Add project files.

vendor/imgui/include/imgui_impl_opengl3.h

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+// dear imgui: Renderer Backend for modern OpenGL with shaders / programmatic pipeline
+// - Desktop GL: 2.x 3.x 4.x
+// - Embedded GL: ES 2.0 (WebGL 1.0), ES 3.0 (WebGL 2.0)
+// This needs to be used along with a Platform Backend (e.g. GLFW, SDL, Win32, custom..)
+
+// Implemented features:
+//  [X] Renderer: User texture binding. Use 'GLuint' OpenGL texture identifier as void*/ImTextureID. Read the FAQ about ImTextureID!
+//  [x] Renderer: Desktop GL only: Support for large meshes (64k+ vertices) with 16-bit indices.
+
+// You can copy and use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
+// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
+// Read online: https://github.com/ocornut/imgui/tree/master/docs
+
+// About Desktop OpenGL function loaders:
+//  Modern Desktop OpenGL doesn't have a standard portable header file to load OpenGL function pointers.
+//  Helper libraries are often used for this purpose! Here we are supporting a few common ones (gl3w, glew, glad).
+//  You may use another loader/header of your choice (glext, glLoadGen, etc.), or chose to manually implement your own.
+
+// About GLSL version:
+//  The 'glsl_version' initialization parameter should be NULL (default) or a "#version XXX" string.
+//  On computer platform the GLSL version default to "#version 130". On OpenGL ES 3 platform it defaults to "#version 300 es"
+//  Only override if your GL version doesn't handle this GLSL version. See GLSL version table at the top of imgui_impl_opengl3.cpp.
+
+#pragma once
+#include "imgui.h"      // IMGUI_IMPL_API
+
+// Backend API
+IMGUI_IMPL_API bool     ImGui_ImplOpenGL3_Init(const char* glsl_version = NULL);
+IMGUI_IMPL_API void     ImGui_ImplOpenGL3_Shutdown();
+IMGUI_IMPL_API void     ImGui_ImplOpenGL3_NewFrame();
+IMGUI_IMPL_API void     ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data);
+
+// (Optional) Called by Init/NewFrame/Shutdown
+IMGUI_IMPL_API bool     ImGui_ImplOpenGL3_CreateFontsTexture();
+IMGUI_IMPL_API void     ImGui_ImplOpenGL3_DestroyFontsTexture();
+IMGUI_IMPL_API bool     ImGui_ImplOpenGL3_CreateDeviceObjects();
+IMGUI_IMPL_API void     ImGui_ImplOpenGL3_DestroyDeviceObjects();
+
+// Specific OpenGL ES versions
+//#define IMGUI_IMPL_OPENGL_ES2     // Auto-detected on Emscripten
+//#define IMGUI_IMPL_OPENGL_ES3     // Auto-detected on iOS/Android
+
+// Attempt to auto-detect the default Desktop GL loader based on available header files.
+// If auto-detection fails or doesn't select the same GL loader file as used by your application,
+// you are likely to get a crash in ImGui_ImplOpenGL3_Init().
+// You can explicitly select a loader by using one of the '#define IMGUI_IMPL_OPENGL_LOADER_XXX' in imconfig.h or compiler command-line.
+#if !defined(IMGUI_IMPL_OPENGL_ES2) \
+ && !defined(IMGUI_IMPL_OPENGL_ES3) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_GL3W) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_GLEW) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_GLAD) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_GLAD2) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_GLBINDING2) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_GLBINDING3) \
+ && !defined(IMGUI_IMPL_OPENGL_LOADER_CUSTOM)
+
+// Try to detect GLES on matching platforms
+#if defined(__APPLE__)
+#include "TargetConditionals.h"
+#endif
+#if (defined(__APPLE__) && (TARGET_OS_IOS || TARGET_OS_TV)) || (defined(__ANDROID__))
+#define IMGUI_IMPL_OPENGL_ES3               // iOS, Android  -> GL ES 3, "#version 300 es"
+#elif defined(__EMSCRIPTEN__)
+#define IMGUI_IMPL_OPENGL_ES2               // Emscripten    -> GL ES 2, "#version 100"
+
+// Otherwise try to detect supported Desktop OpenGL loaders..
+#elif defined(__has_include)
+#if __has_include(<GL/glew.h>)
+    #define IMGUI_IMPL_OPENGL_LOADER_GLEW
+#elif __has_include(<glad/glad.h>)
+    #define IMGUI_IMPL_OPENGL_LOADER_GLAD
+#elif __has_include(<glad/gl.h>)
+    #define IMGUI_IMPL_OPENGL_LOADER_GLAD2
+#elif __has_include(<GL/gl3w.h>)
+    #define IMGUI_IMPL_OPENGL_LOADER_GL3W
+#elif __has_include(<glbinding/glbinding.h>)
+    #define IMGUI_IMPL_OPENGL_LOADER_GLBINDING3
+#elif __has_include(<glbinding/Binding.h>)
+    #define IMGUI_IMPL_OPENGL_LOADER_GLBINDING2
+#else
+    #error "Cannot detect OpenGL loader!"
+#endif
+#else
+    #define IMGUI_IMPL_OPENGL_LOADER_GL3W   // Default to GL3W embedded in our repository
+#endif
+
+#endif

vendor/imgui/include/imgui_impl_sdl.h

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+// dear imgui: Platform Backend for SDL2
+// This needs to be used along with a Renderer (e.g. DirectX11, OpenGL3, Vulkan..)
+// (Info: SDL2 is a cross-platform general purpose library for handling windows, inputs, graphics context creation, etc.)
+
+// Implemented features:
+//  [X] Platform: Mouse cursor shape and visibility. Disable with 'io.ConfigFlags |= ImGuiConfigFlags_NoMouseCursorChange'.
+//  [X] Platform: Clipboard support.
+//  [X] Platform: Keyboard arrays indexed using SDL_SCANCODE_* codes, e.g. ImGui::IsKeyPressed(SDL_SCANCODE_SPACE).
+//  [X] Platform: Gamepad support. Enabled with 'io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad'.
+// Missing features:
+//  [ ] Platform: SDL2 handling of IME under Windows appears to be broken and it explicitly disable the regular Windows IME. You can restore Windows IME by compiling SDL with SDL_DISABLE_WINDOWS_IME.
+
+// You can copy and use unmodified imgui_impl_* files in your project. See examples/ folder for examples of using this.
+// If you are new to Dear ImGui, read documentation from the docs/ folder + read the top of imgui.cpp.
+// Read online: https://github.com/ocornut/imgui/tree/master/docs
+
+#pragma once
+#include "imgui.h"      // IMGUI_IMPL_API
+
+struct SDL_Window;
+typedef union SDL_Event SDL_Event;
+
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForOpenGL(SDL_Window* window, void* sdl_gl_context);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForVulkan(SDL_Window* window);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForD3D(SDL_Window* window);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_InitForMetal(SDL_Window* window);
+IMGUI_IMPL_API void     ImGui_ImplSDL2_Shutdown();
+IMGUI_IMPL_API void     ImGui_ImplSDL2_NewFrame(SDL_Window* window);
+IMGUI_IMPL_API bool     ImGui_ImplSDL2_ProcessEvent(const SDL_Event* event);

vendor/imgui/include/imgui_sdl.h

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+#pragma once
+
+struct ImDrawData;
+struct SDL_Renderer;
+
+namespace ImGuiSDL
+{
+	// Call this to initialize the SDL renderer device that is internally used by the renderer.
+	void Initialize(SDL_Renderer* renderer, int windowWidth, int windowHeight);
+	// Call this before destroying your SDL renderer or ImGui to ensure that proper cleanup is done. This doesn't do anything critically important though,
+	// so if you're fine with small memory leaks at the end of your application, you can even omit this.
+	void Deinitialize();
+
+	// Call this every frame after ImGui::Render with ImGui::GetDrawData(). This will use the SDL_Renderer provided to the interfrace with Initialize
+	// to draw the contents of the draw data to the screen.
+	void Render(ImDrawData* drawData);
+}