IFS

By R. S. Doiel, 2020-05-02

This is a port of the IFS module described in Martin Reiser and Niklaus Wirth's "Programming in Oberon: Steps beyond Pascal and Modula-2". The code has been adapted from the original Oberon presented in the book to Oberon-7 as described in Wirth's Project Oberon 2013.

Requirements

• A POSIX computer system
• A Text editor
• OBNC v0.16.1
  • A "C" tool chain
  • libsdl2

Source Code organization

One module file and several data files are included in this project.

• IFS.Mod is a port of the original described in the book
• Data files: Barnsley Fern, Variation on Barnsley Fern, Sierpinski Triangle and Square.

Compilation

    obnc IFS.Mod

The data file format

The module's Init* procedure needs to read in the initialization data before drawing the fractals. The data file format is as follows

Map of values

The initialization procedures reads text from standard input. The layout of variables is as follows.

x0 y0 e
a1 a2 a3 a4
b1 b2 b3 b4
c1 c2 c3 c4
d1 d2 d3 d4
e1 e2 e3 e4
f1 f2 f3 f4
p1 p2 p3 p4

Row Integers

x0  y0  e

x0 and y0 are the left and bottom edges. e is the a scaling factor. In the source it is referred to as "unit size".

Rows 2 through 8 are Reals

The remaining rows are real number values. Each column represents a function pass (e.g. 1 to 4). Each rows represents a variable, a, b, c, d, e, f, p values.

In all rows numbers are separated by one or more spaces.

Barnsley Fern:

440  28    64
0.0  0.85  0.2  -0.15
0.0  0.04  -0.26 0.28
0.0  -0.04 0.23  0.26
0.16 0.85  0.22  0.24
0.0  0.0   0.0   0.0
0.0  1.60  1.60  0.44
0.01 0.85  0.07  0.07  

Fractal Tree

480    1      1200
0.0    0.42   0.42   0.1
0.0    -0.42  0.42   0.0
0.0    0.42   -0.42  0.0
0.5    0.42   0.42   0.1
0.0    0.0    0.0    0.0
0.0    0.2    0.2    0.2
0.05   0.4    0.4    0.15

Running IFS

    ./IFS < Fern1.txt
    ./IFS < Tree.txt

The program expects to read a series of integer and real values from standard input. You can use a POSIX style pipe or redirect to cause IFS to read the file.

In Closing

This code was originally developed by Martin Reiser and Niklaus Wirth as part of their 1992 book, "Programming in Oberon: Steps beyond Pascal and Modula-2"¹. This repository was an exercise and seeing how easy it would be to adapt the book's code to Oberon-7.

Footnotes