IUP (software)

The IUP Portable User Interface is a computer software development kit that provides a portable, scriptable toolkit to build graphical user interfaces (GUIs) using the programming languages C, Perl, Lua and Nim, among others. This allows rapid, zero-compile prototyping and refinement of deployable GUI applications.

Original author(s)Tecgraf/PUC-Rio in collaboration with Petrobras
Stable release
3.28 / 13 December 2019 (2019-12-13)
Operating systemCross-platform
TypeSoftware development kit

IUP's purpose is to allow programs user interface to run in different systems in unmodified form.[1]

It provides this ability by binding Lua with its C/C++ code, or simply writing C to the application programming interface (API). It handles user interface elements by using native controls provided by native APIs, such as Windows API in Windows, GTK+ in Linux, and Motif-LessTif in older Unices. It also provides some custom developed controls using graphics APIs such as CD - Canvas Draw or OpenGL.


IUP's distinguishing features include:

  • ANSI C API, one of the few plain C-capable toolkits,
  • Single API for Windows or Linux,
  • Built in support for Lua scripts calling IUP functions (controlled by Lua script),
  • Removal of the restriction of class/instance object types, but retaining the prototype Lua-style hierarchy of inheritance.
  • An abstract layout model, in which sizes and positions are calculated from horizontal and vertical containers, rather than explicit X and Y coordinates. Coordinate-based layout is also supported with a third container type.
  • Small API, on the order of about 100 functions.
  • Use of an event loop-callback mechanism. This main loop can be called inside Lua.
  • Interface elements are created before they are mapped to the native elements. This is the reverse of the usual situation for assembling GUI elements.
  • Available as source or pre-built static or dynamic libraries for wide variety of compilers, including turnkey example source.

The Lua scripting is done by binding Lua and IUPLua in (at least) a small C program called a host application. This program creates a Lua state, passes the Lua state to IUPLua for initialization, and then opens and executes a Lua script against the Lua state. Or, the entire IUP state can be dynamically loaded via use of a Lua require or package.loadlib of IUPLua.

The script(s) can later be compiled with the Lua compiler if needed.

Support for UTF-8 was added to the Windows target in November 2013 with the release of version 3.9.

IUP is liberally-licensed for free use, modification, sale, and redistribution under the MIT license.[2]

IUP has been in development at least since the 1.8 version issued in 1998. It was begun in collaboration with Petrobras.


  1. "IUP - Portable User Interface". www.tecgraf.puc-rio.br. Retrieved 2016-09-24.
  2. "Tecgraf Library License". www.tecgraf.puc-rio.br. Retrieved 2015-12-03.

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