What Is ImGui? Dear ImGui Explained

What is ImGui?

ImGui, short for Dear ImGui, is a small immediate-mode GUI library for C++. It draws a menu fresh every frame from plain function calls instead of keeping a tree of widget objects around. That makes it fast to wire up and easy to drop on top of a game's existing render loop, which is why tooling and native clients use it for low-latency overlays.

The key insight is "immediate-mode": instead of creating a Button object and storing it, you call a function that says "draw a button here," and that call both draws the button and tells you whether it was clicked this frame.

What immediate-mode means

ImGui rebuilds the interface on every frame. You do not create a button object and store it. You call a function that says "draw a button here," and that call both draws the button and tells you whether it was clicked this frame.

A retained-mode toolkit works the other way. It keeps a long-lived widget tree in memory, and you update that tree when state changes. Immediate-mode trades that persistent structure for code that reads top to bottom and lives next to your own state.

1. Application runs frame loop

   The game renders a frame and calls the UI code as part of it.

2. UI code runs

   You call ImGui functions to build the menu from top to bottom: buttons, sliders, checkboxes.

3. ImGui draws and responds

   The functions both render the widgets and return whether they were interacted with this frame.

4. Your code reacts

   You read the return values and update your own state, like calling do_thing() when the button was clicked this frame.

Why tools and clients pick it

ImGui is popular for menus that sit over a 3D scene. The reasons are practical:

• Low latency: it hooks into a frame the program already renders, so the menu reacts right away.
• Little glue: a window and a few controls are a handful of function calls. There is no layout file and no separate UI thread to manage.
• Self-contained: the library has few dependencies and slots into common graphics backends, so it doesn't pull in a heavy framework.
• Debug-friendly: the same calls that build a release menu also build the throwaway debug panels developers use while building a feature.

Immediate-mode vs retained-mode

Immediate-mode is ideal for something that needs to update every frame and respond to input instantly. Retained-mode is better for something that sits mostly static and changes rarely.

How it fits a native client

A native utility client built in C++ often draws its menu with ImGui over the game's frame. The menu code runs inside the render loop, reads the client's own settings, and writes changes straight back. There's no separate UI process, so toggling a feature is one function call against a value the client already owns.

This is a C++ pattern. A Fabric mod written in Java reaches its interface through the game's own GUI hooks instead, so ImGui mostly shows up in clients that ship as native code rather than as Java mods.

FAQ