bionic (3) gle.3gle.gz

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)