intro

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
       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@fc.net)




GLE                                   3.6                            gle(3GLE)