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Fractal Workshop
The Mandelbrot/Julia set generator for the ST
(c)1992 Conrad Bessant
e-mail: ppyhcmb@uk.ac.nott.vax
NB: It is recommended that you print out this file for reference - it is only
four pages long.
Fractal Workshop comprises the following files:
FRACTAL.PRG Fractal Workshop 1.5a program
FRACTAL.DOC Fractal Workshop 1.5a documentation
BOOK.DOC Information about a related book for the ST
*.PI3 Example files for high resolution monochrome monitors
*.PI1 Example files for low resolution colour monitors
Fractal Workshop is public domain. It may be freely distributed on the
condition that all the above files are included in their original form.
Where space is a limited (on bulletin boards for example) the *.PI? example
files may be omitted.
No part of Fractal Workshop may be sold for profit or incorporated in a
commercial product without prior written permission from Conrad Bessant.
This software is supplied 'as is' without warranty of any kind either express
or implied. Conrad Bessant accepts no responsibility for any legal or other
consequences which may arise directly or indirectly as a result of the use
of all or parts of Fractal Workshop.
Starting Fractal Workshop
-------------------------
Simply click on the FRACTAL.PRG icon.
Summary
-------
The Mandelbrot set is now the recognised logo of chaos theory, and there are
many programs around which will render colourful Mandelbrot images on the ST.
Fractal Workshop provides all the standard Mandelbrot plotting and zooming
facilities, with additional display options. A vast number of Julia sets may
also be created with this program.
The program's main features are:
o Fast generation of the Mandelbrot set or a Julia set with user-defined
complex constant
o Support for colour and monochrome monitors
o Several plotting methods; colour (low resolution mode only) or monochrome
with optional external and internal structure
o Zoom facility with automatic aspect ratio preservation and iteration
ceiling calculation
o Filing of fractals to disk in Degas compatible format
o Optional user-defined iteration ceiling
o Display of mathematical constants when relevant
Most of the menu options will be disabled (shown in light text) when the
program is loaded because there is no image on the screen to manipulate.
Before continuing it is therefore necessary to get a Mandelbrot or Julia set
onto the screen. This can be done either by plotting a new set from scratch
or by loading a previously drawn one.
Plotting a Mandelbrot or Julia set
----------------------------------
The similarities between Mandelbrot and Julia sets made it seem eminently
sensible to integrate the two fractals into one program. This has had the
effect of making many actions, such as file manipulation and zooming in, the
same for both fractals.
Before plotting a set you should first select the way in which the set's
structure is to be drawn, using the Structure menu. The four options are:
o mono: the set will be rendered in alternate black and white contours
o colour: each pixel will be plotted in a colour representing the number of
iterations required to free that point from the 'Mandelbrot circle'
o external structure: dwell bands will appear around the fractal when this
option is ticked, if it is not ticked the area around the fractal will
be plain white
o internal structure: bands will be drawn inside the fractal when this is
ticked, if it is not ticked the inside of the fractal will be plotted
in black
Note that the mono and colour menu options are mutually exclusive, but any
combination of the other two options is allowed.
The default settings in this menu are for a 'traditional' Mandelbrot set:
For colour systems; mono: off, colour: on, external: on, internal: off.
For mono systems; mono: on, colour: disabled, external: on, internal: off.
Plotting a Mandelbrot set
-------------------------
Once the plotting method has been selected the Plot Mandelbrot option of the
Picture menu can be used to plot the set. Before plotting begins a dialogue
window will appear in the bottom left corner of the screen informing you of
the range of x and y and prompting you to enter the iteration ceiling. Unless
you know what these values mean you should just hit <Return> to accept the
default values. The program will then start plotting the set, for the whole
set this will take about 10 minutes (40 minutes on high resolution monitors
because more points are plotted). Plotting can be abandoned by holding down
the right mouse button.
Plotting a Julia set
--------------------
Plotting a Julia set is very similar to plotting a Mandelbrot set except that
Plot Julia set... should be selected from the Picture menu instead of the
Mandelbrot equivalent. Because there are an infinite number of Julia sets
compared to the single Mandelbrot set it is also necessary to select the
required set when choosing the Julia menu option. This is done by entering
the real and imaginary parts of the complex constant associated with the
required set. This constant is entered in the dialogue window which appears
immediately after selecting Plot Julia set... from the Picture menu.
You can use any constant you like, but the values for both parts of the
constant must be between -2 and +2. Good values for the constant can be found
in chaos books, the following examples are taken from 'Computers and Chaos:
Atari ST Edition':
Real part Imaginary Part
-1.16 -0.25
0.32 0.04
-1.25 -0.01
0.00 -1.00
After selecting the constant a dialogue window will appear, reminding you of
the constant and prompting you for the iteration ceiling. As before, it's
advisable to just press <Return> at this point to commence plotting. A Julia
set will usually take slightly less time to plot than a Mandelbrot set
(possibly only five minutes low resolution colour mode).
Zooming in
----------
The method of magnifying a section of a set (i.e. zooming in) is identical for
Mandelbrot and Julia sets.
Firstly the Zoom in option should be selected from the Picture menu, you will
then be prompted to select the section to magnify using the mouse. You can
only magnify rectangular sections, so you must first move to the top left
corner of the rectangle which you wish the enlarge. When at this position you
should press and HOLD DOWN the left mouse button, dragging out the resulting
rectangle until it encloses the desired area. Once the rectangle is
satisfactorily placed the left mouse button should be released. If, during
dragging, you are not satisfied with the rectangle the right mouse button
should be pressed to cancel the operation while you are still holding down
the left button - the rectangle will then disappear. Once the rectangle has
been selected a dialogue window will appear showing the newly selected ranges
of x and y, and suggesting an automatically calculated iteration ceiling
(based on the one that was used for the previous plot).
You are given the chance to edit this ceiling, after which the new section of
the set will start being plotted.
Notes:
o It is possible to change the selections made in the Structure menu
before zooming in - if you are zooming into a fractal that you have just
loaded this may be especially useful as the plotting method is not saved
as part of the fractal file
o It is possible to zoom into a plot of an enlarged section
o Note that it is possible to halt plotting (by holding down the right hand
mouse button) and then zoom into the unfinished plot
Printing
--------
Printing is only possible if you have copied a Degas compatible printer driver
into the root directory of the disk on which Fractal Workshop is stored. No
such drivers are supplied on the disk, so initially the Print option will be
disabled order the produce screen dumps you should copy the relevant routine
for your printer into the root directory of your disk. Fractal Workshop will
then automatically find this file and the Print option will be enabled. If
you are unfamiliar with the form of Degas printer drivers, they are exactly
2000 bytes in length and have filenames ending in .PRT (e.g. EPSON.PRT). A
selection can be found on the disk supplied with the Degas package and others
are available in the public domain.
File operations
---------------
Once plotted a Mandelbrot or Julia set can easily be saved to disk by
selecting the Save option from the File menu and then entering the relevant
file name (and directory path if necessary) in the file selector. The files
are stored in a Degas compatible format, so it is possible to load them into
most commercial graphics, animation DTP programs.
If the file currently on display already exists on disk a tick will be shown
next to the Save option in the File menu. This helps to prevent accidental
loss of plots and multiple saves.
A fractal saved from Fractal Workshop can be loaded up at a later date using
the option of the File menu. A file selector will appear in which the
relevant filename should be be clicked on. Note that normal Degas pictures
(ie. those not created with Fractal Workshop) cannot be loaded into Fractal
Workshop.
The File menu also contains an option to delete files from disk, which is
useful if you run out of disk space but desperately want to save a file.