tomato-testing/docs/BACKENDS.md

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Dear ImGui: Backends

The backends/ folder contains backends for popular platforms/graphics API, which you can use in your application or engine to easily integrate Dear ImGui. Each backend is typically self-contained in a pair of files: imgui_impl_XXXX.cpp + imgui_impl_XXXX.h.

• The 'Platform' backends are in charge of: mouse/keyboard/gamepad inputs, cursor shape, timing, and windowing.
  e.g. Windows (imgui_impl_win32.cpp), GLFW (imgui_impl_glfw.cpp), SDL2 (imgui_impl_sdl2.cpp), etc.

• The 'Renderer' backends are in charge of: creating atlas texture, and rendering imgui draw data.
  e.g. DirectX11 (imgui_impl_dx11.cpp), OpenGL/WebGL (imgui_impl_opengl3.cpp), Vulkan (imgui_impl_vulkan.cpp), etc.

• For some high-level frameworks, a single backend usually handles both 'Platform' and 'Renderer' parts.
  e.g. Allegro 5 (imgui_impl_allegro5.cpp). If you end up creating a custom backend for your engine, you may want to do the same.

An application usually combines one Platform backend + one Renderer backend + main Dear ImGui sources. For example, the example_win32_directx11 application combines imgui_impl_win32.cpp + imgui_impl_dx11.cpp. There are 20+ examples in the examples/ folder. See EXAMPLES.MD for details.

Once Dear ImGui is setup and running, run and refer to ImGui::ShowDemoWindow() in imgui_demo.cpp for usage of the end-user API.

What are backends?

Dear ImGui is highly portable and only requires a few things to run and render, typically:

• Required: providing mouse/keyboard inputs (fed into the ImGuiIO structure).
• Required: uploading the font atlas texture into graphics memory.
• Required: rendering indexed textured triangles with a clipping rectangle.

Extra features are opt-in, our backends try to support as many as possible:

• Optional: custom texture binding support.
• Optional: clipboard support.
• Optional: gamepad support.
• Optional: mouse cursor shape support.
• Optional: IME support.
• Optional: multi-viewports support. etc.

This is essentially what each backend is doing + obligatory portability cruft. Using default backends ensure you can get all those features including the ones that would be harder to implement on your side (e.g. multi-viewports support).

It is important to understand the difference between the core Dear ImGui library (files in the root folder) and the backends which we are describing here (backends/ folder).

• Some issues may only be backend or platform specific.
• You should be able to write backends for pretty much any platform and any 3D graphics API. e.g. you can get creative and use software rendering or render remotely on a different machine.

Integrating a backend

See "Getting Started" section of EXAMPLES.MD for more details.

List of backends

In the backends/ folder:

List of Platforms Backends:

imgui_impl_android.cpp    ; Android native app API
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_sdl2.cpp       ; SDL2 (Windows, macOS, Linux, iOS, Android) https://www.libsdl.org
imgui_impl_sdl3.cpp       ; SDL3 (Windows, macOS, Linux, iOS, Android) https://www.libsdl.org (*EXPERIMENTAL UNTIL SDL3 IS RELEASED*)
imgui_impl_win32.cpp      ; Win32 native API (Windows)
imgui_impl_glut.cpp       ; GLUT/FreeGLUT (this is prehistoric software and absolutely not recommended today!)

List of Renderer Backends:

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_sdlrenderer2.cpp ; SDL_Renderer (optional component of SDL2 available from SDL 2.0.18+)
imgui_impl_sdlrenderer3.cpp ; SDL_Renderer (optional component of SDL3 available from SDL 3.0.0+)
imgui_impl_vulkan.cpp     ; Vulkan
imgui_impl_wgpu.cpp       ; WebGPU (web and desktop)

List of high-level Frameworks Backends (combining Platform + Renderer):

imgui_impl_allegro5.cpp

Emscripten is also supported! The SDL+GL, GLFW+GL and GLFW+WebGPU examples are all ready to build and run with Emscripten.

Backends for third-party frameworks, graphics API or other languages

See https://github.com/ocornut/imgui/wiki/Bindings for the full list (e.g. Adventure Game Studio, Cinder, Cocos2d-x, Game Maker Studio2, Godot, LÖVE+LUA, Magnum, Monogame, Ogre, openFrameworks, OpenSceneGraph, SFML, Sokol, Unity, Unreal Engine and many others).

Recommended Backends

If you are not sure which backend to use, the recommended platform/frameworks for portable applications:

Library	Website	Backend	Note
GLFW	https://github.com/glfw/glfw	imgui_impl_glfw.cpp
SDL2	https://www.libsdl.org	imgui_impl_sdl2.cpp
Sokol	https://github.com/floooh/sokol	util/sokol_imgui.h	Lower-level than GLFW/SDL

Using a custom engine?

You will likely be tempted to start by rewrite your own backend using your own custom/high-level facilities...
Think twice!

If you are new to Dear ImGui, first try using the existing backends as-is. You will save lots of time integrating the library. You can LATER decide to rewrite yourself a custom backend if you really need to. In most situations, custom backends have fewer features and more bugs than the standard backends we provide. If you want portability, you can use multiple backends and choose between them either at compile time or at runtime.

Example A: your engine is built over Windows + DirectX11 but you have your own high-level rendering system layered over DirectX11.
Suggestion: try using imgui_impl_win32.cpp + imgui_impl_dx11.cpp first. Once it works, if you really need it, you can replace the imgui_impl_dx11.cpp code with a custom renderer using your own rendering functions, and keep using the standard Win32 code etc.

Example B: your engine runs on Windows, Mac, Linux and uses DirectX11, Metal, and Vulkan respectively.
Suggestion: use multiple generic backends! Once it works, if you really need it, you can replace parts of backends with your own abstractions.

Example C: your engine runs on platforms we can't provide public backends for (e.g. PS4/PS5, Switch), and you have high-level systems everywhere.
Suggestion: try using a non-portable backend first (e.g. win32 + underlying graphics API) to get your desktop builds working first. This will get you running faster and get your acquainted with how Dear ImGui works and is setup. You can then rewrite a custom backend using your own engine API...

Generally: It is unlikely you will add value to your project by creating your own backend.

Also: The multi-viewports feature of the 'docking' branch allows Dear 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 such as: "create an additional OS window", "create a render context", "get the OS position of this window" etc. See 'ImGuiPlatformIO' for details. Supporting the multi-viewports feature correctly using 100% of your own abstractions is more difficult than supporting single-viewport. If you decide to use unmodified imgui_impl_XXXX.cpp files, you can automatically benefit from improvements and fixes related to viewports and platform windows without extra work on your side.