Immediate Mode GUI

Compared with the more traditional Retained Mode GUI (RMGUI) such as Qt, MFC, IMGUI is simpler both in terms of usage and implementation. Users don’t need to worry about the data transfer between GUI and the app, don’t even need to write a callback function. The same GUI written with RMGUI would look like this if using IMGUI:

In terms of implementing the library, in RMGUI each widget has their own class, which has members to store corresponding data.

Source: behindthepixels.io