Graphics Environment for Multimedia
Graphics Environment for Multimedia (GEM) is a set of externals (libraries) that provide OpenGL graphics functionality to Pure Data, a graphical programming language for real-time audio processing. It is free under the GNU General Public License (GPL). Originally written by Mark Danks of Sony Computer Entertainment, it is now maintained by Johannes Zmölnig of the Institute of Electronic Music and Acoustics. It was once (but is no longer) partly supported by a grant from the Intel Research Council for The Global Visual Music project of Vibeke Sorensen, Miller Puckette and Rand Steiger. The externals provide support for many objects, such as polygon graphics, lighting, texture mapping, image processing, and camera motion. See also 
 Pure Data
 OpenGL

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C++ libraries
Widget toolkits
Free software programmed in C++
Audio software for Linux