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)