Immediate Mode GUI

Immediate Mode GUI is a GUI where the event processing is directly controlled by the user. The immediate mode GUI widget toolkits are more direct and thus less complex, thus they are a good choice for those who want a simple but easily changeable and extendable GUI toolkit, they are usually generic, open source and cross-platform. The original Immediate Mode GUI toolkit was imgui which is based on OpenGL. There are others such as nuklear with backends for several graphics libraries, or dear imgui written in C++ (here the jvm port).