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 dear imgui, v1.70 WIP
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 examples/README.txt
 (This is the README file for the examples/ folder. See docs/ for more documentation)
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Dear ImGui is highly portable and only requires a few things to run and render:
 - Providing mouse/keyboard inputs
 - Uploading the font atlas texture into graphics memory
 - Providing a render function to render indexed textured triangles
 - Optional: clipboard support, mouse cursor supports, Windows IME support, etc.
This is essentially what the example bindings in this folder are providing + obligatory portability cruft.
It is important to understand the difference between the core Dear ImGui library (files in the root folder)
and examples bindings which we are describing here (examples/ folder).
You should be able to write bindings for pretty much any platform and any 3D graphics API. With some extra
effort you can even perform the rendering remotely, on a different machine than the one running the logic.
This folder contains two things:
 - Example bindings for popular platforms/graphics API, which you can use as is or adapt for your own use.
 They are the imgui_impl_XXXX files found in the examples/ folder.
 - Example applications (standalone, ready-to-build) using the aforementioned bindings.
 They are the in the XXXX_example/ sub-folders.
You can find binaries of some of those example applications at:
 http://www.dearimgui.org/binaries
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 MISC COMMENTS AND SUGGESTIONS
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 - Please read 'PROGRAMMER GUIDE' in imgui.cpp for notes on how to setup Dear ImGui in your codebase.
 Please read the comments and instruction at the top of each file.
 - If you are using of the backend provided here, so you can copy the imgui_impl_xxx.cpp/h files
 to your project and use them unmodified. Each imgui_impl_xxxx.cpp comes with its own individual
 ChangeLog at the top of the .cpp files, so if you want to update them later it will be easier to
 catch up with what changed.
 - Dear ImGui has 0 to 1 frame of lag for most behaviors, at 60 FPS your experience should be pleasant.
 However, consider that OS mouse cursors are typically drawn through a specific hardware accelerated path
 and will feel smoother than common GPU rendered contents (including Dear ImGui windows).
 You may experiment with the io.MouseDrawCursor flag to request Dear ImGui to draw a mouse cursor itself,
 to visualize the lag between a hardware cursor and a software cursor. However, rendering a mouse cursor
 at 60 FPS will feel slow. It might be beneficial to the user experience to switch to a software rendered
 cursor only when an interactive drag is in progress.
 Note that some setup or GPU drivers are likely to be causing extra lag depending on their settings.
 If you feel that dragging windows feels laggy and you are not sure who to blame: try to build an
 application drawing a shape directly under the mouse cursor.
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 EXAMPLE BINDINGS
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Most the example bindings are split in 2 parts:
 - The "Platform" bindings, in charge of: mouse/keyboard/gamepad inputs, cursor shape, timing, windowing.
 Examples: Windows (imgui_impl_win32.cpp), GLFW (imgui_impl_glfw.cpp), SDL2 (imgui_impl_sdl.cpp)
 - The "Renderer" bindings, in charge of: creating the main font texture, rendering imgui draw data.
 Examples: DirectX11 (imgui_impl_dx11.cpp), GL3 (imgui_impl_opengl3.cpp), Vulkan (imgui_impl_vulkan.cpp)
 - The example _applications_ usually combine 1 platform + 1 renderer binding to create a working program.
 Examples: the example_win32_directx11/ application combines imgui_impl_win32.cpp + imgui_impl_dx11.cpp.
 - Some bindings for higher level frameworks carry both "Platform" and "Renderer" parts in one file.
 This is the case for Allegro 5 (imgui_impl_allegro5.cpp), Marmalade (imgui_impl_marmalade5.cpp).
 - If you use your own engine, you may decide to use some of existing bindings and/or rewrite some using
 your own API. As a recommendation, if you are new to Dear ImGui, try using the existing binding as-is
 first, before moving on to rewrite some of the code. Although it is tempting to rewrite both of the
 imgui_impl_xxxx files to fit under your coding style, consider that it is not necessary!
 In fact, if you are new to Dear ImGui, rewriting them will almost always be harder.
 Example: your engine is built over Windows + DirectX11 but you have your own high-level rendering
 system layered over DirectX11.
 Suggestion: step 1: try using imgui_impl_win32.cpp + imgui_impl_dx11.cpp first.
 Once this work, _if_ you want you can replace the imgui_impl_dx11.cpp code with a custom renderer
 using your own functions, etc.
 Please consider using the bindings to the lower-level platform/graphics API as-is.
 Example: your engine is multi-platform (consoles, phones, etc.), you have high-level systems everywhere.
 Suggestion: step 1: try using a non-portable binding first (e.g. win32 + underlying graphics API)!
 This is counter-intuitive, but this will get you running faster! Once you better understand how imgui
 works and is bound, you can rewrite the code using your own systems.
 - Road-map: Dear ImGui 1.70 (WIP currently in the "viewport" branch) will allows imgui windows to be
 seamlessly detached from the main application window. This is achieved using an extra layer to the
 platform and renderer bindings, which allows imgui to communicate platform-specific requests.
 If you decide to use unmodified imgui_impl_xxxx.cpp files, you will automatically benefit from
 improvements and fixes related to viewports and platform windows without extra work on your side.
List of Platforms Bindings in this repository:
 imgui_impl_glfw.cpp ; GLFW (Windows, macOS, Linux, etc.) http://www.glfw.org/
 imgui_impl_osx.mm ; macOS native API
 imgui_impl_sdl.cpp ; SDL2 (Windows, macOS, Linux, iOS, Android) https://www.libsdl.org
 imgui_impl_win32.cpp ; Win32 native API (Windows)
 imgui_impl_glut.cpp ; GLUT/FreeGLUT (not recommended unless really miss the 90's)
List of Renderer Bindings in this repository:
 imgui_impl_dx9.cpp ; DirectX9
 imgui_impl_dx10.cpp ; DirectX10
 imgui_impl_dx11.cpp ; DirectX11
 imgui_impl_dx12.cpp ; DirectX12
 imgui_impl_metal.mm ; Metal (with ObjC)
 imgui_impl_opengl2.cpp ; OpenGL 2 (legacy, fixed pipeline <- don't use with modern OpenGL context)
 imgui_impl_opengl3.cpp ; OpenGL 3/4, OpenGL ES 2, OpenGL ES 3 (modern programmable pipeline)
 imgui_impl_vulkan.cpp ; Vulkan
List of high-level Frameworks Bindings in this repository: (combine Platform + Renderer)
 imgui_impl_allegro5.cpp
 imgui_impl_marmalade.cpp
Note that Dear ImGui works with Emscripten. 
The examples_emscripten/ app uses sdl.cpp + opengl3.cpp but other combinations are possible.
Third-party framework, graphics API and languages bindings are listed at:
 https://github.com/ocornut/imgui/wiki/Bindings
 Languages: C, C#, ChaiScript, D, Go, Haxe, Java, Lua, Odin, Pascal, PureBasic, Python, Rust, Swift...
 Frameworks: Cinder, Cocoa (OSX), Cocos2d-x, SFML, GML/GameMaker Studio, Irrlicht, Ogre, OpenSceneGraph,
 openFrameworks, LOVE, NanoRT, Nim Game Lib, Qt3d, SFML, Unreal Engine 4...
 Miscellaneous: Software Renderer, RemoteImgui, etc.
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 EXAMPLE APPLICATIONS
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Building:
 Unfortunately in 2018 it is still tedious to create and maintain portable build files using external
 libraries (the kind we're using here to create a window and render 3D triangles) without relying on
 third party software. For most examples here I choose to provide:
 - Makefiles for Linux/OSX
 - Batch files for Visual Studio 2008+
 - A .sln project file for Visual Studio 2010+
 - Xcode project files for the Apple examples
 Please let me know if they don't work with your setup!
 You can probably just import the imgui_impl_xxx.cpp/.h files into your own codebase or compile those
 directly with a command-line compiler.
example_win32_directx9/
 DirectX9 example, Windows only.
 = main.cpp + imgui_impl_win32.cpp + imgui_impl_dx9.cpp
example_win32_directx10/
 DirectX10 example, Windows only.
 = main.cpp + imgui_impl_win32.cpp + imgui_impl_dx10.cpp
example_win32_directx11/
 DirectX11 example, Windows only.
 = main.cpp + imgui_impl_win32.cpp + imgui_impl_dx11.cpp
example_win32_directx12/
 DirectX12 example, Windows only.
 = main.cpp + imgui_impl_win32.cpp + imgui_impl_dx12.cpp
 This is quite long and tedious, because: DirectX12.
example_apple_metal/
 OSX & iOS + Metal.
 = main.m + imgui_impl_osx.mm + imgui_impl_metal.mm
 It is based on the "cross-platform" game template provided with Xcode as of Xcode 9.
 (NB: you may still want to use GLFW or SDL which will also support Windows, Linux along with OSX.)
example_apple_opengl2/
 OSX + OpenGL2.
 = main.mm + imgui_impl_osx.mm + imgui_impl_opengl2.cpp
 (NB: you may still want to use GLFW or SDL which will also support Windows, Linux along with OSX.)
example_empscripten:
 Emcripten + SDL2 + OpenGL3+/ES2/ES3 example.
 = main.cpp + imgui_impl_sdl.cpp + imgui_impl_opengl3.cpp
 Note that other examples based on SDL or GLFW + GL could easily be modified to work with Emscripten.
 We provide this to make the Emscripten differences obvious, and have them not pollute all other examples.
example_glfw_opengl2/
 GLFW + OpenGL2 example (legacy, fixed pipeline).
 = main.cpp + imgui_impl_glfw.cpp + imgui_impl_opengl2.cpp
 **DO NOT USE OPENGL2 CODE IF YOUR CODE/ENGINE IS USING MODERN OPENGL (SHADERS, VBO, VAO, etc.)**
 **Prefer using OPENGL3 code (with gl3w/glew/glad, you can replace the OpenGL function loader)**
 This code is mostly provided as a reference to learn about Dear ImGui integration, because it is shorter.
 If your code is using GL3+ context or any semi modern OpenGL calls, using this renderer is likely to
 make things more complicated, will require your code to reset many OpenGL attributes to their initial
 state, and might confuse your GPU driver. One star, not recommended.
example_glfw_opengl3/
 GLFW (Win32, Mac, Linux) + OpenGL3+/ES2/ES3 example (programmable pipeline).
 = main.cpp + imgui_impl_glfw.cpp + imgui_impl_opengl3.cpp
 This uses more modern OpenGL calls and custom shaders.
 Prefer using that if you are using modern OpenGL in your application (anything with shaders).
example_glfw_vulkan/
 GLFW (Win32, Mac, Linux) + Vulkan example.
 = main.cpp + imgui_impl_glfw.cpp + imgui_impl_vulkan.cpp
 This is quite long and tedious, because: Vulkan.
example_sdl_opengl2/
 SDL2 (Win32, Mac, Linux etc.) + OpenGL example (legacy, fixed pipeline).
 = main.cpp + imgui_impl_sdl.cpp + imgui_impl_opengl2.cpp
 **DO NOT USE OPENGL2 CODE IF YOUR CODE/ENGINE IS USING MODERN OPENGL (SHADERS, VBO, VAO, etc.)**
 **Prefer using OPENGL3 code (with gl3w/glew/glad, you can replace the OpenGL function loader)**
 This code is mostly provided as a reference to learn about Dear ImGui integration, because it is shorter.
 If your code is using GL3+ context or any semi modern OpenGL calls, using this renderer is likely to
 make things more complicated, will require your code to reset many OpenGL attributes to their initial
 state, and might confuse your GPU driver. One star, not recommended.
example_sdl_opengl3/
 SDL2 (Win32, Mac, Linux, etc.) + OpenGL3+/ES2/ES3 example.
 = main.cpp + imgui_impl_sdl.cpp + imgui_impl_opengl3.cpp
 This uses more modern OpenGL calls and custom shaders.
 Prefer using that if you are using modern OpenGL in your application (anything with shaders).
example_sdl_vulkan/
 SDL2 (Win32, Mac, Linux, etc.) + Vulkan example.
 = main.cpp + imgui_impl_sdl.cpp + imgui_impl_vulkan.cpp
 This is quite long and tedious, because: Vulkan.
example_allegro5/
 Allegro 5 example.
 = main.cpp + imgui_impl_allegro5.cpp
example_glut_opengl2/
 GLUT (e.g., FreeGLUT on Linux/Windows, GLUT framework on OSX) + OpenGL2.
 = main.cpp + imgui_impl_glut.cpp + imgui_impl_opengl2.cpp
example_marmalade/
 Marmalade example using IwGx.
 = main.cpp + imgui_impl_marmalade.cpp