137 29 Advanced graphics As we saw earlier, the following keywords can be used in a variety of statements which produce high resolution graphics effects on the screen: GCOL Selects the colour and drawing ‘style’ of any graphics (except in MODES 3 , 6 , or 7 ) MODE Selects a particular graphics MODE DRAW Draws lines (except in MODES 3 , 6, or 7 ) MOVE Moves the graphics cursor (except in MODES 3 , 6 , or 7 ) PLOT Draws lines, dotted lines, points and colours in triangles (except in MODES 3 , 6 , or 7 ) These will only become familiar with use. What follows is a description of how to use some of the keywords to produce a selection of results on the screen.
How to change the screen display modes The screen mode can be changed at any time by typing MODE X, where X is the value 0 to 7 from the following list:
MODE 0 Uses two colours with very high resolution and requires 16K of memory to ‘map’ the screen MODE 1 Uses four colours with high resolution and requires 16K of memory MODE 2 Uses four colours with medium resolution graphics – 16K MODE 3 Text only – 16K MODE 4 Two colours and high resolution graphics – 8K MODE 5 Four colours and medium resolution graphics – 8K MODE 6 Text only – 8K MODE 7 Teletext (which is the subject of a separate chapter of this book)– 8K In MODES 0 , 1 , 2 , 4 and 5 the screen is divided up into imaginary rectangles, like a piece of graph paper.
In MODE 0 there are 640x256 squares; in MODE s 1 and 4 there are 320x256 and in MODE s 2 and 5 there are 160x256 (in other words, the higher the resolution of the graphics, the smaller the rectangle). The higher the resolution , the more memory is used up in the process of ‘mapping’ the screen.