VPython 5.50: the extrusion object

At vpython.org are installers for VPython 5.50 which include a
powerful new "extrusion" object developed by Kadir Haldenbilen and me.
The basic idea is that you prepare a 2D shape which you then extrude
along a path that is like the pos attribute of a curve object:

    extrusion(pos=...., shape=....)

Libraries of common shapes and paths are provided (rectangle, circle,
arc, star, etc.). Included are tools for creating complex gears, and
shapes made from text.

The 2D shape can be prepared using "constructive geometry" supported
by the Polygon module (which is imported by VPython and included with
the Windows and Mac installers). Polygon objects consist of closed
contours (lists of points in the xy plane), and these objects can be
combined. For example, if R is a Polygon object representing a
rectangle, and C is a Polygon object representing a circle that lies
within the boundary of the rectangle, then R-C is a 2D shape
consisting of a rectangle with a hole in it, which can be extruded
along a path by using the extrusion object. If the circle lies partly
outside the rectangle, R-C is a rectangle with a portion of a circle
cut out of the edge.

The implementation of the extrusion object is quite fast and
efficient, so that not only is it easy to create quite complex
objects, but it is also feasible to make the object change dynamically
by altering the path, the scale factors along the path, the amount of
twist along the path, or even the extruded shape.

After installing VPython 5.50, you are encouraged to run the new
example program

      extrusion_overview.py

which is an interactive tutorial on the extrusion object and also an
interesting demonstration of the tutorial possibilities of VPython.

Kadir Haldenbilen has contributed new example programs
electric_motor.py (the program which produced the attached image),
differential_gear.py, conch.py, medusa.py, and extruded_columns.py
that illustrate some uses of the new extrusion object. He has also
contributed some useful new materials: shiny, chrome, blazed, silver,
bricks, ice, glass, and BlueMarble (earth with clouds), and the
example program material_test.py has been revised to display all the
materials now available.

The text object now uses the extrusion object for its display, but the
extrusion object does not make the text object obsolete, because the
text object emphasizes text-related information such as line widths,
etc. The shapes.text() routine supplies the necessary information to
the text object, and this additional information can be used by you
should you wish to do so.

The curve object has been updated to permit using paths obtained from
the new paths library.

For the benefit of Linux users who might not have installed the
Polygon, FontTools, and ttfquery modules that are needed by the 3D
text object and by the new extrusion object, the imports have been
rearranged in such a way that if you don’t have the necessary modules
installed you can still run VPython, but without being able to use
text and extrusion objects.

A long-standing bug has been fixed in keyboard handling on the Mac, in
which each keypress generated two events, the first one correct and
the second one garbage.
The tutorial program extrusion_overview.py made it clear that the
default font height of 13 of label text was not actually consistent
across Windows, Mac, and Linux. The text has been adjusted so that
labels look quite similar on all platforms.

Bruce Sherwood

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