Monthly Display - December 2017


Vic-20 Graphics

Back in my October monthly display (about Branching Fractals), I started with some early images that I produced on the Commodore Vic-20 computer that I had in 1989. When looking back at those images, and some other images produced using the Vic-20, I realised that there were enough interesting images to present in a monthly display.


320 x 352 pixels, produced on a Vic-20 computer, using my own machine code graphics routines, and manual editing of pixels.


I remember my father buying a Commodore Vic-20 computer back in 1981, and plugging it into the family TV to see what it was all about. He had been reading about these 'inexpensive' personal computers ($350 back then was still a lot of money) and with a keen interest in electronics, he wanted to learn how to program one, and thought that it would be good for his children to explore as well. I remember the first time the Vic-20 was turned on, it came up with a display as below, saying "CBM BASIC V2", "3583 BYTES FREE", and "READY.", with a flashing blue block.

The unexpanded Vic-20 greeting screen on startup. Note the number of bytes available for entering and running a program.

Not knowing what to do next, we consulted a manual that came with the computer. The Vic-20 came with a connected data cassette player that allowed the user to load and save programs. The Vic-20's operating system contained prompts that helped users to do what they wanted. The computer seemed to have a personality, or friendliness.


The unexpanded Vic-20 requesting the user to press play on the data cassette, to load a program.

My real introduction to using personal computers however, happened during my Art Teaching degree in 1988, using on-campus Amiga 500 computers for producing two-dimensional graphics in a paint program, and IBM Clones (probably of the 286 variety) for word processing on screens that allowed displays of chunky text characters in about 8 different colours. My father saw that I was getting interested in computing, and he sent me his faithful but no longer required Vic-20 computer to see if I could find it useful. I found it very useful to have my own computer, even though it didn't have the graphics power of the Amiga 500, or the processing power of the PC clones. I taught myself how to program in BASIC, and in machine code (for processing speed). I was soon using the Vic-20 for word processing for my course. I now didn't have to rely on booking times in the computer labs to do my word processing. And I was using the Vic-20 to do more and more graphics tasks (my main interest in using computers).

The Vic-20 computer was an 8-bit computer which used a 6502 microprocessor and a 6561 Video Interface Chip (display chip), giving the computer its name. The unexpanded computer came with about 3.5 Kilobytes of RAM for programming (miniscule by today's computers' standards) and it had a possible ‘high resolution’ graphics display of 176 pixels wide, by 184 pixels high. The computer didn't come with any special graphics routines for drawing lines or circles, so I needed to research how to produce such things. I remember being surprised and disappointed by how complex the task of drawing a line on the screen was. One of the first things I did was to expand my Vic-20 with some extra RAM. This provided more space for programming, especially for programs involving custom graphics.

On the first page of this month's display, I present some images from the Vic-20 computer running various commercial software, to give an idea of the computer's general graphics capabilities. The images used in this month's display were taken as screen captures from using WinVICE 2.1 (an excellent Vic-20 emulator, that runs on Windows computers).


Continue with the first page