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142 lines
8.3 KiB
Markdown
_(You may browse this at https://github.com/ocornut/imgui/blob/master/docs/BACKENDS.md or view this file with any Markdown viewer)_
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## Dear ImGui: Backends
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**The backends/ folder contains backends for popular platforms/graphics API, which you can use in
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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.
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- The 'Platform' backends are in charge of: mouse/keyboard/gamepad inputs, cursor shape, timing, windowing.<BR>
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e.g. Windows ([imgui_impl_win32.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_win32.cpp)), GLFW ([imgui_impl_glfw.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_glfw.cpp)), SDL2 ([imgui_impl_sdl.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_sdl.cpp)), etc.
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- The 'Renderer' backends are in charge of: creating atlas texture, rendering imgui draw data.<BR>
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e.g. DirectX11 ([imgui_impl_dx11.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_dx11.cpp)), OpenGL/WebGL ([imgui_impl_opengl3.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_opengl3.cpp), Vulkan ([imgui_impl_vulkan.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_vulkan.cpp), etc.
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- For some high-level frameworks, a single backend usually handle both 'Platform' and 'Renderer' parts.<BR>
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e.g. Allegro 5 ([imgui_impl_allegro5.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_allegro5.cpp)), Marmalade ([imgui_impl_marmalade.cpp](https://github.com/ocornut/imgui/blob/master/backends/imgui_impl_marmalade.cpp)). If you end up creating a custom backend for your engine, you may want to do the same.
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An application usually combines 1 Platform backend + 1 Renderer backend + main Dear ImGui sources.
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For example, the [example_win32_directx11](https://github.com/ocornut/imgui/tree/master/examples/example_win32_directx11) application combines imgui_impl_win32.cpp + imgui_impl_dx11.cpp. There are 20+ examples in the [examples/](https://github.com/ocornut/imgui/blob/master/examples/) folder. See [EXAMPLES.MD](https://github.com/ocornut/imgui/blob/master/docs/EXAMPLES.md) for details.
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**Once Dear ImGui is setup and running, run and refer to `ImGui::ShowDemoWindow()` in imgui_demo.cpp for usage of the end-user API.**
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### What are backends
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Dear ImGui is highly portable and only requires a few things to run and render, typically:
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- Required: providing mouse/keyboard inputs (fed into the `ImGuiIO` structure).
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- Required: uploading the font atlas texture into graphics memory.
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- Required: rendering indexed textured triangles with a clipping rectangle.
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Extra features are opt-in, our backends try to support as many as possible:
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- Optional: custom texture binding support.
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- Optional: clipboard support.
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- Optional: gamepad support.
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- Optional: mouse cursor shape support.
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- Optional: IME support.
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- Optional: multi-viewports support.
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etc.
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This is essentially what each backends are 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).
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It is important to understand the difference between the core Dear ImGui library (files in the root folder)
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and backends which we are describing here (backends/ folder).
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- Some issues may only be backend or platform specific.
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- You should be able to write backends for pretty much any platform and any 3D graphics API.
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e.g. you can get creative and use software rendering or render remotely on a different machine.
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### Integrating a backend
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See "Getting Started" section of [EXAMPLES.MD](https://github.com/ocornut/imgui/blob/master/docs/EXAMPLES.md) for more details.
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### List of backends
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In the [backends/](https://github.com/ocornut/imgui/blob/master/backends) folder:
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List of Platforms Backends:
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imgui_impl_android.cpp ; Android native app API
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imgui_impl_glfw.cpp ; GLFW (Windows, macOS, Linux, etc.) http://www.glfw.org/
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imgui_impl_osx.mm ; macOS native API (not as feature complete as glfw/sdl backends)
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imgui_impl_sdl.cpp ; SDL2 (Windows, macOS, Linux, iOS, Android) https://www.libsdl.org
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imgui_impl_win32.cpp ; Win32 native API (Windows)
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imgui_impl_glut.cpp ; GLUT/FreeGLUT (this is prehistoric software and absolutely not recommended today!)
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List of Renderer Backends:
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imgui_impl_dx9.cpp ; DirectX9
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imgui_impl_dx10.cpp ; DirectX10
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imgui_impl_dx11.cpp ; DirectX11
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imgui_impl_dx12.cpp ; DirectX12
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imgui_impl_metal.mm ; Metal (with ObjC)
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imgui_impl_opengl2.cpp ; OpenGL 2 (legacy, fixed pipeline <- don't use with modern OpenGL context)
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imgui_impl_opengl3.cpp ; OpenGL 3/4, OpenGL ES 2, OpenGL ES 3 (modern programmable pipeline)
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imgui_impl_vulkan.cpp ; Vulkan
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imgui_impl_wgpu.cpp ; WebGPU
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List of high-level Frameworks Backends (combining Platform + Renderer):
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imgui_impl_allegro5.cpp
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imgui_impl_marmalade.cpp
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Emscripten is also supported.
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The [example_emscripten_opengl3](https://github.com/ocornut/imgui/tree/master/examples/example_emscripten_opengl3) app uses imgui_impl_sdl.cpp + imgui_impl_opengl3.cpp, but other combos are possible.
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### Backends for third-party frameworks, graphics API or other languages
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See https://github.com/ocornut/imgui/wiki/Bindings for the full list.
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### Recommended Backends
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If you are not sure which backend to use, the recommended platform/frameworks for portable applications:
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|Library |Website |Backend |Note |
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|--------|--------|--------|-----|
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| GLFW | https://github.com/glfw/glfw | imgui_impl_glfw.cpp | |
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| SDL2 | https://www.libsdl.org | imgui_impl_sdl.cpp | |
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| Sokol | https://github.com/floooh/sokol | [util/sokol_imgui.h](https://github.com/floooh/sokol/blob/master/util/sokol_imgui.h) | Lower-level than GLFW/SDL |
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### Using a custom engine?
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You will likely be tempted to start by rewrite your own backend using your own custom/high-level facilities...<BR>
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Think twice!
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If you are new to Dear ImGui, first try using the existing backends as-is.
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You will save lots of time integrating the library.
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You can LATER decide to rewrite yourself a custom backend if you really need to.
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In most situations, custom backends have less features and more bugs than the standard backends we provide.
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If you want portability, you can use multiple backends and choose between them either at compile time
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or at runtime.
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**Example A**: your engine is built over Windows + DirectX11 but you have your own high-level rendering
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system layered over DirectX11.<BR>
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Suggestion: try using imgui_impl_win32.cpp + imgui_impl_dx11.cpp first.
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Once it works, if you really need it you can replace the imgui_impl_dx11.cpp code with a
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custom renderer using your own rendering functions, and keep using the standard Win32 code etc.
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**Example B**: your engine runs on Windows, Mac, Linux and uses DirectX11, Metal, Vulkan respectively.<BR>
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Suggestion: use multiple generic backends!
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Once it works, if you really need it you can replace parts of backends with your own abstractions.
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**Example C**: your engine runs on platforms we can't provide public backends for (e.g. PS4/PS5, Switch),
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and you have high-level systems everywhere.<BR>
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Suggestion: try using a non-portable backend first (e.g. win32 + underlying graphics API) to get
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your desktop builds working first. This will get you running faster and get your acquainted with
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how Dear ImGui works and is setup. You can then rewrite a custom backend using your own engine API.
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Also:
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The [multi-viewports feature](https://github.com/ocornut/imgui/issues/1542) of the 'docking' branch allows
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Dear ImGui windows to be seamlessly detached from the main application window. This is achieved using an
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extra layer to the Platform and Renderer backends, which allows Dear ImGui to communicate platform-specific
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requests such as: "create an additional OS window", "create a render context", "get the OS position of this
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window" etc. See 'ImGuiPlatformIO' for details.
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Supporting the multi-viewports feature correctly using 100% of your own abstractions is more difficult
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than supporting single-viewport.
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If you decide to use unmodified imgui_impl_XXXX.cpp files, you can automatically benefit from
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improvements and fixes related to viewports and platform windows without extra work on your side.
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