Manual Reference Pages - GLE (3)
gle - an introduction to the GLE Tubing & Extrusions Library
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
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.
gleExtrusion, gleHelicoid, gleLathe, glePolyCone, glePolyCylinder,
gleScrew, gleSetJoinStyle, gleSpiral, gleSuperExtrusion, gleTextureMode,
gleToroid, gleTwistExtrusion, gleTwistExtrusion, gleSuperExtrusion
Linas Vepstas (firstname.lastname@example.org)
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