The first 5 images shown on this page were produced on a 160 x 176 pixel Vic-20 high-resolution bitmap screen (the maximum that the Vic-20 could display in high-resolution graphics). The remaining images were produced on my larger 320 x 352 pixel bitmap screen that was held in memory, and partly displayed on the Vic-20 computer as a 160 x 176 pixel 'window' view into that whole bitmap screen. Some use the whole 320 x 352 pixel screen, while others just use the 160 x 176 pixel 'window' image.

Most of these images make use of 'exclusive-or plotting', where as each pixel is plotted, if the pixel was already black, the program would change it to be a white pixel, or if the pixel was already white, the program would change change it to be a black pixel. For example, on the first image (below), where two black rectangles overlap becomes a white rectangle.

160 x 176 pixels, produced on a Vic-20 computer.

A small series of rectangles applied with the 'exclusive-or' mode. Any overlapping of the shapes results in a negative shape.

160 x 176 pixels, produced on a Vic-20 computer.

A small series of rectangular lines and filled shapes applied with the 'exclusive-or' mode. Any overlapping of the shapes or lines results in negative shapes or lines being created respectively.

160 x 176 pixels, produced on a Vic-20 computer.

160 x 176 pixels, produced on a Vic-20 computer.

Lots of reversing tones from intersecting shapes and lines, and some rectangles of 'pattern tone'.

160 x 176 pixels, produced on a Vic-20 computer.

Lots of reversing tones from intersecting shapes and lines.

320 x 352 pixels, produced on a Vic-20 computer.

Lots of reversing tones from intersecting shapes and lines, and some rectangles of 'pattern tone'.

320 x 352 pixels, produced on a Vic-20 computer.

The machine code routine used for producing circles on my 320 x 352 large bitmap image is based on Bresenham's Circle Algorithm. The aspect ratio can be modified to produce ovals. With the way that the lines jump from one pixel row or column to the next, this image contains a number of interesting patterns as part of the way the circles are produced.

160 x 176 pixels, produced on a Vic-20 computer.

160 x 176 pixels, produced on a Vic-20 computer.

160 x 176 pixels, produced on a Vic-20 computer.

This design, to me, feels like it represents a motorbike.

320 x 352 pixels, produced on a Vic-20 computer.

Produced using the included machine code routines. Note the use of 'image clipping'. Most graphic operations such as drawing lines or drawing circles, could be drawn from points that might lay outside the realm of the bitmap screen. Any such points were still calculated but not drawn, so that the effects of any such use of lines or circles was still accurate.

320 x 352 pixels, produced on a Vic-20 computer.

This interesting figure is the result of starting with plotting a pixel between 3 points of a triangle, then repeating the process of randomly choosing one of the triangle points and plotting a pixel halfway towards that chosen triangle point. I set up my program to continue the above repeated process until I pressed the space bar. This idea came from the Polish mathematician Waclaw Sierpinski, as described in the book, "Chaos" by James Gleick (published by Cardinal, Sphere Books, London, UK, 1988).

320 x 352 pixels, produced on a Vic-20 computer.

This image is based on a grid of straight-lined spirals. A few of the spirals were reversed, and one spiral is positioned off-centre to make it feel a little 'out of place'.

The image was constructed using my program's ability to copy and paste rectangular sections of the image, as well as move about the image using a configurable grid.