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. 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 known to run on UNIX(r) and UNIX-like operating systems such as Linux, AIX, IRIX, Ultrix and HPUX with OpenGL or Mesa. GLE is also known to run on OS/2 Warp.

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

The End

Version 1.0 -- Originally developed by Linas Vepstas 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 -- 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