# GLE Tubing and Extrusion Fact Sheet

## The Hard Facts

The GLE Tubing and Extrusion Library is a graphics application programming interface (API). The library consists of a number of "C" language subroutines for drawing tubing and extrusions. It is a very fast implementation of these shapes, outperforming all other implementations, most by orders of magnitude. The library is distributed in source code form, in a package that includes documentation, a VRML proposal, Makefiles, and full source code and header files. It uses the OpenGL (TM) programming API to perform the actual drawing of the tubing and extrusions.

GLE is designed for and maintained on the Linux operating system, and is known to run on other Unix operating systems such as AIX, IRIX, Ultrix and HPUX with OpenGL or Mesa. GLE is also known to run on IBM OS/2 Warp, Apple Macintosh OS9, and Microsoft Windows NT and has been used to develop screen-savers for some of these popular PC operating systems.

News: Alpha Blending/Transparency now supported by means of new `*_c4f` routines that allow RGBA values to be passed down into the API.

News: Dave Richards has created a set of MSWindows-specific C++ classes that are derived from gle. See the GLE32 site. (mirror)

News: There is now a mailing list to discuss gle: `gle-discuss@lists.sourceforge.net`. Subscribe by web or view the archives.

News: Version 3.0 is out, sporting an improved/simplified build system, which should make compiling this package a lot less confusing. Project has been moved to SourceForge, which means you can get live CVS, and should make it easier for folks to submit patches & participate in this project.

News: ShapeShifter is a re-write of the GLE library in Java. Available freely, under the 'Artistic License'.

News: OpenGL internals programmers & hardware developers, please read this.

News: Python bindings are shipped with this release. They were generated with a non-standard version of SWIG. There is also another (different) set of bindings for GLE that come standard with OpenGL at the PyOpenGL site. At this point, neither set should be considered to be more 'standard' than the other.

## A Gentle Introduction

The libgle.a library contains a collection of routines for drawing sweeps and extrusions. A "sweep" or "extrusion" is a 2D contour (polyline) that is swept or extruded along a 3D path (polyline). For example, sweeping a circle along a straight line will generate a cylinder. Sweeping a circle along a circular path will generate a doughnut (torus).

The library also includes a set of utility routines for drawing some of the more common extruded shapes: a polycylinder, a polycone, a generalized torus (circle swept along a helical path), a "helix" (arbitrary contour swept along a helical path) and a "lathe" (arbitrary contour swept along a helical path, with torsion used to keep the contour aligned).

The most general extrusion supported by this library allows an arbitrary 2D contour to be swept around an arbitrary 3D path. A set of normal vectors can be specified to go along with the contour; the normal vectors determine the appearance of the contour when lighting is turned on. A set of colors and affine matrices can be specified to go along with the 3D path. The colors are used to color along the path. The affine matrices are used to operate on the contour as it is swept along. If no affine matrices are specified, the contour is extruded using the mathematical concept of "parallel translation" or "Gaussian translation". That is, the contour is moved (and drawn) along the extrusion path in a "straight" manner. If there are affine matrices, they are applied to the contour at each extrusion segment before the segment is drawn.

The affine matrices allow work in a quasi-non-Euclidean space. They essentially allow the contour to be distorted as it is swept along. The allow the contour to be rotated, translated and rescaled as it is drawn. For example, a rescaling will turn a polycylinder into a poly-cone, since the circle that is being extruded is scaled to a different size at each extrusion vertex. A rotation allows the contour to be spun around while it is being extruded, thus for instance allowing drill-bit type shapes to be drawn. A translation allows the appearance of shearing in real space; that is, taking a contour and displacing it, without otherwise bending it. Note that the affines are 2x3 matrices, not 3x4 matrices, since they apply to the 2D contour as it is being extruded.

## Table of Contents

- Tubing & Extrusions Subroutine Documentation
- JoinStyle Subroutine Documentation
- Texture Generation
- Compiling the Library
- Design & Implementation Internals, the Pipeline
- A VRML Extension Proposal
- The GLE Web Site
- GLE on SourceForge (live CVS)
- The GLE LSM entry
- Source Code Distribution (Primary -- linas.org)
- Source Code Distribution (Secondary -- Metalab)
- Source Code Distribution (Secondary -- TSX-11)

## Version Summary

Version 1.0 -- Originally developed by Linas Vepstas for IBM GL 3.2 and SGI IrisGL in 1991
Version 2.0 -- Port to OpenGL, March, July, October 1993
Version 2.1 -- Port demos to GLUT Library, assorted lint/compile time cleanup, April 1995
Version 2.1.1 -- Additional demos, October 1995
Version 2.2.0 -- Fully HTML'ized documentation, Christmas 1995
Version 2.2.1 -- Additional demos
Version 2.2.2 -- Extensive screen shots added to documentation, January 1996
Version 2.2.3 -- VRML proposal, February 1996
Version 2.2.4 -- metalab (prev. sunsite), tsx-11 post, March 1996
Version 2.2.5 -- Documentation cleanup, July 1996
Version 2.2.6 -- Documentation cleanup, April 1997
Version 2.2.7 -- Minor bug fixes, December 1997
Version 2.3 -- Bug fixes for drawing of end caps for MesaGL, man pages from Mark Kilgard, December 1997
Version 3.0.0 -- Consolidation, simplification of build structure; major version number changed because header files consolidated and renamed. Use automake/autoconf to build. Move CVStree to sourceforge. June 2000
Version 3.0.1 -- Misc bug fixes, configure.in fix
Version 3.0.2 -- C++ wrapper fixes
Version 3.0.3 -- look for libXmu in configure
Version 3.0.4 -- python bindings, minor bug fix
Version 3.0.5 -- Visual C project files; create pipeline documentation; fix makefile to install docs, examples.
Version 3.0.6 -- disable fprintf(stderr) on Win32 systems. use newer automake/autoconf configure. Add GPL as an alternate license choice. November 2001.
Version 3.0.7 -- configure.in libXi fix for detecting libglut.
Version 3.0.8 -- configure.in check for libXi first ... Fix memory leak with atexit()
Version 3.1.0 -- Add support for Alpha Blending -- March 2003

## Credits

Written and maintained by Linas Vepstas <linas@linas.org>.
Many thanks Mark Kilgard for converting the web pages to real Unix man pages.
Visit my Enterprise Linux web site for more info about Linux in a commercial, business setting.