ImGui is a bloat-free graphical user interface library for C++. It outputs vertex buffers that you can render in your 3D-pipeline enabled application. It is portable, renderer agnostic and carries minimal amount of dependencies. It is based on an “immediate” graphical user interface paradigm which allows you to build user interfaces with ease.
ImGui is designed to enable fast iteration and allow programmers to create “content creation” or “debug” tools (as opposed to UI for the average end-user). It favors simplicity and productivity toward this goal, and thus lacks certain features normally found in more high-level libraries.
ImGui is particularly suited to integration in 3D applications, fullscreen applications, embedded applications, games, or any applications on consoles platforms where operating system features are non-standard.
ImGui is self-contained within 6 files that you can easily copy and compile into your application/engine:
Your code passes mouse/keyboard inputs and settings to ImGui (see example applications for more details). After ImGui is setup, you can use it like in this example:
ImGui outputs vertex buffers and simple command-lists that you can render in your application. Because it doesn't know or touch graphics state directly, you can call ImGui commands anywhere in your code (e.g. in the middle of a running algorithm, or in the middle of your own rendering process). Refer to the sample applications in the examples/ folder for instructions on how to integrate ImGui with your existing codebase.
ImGui allows you create elaborate tools as well as very short-lived ones. On the extreme side of short-liveness: using the Edit&Continue feature of compilers you can add a few widgets to tweaks variables while your application is running, and remove the code a minute later! ImGui is not just for tweaking values. You can use it to trace a running algorithm by just emitting text commands. You can use it along with your own reflection data to browse your dataset live. You can use it to expose the internals of a subsystem in your engine, to create a logger, an inspection tool, a profiler, a debugger, etc.
ImGui can load TTF fonts. UTF-8 is supported for text display and input. Here using Arial Unicode font to display Japanese:
The Immediate Mode GUI paradigm may at first appear unusual to some users. This is mainly because “Retained Mode” GUIs have been so widespread and predominant. The following links can give you a better understanding about how Immediate Mode GUIs works.
Where are samples?
The bulk of example user code is contained within the ImGui::ShowTestWindow() function. It covers most features of ImGui so you can read the code and call the function itself to see its output. Ready-to-go example applications covering different versions of OpenGL/DirectX are provided in the examples/ folder.
How do you use ImGui on a platform that may not have a mouse or keyboard?
I recommend using Synergy. With the uSynergy.c micro client running on your platform and connecting to your PC, you can seamlessly use your PC input devices from a video game console or a tablet. ImGui allows to increase the hit box of widgets (via the TouchPadding setting) to accomodate a little for the lack of precision of touch inputs, but it is recommended you use a mouse to allow optimising for screen real-estate.
I integrated ImGui in my engine and the text or lines are blurry..
In your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f).
Can you create elaborate/serious tools with ImGui?
Yes. I have written data browsers, debuggers, profilers and all sort of non-trivial tools with the library. There's no reason you cannot, and in my experience the simplicity of the API is very empowering. However note that ImGui is programmer centric and the immediate-mode GUI paradigm might requires a bit of adaptation before you can realize its full potential.
Is ImGui fast?
Down the fundation of its visual design, ImGui is engineered to be fairly performant both in term of CPU and GPU usage. Running elaborate code and creating elaborate UI will of course have a cost but ImGui aims to minimize it.
Mileage may vary but the following screenshot may give you a rough idea of the cost of running and rendering UI code (In the case of a trivial demo application like this one, your driver/os setup may be a bottleneck and cause higher variation or throttled framerate. Testing performance as part of a real application is recommended).
This is showing framerate for the full application loop on my 2011 iMac running Windows 7, OpenGL, AMD Radeon HD 6700M with an optimized executable. (click here for the full-size picture). In contrast, librairies featuring higher-quality rendering and layouting techniques may have a higher resources footprint.
If you intend to display large lists of items (say, 1000+) it can be beneficial for your code to perform clipping manually - using helpers such as CalcListClipping() - in order to avoid submitting them to ImGui in the first place. Even though ImGui will discard your clipped items it still needs to calculate their size and that overhead will add up if you have thousands of items.
Can you reskin the look of ImGui?
You can alter the look of the interface to some degree: changing colors, sizes, padding, rounding, fonts. However, as ImGui is designed and optimised to create debug tools, the amount of skinning you can apply is limited. There is only so much you can stray away from the default look and feel of the interface.
Why using C++ (as opposed to C)?
ImGui takes advantage of a few C++ features for convenience but nothing anywhere Boost-insanity/quagmire. In particular, function overloading and default parameters are used to make the API easier to use and code more terse. Doing so I believe the API is sitting on a sweet spot and giving up on those features would make the API more cumbersome. Other features such as namespace, constructors and templates (in the case of the ImVector<> class) are also relied on as a convenience but could be removed.
Shall someone wants to use ImGui from another language, it should be possible to wrap ImGui to be used from a raw C API in the future.
Can I donate to support the development of ImGui?
I'm currently an independant developer and your contributions are very meaningful to me. I have setup an ImGui Patreon page if you want to donate and enable me to spend more time improving the library. If your company uses ImGui please consider making a contribution. One-off donations are also greatly appreciated (PayPal link above). I am also available for hire to work on or with ImGui. Thanks!
Developed by Omar Cornut and every direct or indirect contributors to the GitHub. The early version of this library was developed with the support of Media Molecule and first used internally on the game Tearaway.
Embeds ProggyClean.ttf font by Tristan Grimmer (MIT license).
Embeds stb_textedit.h, stb_truetype.h, stb_rectpack.h by Sean Barrett (public domain).
Inspiration, feedback, and testing for early versions: Casey Muratori, Atman Binstock, Mikko Mononen, Emmanuel Briney, Stefan Kamoda, Anton Mikhailov, Matt Willis. And everybody posting feedback, questions and patches on the GitHub.
ImGui is financially supported on Patreon.
And other supporters; thanks!
ImGui is licensed under the MIT License, see LICENSE for more information.