Nascom News­let­ter

Low resolution graphics – 391 by 256 points with one of eight colours per pixel.

High resolution graphics display giving a resolution of 784 by 256 with one of two colours per pixel (on/off monochrome)

Mixed density graphics display giving resolutions of 391 by 256 and 784 by 254 combined, with each pixel having one of four colours.

Mixed text and graphics – the Nascom 2 video RAM output combined with one of the graphics displays.

COLOUR

This command specifies the colour to be used in succeeding commands. In addition to just specifying a single colour (one of the eight already mentioned) the AVC allows the use of special shading colours which can be used to differentiate areas such as graphs or shadows in pictures. These shading colours are specified to the computer as the relative levels of the three primary components of colour (red, green and blue), allowing a selection of 4913 different colours.

BACKGND

This allows the whole of the display to be set to a specified colour in a background colour. Again up to 4913 colours are available.

DEFAULT

This is a special command that sets up all the default values of the command parameters.

ORIGIN

This command is used to specify the centre of rotation to be used in those commands which allow a rotation to be specified.

PEN

This command has two functions – to select the combination of primary colours which are available for drawing purposes (as distinct from MODE, which determines which colours will be displayed after shapes are drawn) and to specify how the shapes are to drawn. This last parameter is rather difficult to explain – shapes can be drawn as they would be with coloured pens on paper, but they can also be draw in other ways. These other ways produce effects which change the shapes appearance and colour. The effects are similar to television visual effects.

WINDOW

This command instructs the computer which parts of the display can be used for the output of graphics or text. It can be used to protect areas of the screen so that they cannot be over-written.

DUMP

This command allows the picture which would normally be displayed on the screen to be output to a matrix printer with dot graphics capability.

GSAVE

This allows the user to save the current display picture on disc.