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ScuzzBlog: Diaries March 2021

Entry 09th March 2021: Post 1: Amiga Logo - The importance of the Procedure.


Amiga Logo - The importance of the Procedure.
It is easy to forget just how tricky it was for some computers to
generate images in the early days. Today's world of cut and paste
and instant photographs have kinda reduced to a minimum the work
needed in generating artwork. From my own experiences of using
early machines I recall the joy in just joining two lines together.

I spent a good while on the PCW9512 which was a text based word
processor. There were no graphics packages for the computer but
there was CP/M. With the software came a little gem Dr Logo. Many
will know this as turtle graphics as the aim was to use a turtle
on screen to draw patterns and lines.

The software was designed as an educational tool to show kids how
to program and get computers talking to them. My copy of Amiga
Logo even states it is for educational purposes. Whilst the very
simple interface and easy to understand command structure offered
rudimentary controls over the computer, there lurked within quite
a powerful tool with endless possibilities. The 'Procedure'.

The simplistic input tools are all activated by entering commands
after a question mark. So to get the computer to talk or print or
add up it is just a case of inputting a statement after the prompt.
However, to get the little turtle to do its magic you were able
to write sub-programs that were often initiated at the press of a
single key. What was even more interesting was that you could add
all your programs to even bigger programs which in turn could all
initiate other sub programs. And all from a basic 'TO' command.
There are no line numbers just sequential commands that can be
edited and customised at will.

So today I will show you a simple procedure. Nothing heavy but if
you can understand what I did you may then understand how easy it
is to create works of art with the most basic of text based computers.
For my part on the PCW9512 I was able to map images with tracing
sheet and then co-ordinate all lines and nodes/pixels, which I then
transposed to Logo to create pictures. They were quite incredible.

The first image I show today the V1.3 Workbench requester, could
very easily be created from a program like Logo. Remember that
there are no painting tools, no fill tools, no line tools etc. Just 
basicmathematical formula and trigonometry. All command line type
instructions controlling a little turtle.

Amiga Logo - The importance of the Procedure.

A good example of a LOGO style image.

I will use the emulator today. Correct date.

Amiga Logo loaded into 1.3WB.

The 'READ-ME-FIRST'. Old habit.

The mighty Carl Sassenrath and the 'Turtle'.

The turtle ready and waiting.. head first.

You can save and load all your work.

Here is a car. Came with the disk.

Simple commands that direct the
turtle to draw a box.

You can augment the commands to create patterns.

OK I am going to use the 'S C U' in
scuzz to create a sky tractor.

And so to begin the procedure we
say 'TO S' and conclude with END.
From now on when I enter S on the
keyboard, the turtle will draw an S.

Crude but simple. The angle will
vary depending which way the turtle
is pointing. Angles can be described
by telling the turtle to turn say right
and give a number from 0 to 360 degrees.

Time to create the second procedure for
the letter C. Same rules apply.

With U created I can now instruct
the turtle to move from one location
to the next and by simply typing S C U
and returning after each will automatically
create the letters S C U. The joy is that
you can embed the first procedures into a
larger one and then have one just draw all
of the letters SCU at one key press.

Enough of that. Time to have fun.

Look what happens when I change the
C procedure to a different colour
and add a change of direction at the
very end of the procedure. By now typing
in C the computer draws this pattern.

I can then change the colour and
reduce its size just by editing
the procedure. I also created a
new procedure to suit.

Simple stuff but very easy to change
adapt and get that turtle whizzing
around the screen.

And just to finish I then simply
typed C4, S, U, C and created the
bones of my sky tractor. I pressed
just four keys to create the image.

Once you master the maths and start
working with fill commands and line
types etc you can really start and
have some fun.

So save your session and you will
have all your procedures available
to adapt and manipulate to create
bigger and better images.

The extent of tools is quite massive
so it pays to start small and work
your way into the software. This
example only took a few minutes. The
joy in procedures is they are retained
by the program and you can tweak very
gently to get way differing results.

Have fun.


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Last updated 9th March 2021

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