This set of extensions creates new objects.

This extension generates 3D Polyhedrons. Selecting this extension
pops up a dialog with three tabs. The first tab, *Model
file*, controls the type of polyhedron that is
specified in the *Object* drop-down
menu. If *Load From file* is selected, the
description in the file specified in
the *Filename:* entry box is used. In
the *Object Type* tab you can specify if
the source file describes the object with edges or faces.

The second tab, *View*, allows you to rotate
the polyhedron. Up to six rotations are allowed (for the
mathematicians: why six when
any unique rotation can be specified by only three orthogonal
rotations?).

The third tab, *Style*, allows you to set all
kinds of style parameters, including the *Fill* color and
*opacity*. One can also specify if the faces of the polyhedron
should be shaded to simulate light striking the object. One can
specify the direction from which the light comes. One can
specify if the nodes, edges, or faces should be drawn. And one
can specify if the “hidden” faces should be drawn
(useful if the faces are not fully opaque).

This extension generates exotic-looking text by recombining parts of characters from mostly the Latin alphabet in a way that the original text is discernible. The dialog has entry boxes for the text, scale, and random number seed. Changing the random number seed will change the parts used to generate the text. This effect is based on code written by Matt Chisholm.

This extension generates barcodes. The types of codes that can be generated are:

- EAN8 (European Article Number) 8 digits. A short version of EAN13.
- EAN13 (European Article Number, UPC + 1 digit) 13 digits; one is a checksum. The checksum is calculated.
- UPC-A (Universal Product Code) 12 digits; one is a checksum.
- UPC-E (Universal Product Code) 6 digits; one is a checksum. A compressed representation of UPC-A.
- Code39 (Encodes 26 uppercase letters, 10 digits, and 7 special characters.) Used on packaging.
- Code39Ext (Encodes all 128 ASCII characters.)
- Code93 (Improved version of Code39, used by Canadian Postal Service.)
- Code128 (Encodes all 128 ASCII characters.) Variable length. Includes checksum.
- RM4SCC (Royal Mail 4-state Customer Code, United Kingdom.) Allows letters, numbers, and open/close brackets.

This extension generates calendars. There are a variety of options. One can select a whole year or one month. One can choose Sunday or Monday as the starting day of the week, and one can choose which days are considered to be weekend days. One can choose the colors for the different labels and one can change the default names of the months and the days of the week.

This extension generates Cartesian grids. Options include number of subdivisions, number of sub-subdivisions, linear versus logarithmic divisions, and line widths. For polar coordinates see Polar Grid extension.

This extension is a geometrician's dream. It allows you to create an almost infinite number of constructions based on a triangle. The triangle is defined by the first three nodes in a path (even if the path is not a triangle). The path must be closed and the nodes connected by straight lines.

This extension draws the pattern for a foldable box as one might
use for the input in a desktop cutting plotter (after modifying
the paths). The individual sides and tabs are each represented by
separate paths which are all in a *Group*.

Plot a function versus *x* (horizontal axis). To use, first draw
a rectangle to define the width of the
*x*-axis and the height of the ±1 lines of the
*y*-axis. Then select the extension. In the
pop-up window, enter the *x* and *y* ranges. Checking
the *Multiply x-range by 2π* box
changes the *x*-axis to represent units of 2π, useful for plotting
periodic functions. You can either have the routine
calculate the first derivative of the function numerically
or supply the first derivative yourself.

The function is plotted in the *SVG* coordinate system, which has the
*y*-axis upside down. The extension inserts a minus sign automatically to
correct for this.

All Python math functions are allowed (as
long as they return a single value), including
Python random number functions. The
*Help Tab* has a list of some of the
available functions.

When the *Use polar coordinates* option
is selected, the *x*-range is set to −1 at the left of the
rectangle and +1 at the right side. The *x* values entered
in the extension's dialog are used for the angle
*domain* (in radians). The *Isotropic
scaling* parameter is ignored. *Calculate
first derivative numerically* must also be selected.

Note that depending on the version, Python may return an integer if you divide two integers: thus, 4/5 = 0, while 4.0/5.0 = 0.8.

Draw a realistic mechanical gear. Three
parameters must be given: the *Number of
teeth*, the *Circular pitch* (the
tangential distance between successive teeth), and the
*Pressure angle*. Common values for
*Pressure angle* are: 14.5, 20, and 25
degrees. The radius of the “Pitch Circle” is equal
to N × P/2π, where “N” is the number of teeth and “P” is
the Circular Pitch.

The gear is created around the *SVG* origin and then placed
inside a *Group*. The *Group* is then translated so that the
center of the gear is at the center of the visible canvas. This
makes animating the gear easier as the rotation is then
independent of the displacement. An animated clock using
these gears can be found on the book's
website.

This extension fills the *bounding box* of an object with a grid. The grid
spacing and offset can be independently set in the horizontal and
vertical directions. The grid line width can also be set.

This extension creates *Guide Lines* based on the *Page* size.
One can choose between three *Preset* options.
The first option, *Custom...*, allows one
to create evenly spaced *Guide Lines* with the spacing defined by the
*Vertical guide each* and
*Horizontal guide each* menus. The next
*Preset* option, *Golden
Ratio*, places *Guide Lines* so that the ratios
horizontally or vertically from the *Guide Lines* to the edges
of the page are in proportion to the
*Golden
Ratio* (approximately 1 to 1.62). The
last *Preset* option,
*Rule-of-third*, divides the *Page* horizontally
and vertically into three equal parts. This is equivalent to
using the *Custom...* option with a value
of *1/3*.

Enabling the *Start from edges* option will result
in *Guide Lines* also being created along the *Page* edges.

This extension turns a *LaTeX* string into a path. The string is
typed into a dialog box. The extension requires that Ghostscript,
*LaTeX*, and Pstoedit to be installed and in the execution
path. Pstoedit must include the GNU libplot *SVG* driver or the
shareware *SVG* plug-in,
available for Windows at the Pstoedit website.
The resulting formula is rendered as a path.

An alternative script for Linux using Skencil for the
conversion to *SVG* (avoiding the need for Pstoedit with
*SVG* support) is available at
the book's website: http://tavmjong.free.fr/INKSCAPE/.

Draws *Lindenmayer
System* structures, developed by Aristid
Lindenmayer while studying yeast and fungi growth patterns. It is
beyond the scope of this manual to discuss these structures.
Just one comment: The *Step* parameter controls
the scale of the generated path.

The rules can be very complex. See the Lindenmayer screenshot for more information.

This extension generates parametric curves. It was derived from the Function Plotter extension and shares many of its parameters.

This extension produces a template for a *Perfect-Bound
Cover* as found in *Print On Demand*
services. The template sets the document to the correct size and
creates guides for the front cover, back cover, and spine of the
book, including the specified bleed. The dialog allows for
specifying a variety of parameters including the number of pages
in the book and the thickness of each page. The extension is biased
toward English measurements.

This extension generates polar grids. Options include number of subdivisions, linear versus logarithmic divisions, line widths, and angle labels. For Cartesian coordinates see Cartesian Grid extension.

This extension generates printing marks. Options include
generating
*crop marks*,
*bleed marks*,
*registration marks*,
*star target*,
*color bars*, and
*page information*.
At the moment, the marks are generated “off”
the page. The *Selection* option in the
*Set crop marks to* drop-down menu
in the *Positioning* tab does not
work. You will have to enlarge the *Page* and translate the
drawing with marks after applying this extension. Note that the
printing marks are created on a locked *Layer*
named *Printing Marks*.

Draw a random tree made of straight-line segments. This is a classic from
*Turtle
Geometry*. This implementation is rather limited.

Draw a Spirograph; that is,
an epitrochoid or hypotrochoid curve. Several parameters need to be given:
“R”, the *Ring Radius*;
“r”, the *Gear Radius*; and
“d”, the *Pen Radius*. In addition, one must choose if
the *Gear* travels *Inside* or *Outside*
the *Ring*.
One can also set the *Rotation* angle (the
angle of the starting point relative to the center) and the
*Quality* (roughly, the number of nodes per
loop).

The ratio of “r” to “R” determines the structure of the
curve. Take, for example, an “r” of 36 and an “R” of 48. The ratio
reduced to its simplest form is 3/4. This indicates that the
*Gear* will make a total of four
“loops” as it circles the *Ring*
three times. Simple ratios make simple curves. If you use an
*Even-odd* *fill rule*, the
center of the figure will be unfilled if the denominator is even.

Unlike the case with a real *Spirograph* that
utilizes plastic gears, it is possible to specify values of “r”
and “R” that don't form a *rational
number* ratio. In this case, the curve never
closes on itself and is of infinite length. To avoid such
infinities, the extension limits the number of nodes to 1000. If the
numerator or denominator of the ratio in the simplest form is a
large integer, the *Spirograph* may run out of
nodes. In this case, decreasing the *Quality*
may help.

Also, unlike a “real” Spirograph, the Spirograph
extension allows “d” to be greater than “r”. This results in small
loops along the *Ring*.

This extension generates triangles. Although there are
six parameter entry boxes, only three are used at any one
time. Which three are used is specified in the
*Mode* drop-down menu. Side *c*
is always at the bottom.

*New in v0.48.*

This extension generates a wire frame sphere using ellipses to
represent lines of latitude and longitude. The number of lines
can be specified as well as the orientation of the sphere. An
option allows the removal of *hidden* lines.

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