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 dear imgui, v1.80 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 backends 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 backends which we are describing here (examples/ folder).
You should be able to write backends 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 backends 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 backends.
   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


---------------------------------------
 GETTING STARTED
---------------------------------------

 - 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.
   Please read FAQ at http://www.dearimgui.org/faq

 - If you are using of the backend provided here, you can add 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 no particular extra lag for most behaviors, e.g. the value of 'io.MousePos' provided in
   NewFrame() will result at the time of EndFrame()/Render() in a moved windows rendered following that mouse
   movement. At 60 FPS your experience should be pleasant.
   However, consider that OS mouse cursors are typically drawn through a very specific hardware accelerated
   path and will feel smoother than the majority of contents rendererd via regular graphics API (including,
   but not limited to Dear ImGui windows). Because UI rendering and interaction happens on the same plane as
   the mouse, that disconnect may be jarring to particularly sensitive users.
   You may experiment with enabling the io.MouseDrawCursor flag to request Dear ImGui to draw a mouse cursor
   using the regular graphics API, to help you visualize the difference between a "hardware" cursor and a
   regularly rendered software cursor.
   However, rendering a mouse cursor at 60 FPS will feel sluggish so you likely won't want to enable that at
   all times. It might be beneficial for 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 display lag depending on their settings.
   If you feel that dragging windows feels laggy and you are not sure what the cause is: try to build a simple
   drawing a flat 2D shape directly under the mouse cursor.


---------------------------------------
 EXAMPLE BACKENDS
---------------------------------------

Most the example backends are split in 2 parts:

 - The "Platform" backends, 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), etc.

 - The "Renderer" backends, 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), etc.

 - The example _applications_ usually combine 1 platform + 1 renderer backend to create a working program.
   Examples: the example_win32_directx11/ application combines imgui_impl_win32.cpp + imgui_impl_dx11.cpp.

 - Some backends 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 backends and/or rewrite some using
   your own API. As a recommendation, if you are new to Dear ImGui, try using the existing backend 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 backends 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 backend 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 1.80 (WIP currently in the "docking" 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 backends, which allows Dear 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 Backends in this repository:

    imgui_impl_glfw.cpp       ; GLFW (Windows, macOS, Linux, etc.) http://www.glfw.org/
    imgui_impl_osx.mm         ; macOS native API (not as feature complete as glfw/sdl backends)
    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 (absolutely not recommended in 2020!)

List of Renderer Backends 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 Backends 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 imgui_impl_sdl.cpp and
imgui_impl_opengl3.cpp, but other combinations are possible.

Third-party framework, graphics API and languages backends are listed at:

    https://github.com/ocornut/imgui/wiki/Bindings

Including backends for:

    AGS/Adventure Game Studio, Amethyst, bsf, Cinder, Cocos2d-x, Diligent Engine, Flexium,
    GML/Game Maker Studio2, GTK3+OpenGL3, Irrlicht Engine, LÖVE+LUA, Magnum, NanoRT, Nim Game Lib,
    Ogre, openFrameworks, OSG/OpenSceneGraph, Orx, px_render, Qt/QtDirect3D, SFML, Sokol,
    Unreal Engine 4, vtk, Win32 GDI, etc.

Not sure which to use?
Recommended platform/frameworks:

    GLFW    https://github.com/glfw/glfw        Use imgui_impl_glfw.cpp
    SDL2    https://www.libsdl.org              Use imgui_impl_sdl.cpp
    Sokol   https://github.com/floooh/sokol     Use util/sokol_imgui.h in Sokol repository.

Those will allow you to create portable applications and will solve and abstract away many issues.


---------------------------------------
 EXAMPLE APPLICATIONS
---------------------------------------

Building:
  Unfortunately in 2020 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 we choose to provide:
   - Makefiles for Linux/OSX
   - Batch files for Visual Studio 2008+
   - A .sln project file for Visual Studio 2012+
   - Xcode project files for the Apple examples
  Please let us 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.

  If you are interested in using Cmake to build and links examples, see:
    https://github.com/ocornut/imgui/pull/1713 and https://github.com/ocornut/imgui/pull/3027


example_allegro5/
    Allegro 5 example.
    = main.cpp + imgui_impl_allegro5.cpp

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: imgui_impl_osx.mm is currently not as feature complete as other platforms backends.
    You may prefer to use the GLFW Or SDL backends, which will also support Windows and Linux.)

example_apple_opengl2/
    OSX + OpenGL2.
    = main.mm + imgui_impl_osx.mm + imgui_impl_opengl2.cpp
    (NB: imgui_impl_osx.mm is currently not as feature complete as other platforms backends.
    You may prefer to use the GLFW Or SDL backends, which will also support Windows and Linux.)

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 + OpenGL 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_metal/
    GLFW (Mac) + Metal example.
    = main.mm + imgui_impl_glfw.cpp + imgui_impl_metal.mm

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/glad2/glbinding, 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).
    (Please be mindful that accessing OpenGL3+ functions requires a function loader, which are a frequent
    source for confusion for new users. We use a loader in imgui_impl_opengl3.cpp which may be different
    from the one your app normally use. Read imgui_impl_opengl3.h for details and how to change it.)

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.
    For this example, the main.cpp file exceptionally use helpers function from imgui_impl_vulkan.h/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
    Note that GLUT/FreeGLUT is largely obsolete software, prefer using GLFW or SDL.

example_marmalade/
    Marmalade example using IwGx.
    = main.cpp + imgui_impl_marmalade.cpp

example_null
    Null example, compile and link imgui, create context, run headless with no inputs and no graphics output.
    = main.cpp
    This is used to quickly test compilation of core imgui files in as many setups as possible.
    Because this application doesn't create a window nor a graphic context, there's no graphics output.

example_sdl_directx11/
    SDL2 + DirectX11 example, Windows only.
    = main.cpp + imgui_impl_sdl.cpp + imgui_impl_dx11.cpp
    This to demonstrate usage of DirectX with SDL.

example_sdl_metal/
    SDL2 (Mac) + Metal example.
    = main.mm + imgui_impl_sdl.cpp + imgui_impl_metal.mm

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/glad2/glbinding, 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).
    (Please be mindful that accessing OpenGL3+ functions requires a function loader, which are a frequent
    source for confusion for new users. We use a loader in imgui_impl_opengl3.cpp which may be different
    from the one your app normally use. Read imgui_impl_opengl3.h for details and how to change it.)

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.
    For this example, the main.cpp file exceptionally use helpers function from imgui_impl_vulkan.h/cpp.

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.