char_y, char_info.texture_x, char_info.texture_y, // top_left
-			 char_x + w, char_y, char_info.texture_x + char_info.bitmap_width / font.atlas_width, char_info.texture_y, // top-right
-			 char_x, char_y + h, char_info.texture_x, char_info.texture_y + char_info.bitmap_height / font.atlas_height, // bottom-right
-			 char_x + w, char_y, char_info.texture_x + char_info.bitmap_width / font.atlas_width, char_info.texture_y, // top-right
-			 char_x, char_y + h, char_info.texture_x, char_info.texture_y + char_info.bitmap_height / font.atlas_height, // bottom-left
-			 char_x + w, char_y + h, char_info.texture_x + char_info.bitmap_width / font.atlas_width,
-			  char_info.texture_y + char_info.bitmap_height / font.atlas_height // bottom-right
-			};
+		float current_vertex[24] =
+		{
+			char_x, char_y, char_info.texture_x, char_info.texture_y, // top_left
+			char_x + w, char_y, char_info.texture_x + char_info.bitmap_width / font.atlas_width, char_info.texture_y, // top-right
+			char_x, char_y + h, char_info.texture_x, char_info.texture_y + char_info.bitmap_height / font.atlas_height, // bottom-right
+			char_x + w, char_y, char_info.texture_x + char_info.bitmap_width / font.atlas_width, char_info.texture_y, // top-right
+			char_x, char_y + h, char_info.texture_x, char_info.texture_y + char_info.bitmap_height / font.atlas_height, // bottom-left
+			char_x + w, char_y + h, char_info.texture_x + char_info.bitmap_width / font.atlas_width,
+			char_info.texture_y + char_info.bitmap_height / font.atlas_height // bottom-right
+		};
 		std::memcpy(vertices.data() + (char_count * 24), current_vertex, 24 * sizeof(float));
 		// clang-format on
 		char_count += 1;
diff --git a/src/uui/opengl/label.cpp b/src/uui/opengl/label.cpp
index 5ba7478..fd16e89 100644
--- a/src/uui/opengl/label.cpp
+++ b/src/uui/opengl/label.cpp
@@ -2,34 +2,39 @@
 
 #include <iostream>
 
+#include "uui/opengl/font_manager.hpp"
 #include "uui/opengl/gl_utils.hpp"
 
 uui::GlLabel::GlLabel(
-	 std::shared_ptr<uui::GlWindow> window, const std::variant<int, float> x, const std::variant<int, float> y, const std::string& text,
-	 const std::tuple<float, float, float, float>& text_color):
-	 GlComponent(window, x, y, 0.0f, 0.0f),
-	 text(text), text_color(text_color)
+	std::shared_ptr<uui::GlWindow> window, std::size_t window_index, std::shared_ptr<uui::GlContainer> parent,
+	std::size_t parent_index, const LabelParams& params):
+	GlComponent(window, window_index, parent, parent_index, {params.x, params.y, 0.0f, 0.0f}), text(params.text),
+	text_color(params.text_color)
 {
-	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Creating a GlLabel" << std::endl;
+	if constexpr(uui::Application::debug_mode)
+		std::cout << "Creating GlLabel " << parent_index << std::endl;
+
+	_type = ComponentType::LABEL;
 
 	font_index = 0;
-	std::tie(text_width, text_height) = window->font_manager.get_text_size(text, window->font_manager.fonts[font_index], 1.0f, 1.0f);
-	size_width = text_width;
-	size_height = text_height;
-	coord_all_relative = false;
+	std::tie(text_width, text_height) =
+		window->font_manager->get_text_size(text, window->font_manager->fonts[font_index], 1.0f, 1.0f);
+	_width = text_width;
+	_height = text_height;
+	_coord_all_relative = false;
 }
 
 void uui::GlLabel::render()
 {
-	float text_x =
-		 position_x.index() == 1 ? std::get<1>(position_x) * static_cast<float>(window->width) : static_cast<float>(std::get<0>(position_x));
-	float text_y =
-		 position_y.index() == 1 ? std::get<1>(position_y) * static_cast<float>(window->height) : static_cast<float>(std::get<0>(position_y));
+	float text_x = _position_x.index() == 1 ? std::get<1>(_position_x) * static_cast<float>(_window->width())
+											: static_cast<float>(std::get<0>(_position_x));
+	float text_y = _position_y.index() == 1 ? std::get<1>(_position_y) * static_cast<float>(_window->height())
+											: static_cast<float>(std::get<0>(_position_y));
 	text_y += static_cast<float>(text_height) - 1;
 
 	glBindVertexArray(gl_vao);
 	glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, (void*)0);
-	window->font_manager.render_text(text.c_str(), window->font_manager.fonts.front(), text_x, text_y, 1.0f, 1.0f, text_color);
+	_window->font_manager->render_text(
+		text.c_str(), _window->font_manager->fonts.front(), text_x, text_y, 1.0f, 1.0f, text_color);
 	glBindVertexArray(0);
 }
diff --git a/src/uui/opengl/stack.cpp b/src/uui/opengl/stack.cpp
new file mode 100644
index 0000000..5fa8862
--- /dev/null
+++ b/src/uui/opengl/stack.cpp
@@ -0,0 +1,101 @@
+#include "uui/opengl/stack.hpp"
+
+#include <iostream>
+
+#include "uui/opengl/gl_utils.hpp"
+#include "uui/opengl/label.hpp"
+
+uui::GlStack::GlStack(
+	std::shared_ptr<uui::GlWindow> window, std::size_t window_index, std::shared_ptr<uui::GlContainer> parent,
+	std::size_t parent_index, const StackParams& params):
+	GlComponent(window, window_index, parent, parent_index, {params.x, params.y, 0.0f, 0.0f})
+{
+	if constexpr(uui::GlApplication::debug_mode)
+		std::cout << "Creating GlStack " << parent_index << std::endl;
+
+	_type = ComponentType::STACK;
+
+	direction = params.direction;
+
+	_coord_all_relative = false;
+}
+
+void uui::GlStack::create_component(const StackComponentParams& params, uui::InitFunction<uui::Component> init)
+{
+	if(!_initialized)
+		throw std::runtime_error("GlWindow error : cannot create component while not initialized");
+
+	glfwMakeContextCurrent(gl_window->glfw_window);
+	std::shared_ptr<uui::GlComponent> component(new uui::GlComponent(
+		gl_window, gl_window->components.size(), std::dynamic_pointer_cast<uui::GlContainer>(shared_from_this()),
+		components.size(), {0, 0, params.width, params.height}));
+	push_child(component);
+	component->init();
+	std::tie(component->_position_x, component->_position_y) = get_child_position(components.size() - 1);
+	gl_window->components.push_back(component);
+
+	if(component != nullptr)
+		init(*component);
+}
+
+void uui::GlStack::create_label(const StackLabelParams& params, uui::InitFunction<uui::Label> init)
+{
+	if(!_initialized)
+		throw std::runtime_error("GlWindow error : cannot create component while not initialized");
+
+	glfwMakeContextCurrent(gl_window->glfw_window);
+	std::shared_ptr<uui::GlLabel> label(new uui::GlLabel(
+		gl_window, gl_window->components.size(), std::dynamic_pointer_cast<uui::GlContainer>(shared_from_this()),
+		components.size(), {0, 0, params.text, params.text_color}));
+	push_child(std::static_pointer_cast<uui::GlComponent>(label));
+	label->init();
+	std::tie(label->_position_x, label->_position_y) = get_child_position(components.size() - 1);
+	gl_window->components.push_back(label);
+
+	if(label != nullptr && init != nullptr)
+		init(*label);
+}
+
+std::tuple<int, int> uui::GlStack::get_child_position(const std::size_t child_index) const
+{
+	int x = _position_x.index() == 0
+		? std::get<0>(_position_x)
+		: static_cast<int>(std::get<1>(_position_x) * static_cast<float>(_window->width()));
+	int y = _position_y.index() == 0
+		? std::get<0>(_position_y)
+		: static_cast<int>(std::get<1>(_position_y) * static_cast<float>(_window->height()));
+
+	if(child_index == 0)
+		return {x, y};
+	if(child_index >= components.size())
+		throw std::runtime_error("GlStack error: child_index greater than children count");
+
+	if(direction == Direction::HORIZONTAL)
+	{
+		for(std::size_t index = 0; index < child_index; index += 1)
+			if(components[index] != nullptr)
+			{
+				auto& component = components[index];
+				if(component->width().index() == 1)
+					x += static_cast<int>(std::get<1>(component->width()) * static_cast<float>(_window->width()));
+				else
+					x += std::get<0>(component->width());
+			}
+	}
+	else
+	{
+		for(std::size_t index = 0; index < child_index; index += 1)
+		{
+			if(components[index] != nullptr)
+			{
+				auto& component = components[index];
+				if(component->height().index() == 1)
+					y += static_cast<int>(std::get<1>(component->height()) * static_cast<float>(_window->height()));
+				else
+					y += std::get<0>(component->height());
+			}
+		}
+	}
+
+	return {x, y};
+}
diff --git a/src/uui/opengl/window.cpp b/src/uui/opengl/window.cpp
index d728d77..a139ba7 100644
--- a/src/uui/opengl/window.cpp
+++ b/src/uui/opengl/window.cpp
@@ -3,12 +3,15 @@
 #include <iostream>
 
 #include "uui/opengl/component.hpp"
+#include "uui/opengl/flex.hpp"
 #include "uui/opengl/gl_utils.hpp"
 #include "uui/opengl/label.hpp"
+#include "uui/opengl/stack.hpp"
 #include "uui/shader.hpp"
 
-static void APIENTRY
-glDebugOutput(GLenum source, GLenum type, unsigned int id, GLenum severity, GLsizei length, const char* message, const void* userParam)
+static void APIENTRY glDebugOutput(
+	GLenum source, GLenum type, unsigned int id, GLenum severity, GLsizei length [[maybe_unused]], const char* message,
+	const void* userParam [[maybe_unused]])
 {
 	// ignore non-significant error/warning codes
 	if(id == 131169 || id == 131185 || id == 131218 || id == 131204)
@@ -57,55 +60,77 @@ void uui::GlWindow::glfw_resize_callback(GLFWwindow* window, int width, int heig
 	glfwMakeContextCurrent(window);
 	auto gl_window = reinterpret_cast<uui::GlWindow*>(glfwGetWindowUserPointer(window));
 	glViewport(0, 0, width, height);
-	gl_window->width = width;
-	gl_window->height = height;
-	gl_window->render_needed = true;
-	gl_window->resize_needed = true;
+	gl_window->_width = width;
+	gl_window->_height = height;
+	gl_window->_render_needed = true;
+	gl_window->_resize_needed = true;
 
 	glm::mat4 projection = glm::ortho(0.0f, static_cast<float>(width), static_cast<float>(height), 0.0f);
 	glfwMakeContextCurrent(window);
-	glUseProgram(gl_window->font_manager.gl_program);
-	glUniformMatrix4fv(glGetUniformLocation(gl_window->font_manager.gl_program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
+	glUseProgram(gl_window->gl_font_manager->gl_program);
+	glUniformMatrix4fv(
+		glGetUniformLocation(gl_window->gl_font_manager->gl_program, "projection"), 1, GL_FALSE,
+		glm::value_ptr(projection));
 }
 
 void uui::GlWindow::glfw_iconify_callback(GLFWwindow* window, int iconified)
 {
 	auto gl_window = reinterpret_cast<uui::GlWindow*>(glfwGetWindowUserPointer(window));
-	gl_window->iconified = iconified;
+	gl_window->_iconified = iconified;
 }
 
-void uui::GlWindow::glfw_key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
+void uui::GlWindow::glfw_key_callback(
+	GLFWwindow* window, int key, int scancode [[maybe_unused]], int action, int mods [[maybe_unused]])
 {
 	if(key == GLFW_KEY_ESCAPE && action == GLFW_PRESS)
 		glfwSetWindowShouldClose(window, true);
 }
 
-uui::GlWindow::GlWindow(uui::GlApplication* app, size_t index, int width, int height, const std::string& title):
-	 app(app), width(width), height(height), render_needed(true), resize_needed(false), iconified(false), index(index), initialized(false)
+// void uui::GlWindow::glfw_mouse_button_callback(GLFWwindow* window, int button, int action, int mods)
+// {
+// 	if (button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS)
+// 	{}
+// }
+
+uui::GlWindow::GlWindow(std::shared_ptr<uui::Application> app, int width, int height, const std::string& title)
 {
-	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Creating a GlWindow" << std::endl;
-	this->title = title;
+	_type = ComponentType::WINDOW;
+
+	_app = app;
+	_initialized = false;
+
+	_title = title;
+	_width = width;
+	_height = height;
+	_render_needed = true;
+	_resize_needed = false;
+	_iconified = false;
+
+	if constexpr(uui::Application::debug_mode)
+		std::cout << "Creating GlWindow : " << title << std::endl;
 }
 
 uui::GlWindow::~GlWindow()
 {
-	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Closing a GlWindow" << std::endl;
-	if(initialized)
+	if constexpr(uui::Application::debug_mode)
+		std::cout << "Destructor GlWindow : " << _title << std::endl;
+	if(_initialized)
 	{
-		if constexpr(uui::GlApplication::debug_mode)
-			std::cout << "Destructor-deinit a GlWindow" << std::endl;
+		if constexpr(uui::Application::debug_mode)
+			std::cout << "Destructor-deinit GlWindow : " << _title << std::endl;
 		deinit();
 	}
 }
 
 void uui::GlWindow::init()
 {
-	if(initialized)
+	if(_initialized)
 		throw std::runtime_error("GlWindow error : calling init while already initialized");
 
-	glfw_window = glfwCreateWindow(width, height, title.c_str(), NULL, NULL);
+	gl_font_manager = std::make_shared<uui::GlFontManager>();
+	font_manager = std::static_pointer_cast<uui::FontManager>(gl_font_manager);
+
+	glfw_window = glfwCreateWindow(_width, _height, _title.c_str(), NULL, NULL);
 	if(glfw_window == NULL)
 		throw std::runtime_error("GLWindow : failed to create GLFW window");
 	glfwMakeContextCurrent(glfw_window);
@@ -201,31 +226,35 @@ void uui::GlWindow::init()
 	glDeleteShader(vertex_shader);
 	glDeleteShader(fragment_shader);
 
-	font_manager.init();
-	glUseProgram(font_manager.gl_program);
-	glm::mat4 projection = glm::ortho(0.0f, static_cast<float>(width), static_cast<float>(height), 0.0f);
-	glUniformMatrix4fv(glGetUniformLocation(font_manager.gl_program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
+	gl_font_manager->init();
+	glUseProgram(gl_font_manager->gl_program);
+	glm::mat4 projection = glm::ortho(0.0f, static_cast<float>(_width), static_cast<float>(_height), 0.0f);
+	glUniformMatrix4fv(
+		glGetUniformLocation(gl_font_manager->gl_program, "projection"), 1, GL_FALSE, glm::value_ptr(projection));
 	glUseProgram(gl_program);
 
-	initialized = true;
+	_initialized = true;
 }
 
 void uui::GlWindow::deinit()
 {
-	if(!initialized)
+	if(!_initialized)
 		throw std::runtime_error("GlWindow error : calling deinit while not initialized");
 
 	if constexpr(uui::GlApplication::debug_mode)
-		std::cout << "Deinit a GlWindow" << std::endl;
+		std::cout << "Deinit GlWindow : " << _title << std::endl;
 
 	glfwMakeContextCurrent(glfw_window);
 	glDeleteProgram(gl_program);
-	for(auto& component: components) component->deinit();
+	for(auto& gl_component: components) gl_component->deinit();
 	components.clear();
-	font_manager.deinit();
+	gl_font_manager->deinit();
 	glfwDestroyWindow(glfw_window);
 
-	initialized = false;
+	_app = nullptr;
+	font_manager = nullptr;
+	gl_font_manager = nullptr;
+	_initialized = false;
 }
 
 void uui::GlWindow::render()
@@ -235,41 +264,69 @@ void uui::GlWindow::render()
 	glClear(GL_COLOR_BUFFER_BIT);
 
 	glUseProgram(gl_program);
-	if(resize_needed)
+	if(_resize_needed)
 	{
 		for(auto& component: components) component->on_resize();
-		resize_needed = false;
+		_resize_needed = false;
 	}
 	for(auto& component: components) component->render();
 	glfwSwapBuffers(glfw_window);
 
-	render_needed = false;
+	_render_needed = false;
 }
 
-std::shared_ptr<uui::GlComponent> uui::GlWindow::create_component(
-	 const std::variant<int, float> x, const std::variant<int, float> y, const std::variant<int, float> width,
-	 const std::variant<int, float> height)
+void uui::GlWindow::create_component(const uui::ComponentParams& params, uui::InitFunction<Component> init)
 {
-	if(!initialized)
+	if(!_initialized)
 		throw std::runtime_error("GlWindow error : cannot create component while not initialized");
 
 	glfwMakeContextCurrent(glfw_window);
-	std::shared_ptr<uui::GlComponent> component(new uui::GlComponent(app->get_window(index), x, y, width, height));
+	std::shared_ptr<uui::GlComponent> component(new uui::GlComponent(shared_from_this(), components.size(), params));
+	push_child(component);
 	component->init();
-	components.push_back(component);
-	return component;
+
+	if(component != nullptr && init != nullptr)
+		init(*component);
 }
 
-std::shared_ptr<uui::GlLabel> uui::GlWindow::create_label(
-	 const std::variant<int, float> x, const std::variant<int, float> y, const std::string& text,
-	 const std::tuple<float, float, float, float>& text_color)
+void uui::GlWindow::create_label(const LabelParams& params, uui::InitFunction<Label> init)
 {
-	if(!initialized)
-		throw std::runtime_error("GlWindow error : cannot create component while not initialized");
+	if(!_initialized)
+		throw std::runtime_error("GlWindow error : cannot create label while not initialized");
 
 	glfwMakeContextCurrent(glfw_window);
-	std::shared_ptr<uui::GlLabel> label(new uui::GlLabel(app->get_window(index), x, y, text, text_color));
+	std::shared_ptr<uui::GlLabel> label(new uui::GlLabel(shared_from_this(), components.size(), params));
+	push_child(std::static_pointer_cast<uui::GlComponent>(label));
 	label->init();
-	components.push_back(label);
-	return label;
+
+	if(label != nullptr && init != nullptr)
+		init(*label);
+}
+
+void uui::GlWindow::create_flex(const StackParams& params, uui::InitFunction<Flex> init)
+{
+	if(!_initialized)
+		throw std::runtime_error("GlWindow error : cannot create flex while not initialized");
+
+	glfwMakeContextCurrent(glfw_window);
+	std::shared_ptr<uui::GlFlex> flex(new uui::GlFlex(shared_from_this(), components.size(), params));
+	push_child(std::static_pointer_cast<uui::GlComponent>(flex));
+	flex->init();
+
+	if(flex != nullptr && init != nullptr)
+		init(*flex);
+}
+
+void uui::GlWindow::create_stack(const StackParams& params, uui::InitFunction<Stack> init)
+{
+	if(!_initialized)
+		throw std::runtime_error("GlWindow error : cannot create stack while not initialized");
+
+	glfwMakeContextCurrent(glfw_window);
+	std::shared_ptr<uui::GlStack> stack(new uui::GlStack(shared_from_this(), components.size(), params));
+	push_child(std::static_pointer_cast<uui::GlComponent>(stack));
+	stack->init();
+
+	if(stack != nullptr && init != nullptr)
+		init(*stack);
 }
diff --git a/src/uui/shader.cpp b/src/uui/shader.cpp
index 2ce9266..ea8e207 100644
--- a/src/uui/shader.cpp
+++ b/src/uui/shader.cpp
@@ -1,7 +1,7 @@
 #include "uui/shader.hpp"
 
 #include <fstream>
-
+#include <ios>
 
 std::vector<char> uui::readFile(const std::string& filename)
 {
@@ -10,10 +10,10 @@ std::vector<char> uui::readFile(const std::string& filename)
 	if(!file.is_open())
 		throw std::runtime_error("failed to open file!");
 
-	size_t fileSize = (size_t)file.tellg();
+	std::size_t fileSize = static_cast<std::size_t>(file.tellg());
 	std::vector<char> buffer(fileSize);
 	file.seekg(0);
-	file.read(buffer.data(), fileSize);
+	file.read(buffer.data(), static_cast<std::streamsize>(fileSize));
 	file.close();
 
 	return buffer;
diff --git a/umake b/umake
index f5965cc..933dea2 160000
--- a/umake
+++ b/umake
@@ -1 +1 @@
-Subproject commit f5965cc91e7eb27d1def78113301e7ec28fad54a
+Subproject commit 933dea2b9e9da0b03489ea9dca3cd597fdd2d09e