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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