NAME

       gle - an introduction to the GLE Tubing & Extrusions Library

SYNOPSIS

       #include <GL/gle.h>

DESCRIPTION

       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.

       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.

WEB SITE

       http://linas.org/gle/index.html

SEE ALSO

       gleExtrusion,    gleHelicoid,    gleLathe,    glePolyCone,    glePolyCylinder,   gleScrew,
       gleSetJoinStyle,     gleSpiral,     gleSuperExtrusion,     gleTextureMode,      gleToroid,
       gleTwistExtrusion, gleTwistExtrusion, gleSuperExtrusion

AUTHOR

       Linas Vepstas (linas@linas.org)