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gle(3GLE)			      GLE			     gle(3GLE)

NAME
       gle - an introduction to the GLE Tubing & Extrusions Library

SYNOPSIS
       #include <GL/tube.h>

DESCRIPTION
       The GLE Tubing and Extrusion Library is a graphics application program‐
       ming interface (API). The library consists of a number of "C"  language
       subroutines  for drawing tubing and extrusions. The library is distrib‐
       uted 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 general‐
       ized 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 arbi‐
       trary 2D contour to be swept around an arbitrary 3D path. A set of nor‐
       mal  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	shear‐
       ing 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, gle‐
       Screw, gleSetJoinStyle, gleSpiral,  gleSuperExtrusion,  gleTextureMode,
       gleToroid, gleTwistExtrusion, gleTwistExtrusion, gleSuperExtrusion

AUTHOR
       Linas Vepstas (linas@fc.net)

GLE				      3.6			     gle(3GLE)
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