46 background – but not the colour of any graphics: for that you need to use another BASIC keyword – GCOL , which stands for Graphics COLour. Graphics Now for the graphics: when drawing lines and triangles positions on the screen are given with two numbers (the X and Y coordinates). The point A has coordinates 600 across, 0 up. The point B is at position 100,500 and C is at 800,800. The statement DRAW 800,800 will draw a line from the last point ‘visited’ to 600,600. If no point has been visited, the computer will assume that it starts from the point 0,0. To move without drawing a line use the command MOVE .
So to draw a line from 1000,0 to 1000,600 type MOVE 1000,0 RETURN DRAW 1000,600 RETURN DRAW 100,500 will draw another line, and so on. As well as MOVE and DRAW there are PLOT commands for other effects. These are described in a later chapter. The statement GCOL is used to change the graphics colour used by the DRAW statement. GCOL is followed by two numbers, the first is normally zero and the second determines the graphics colours, eg: GCOL 0,0 Black lines GCOL 0,1 Red lines GCOL 0,2 Yellow lines GCOL 0,3 White lines