This sets the background to yellow, and then clears the whole graphics screen

to that colour. All GCOL numbers greater than 127 change the background

colour.

RUN the program again after editing line 10 to be:

10 MODE 130

Mode 130 is a low-resolution mode giving much thicker lines, but up to eight

colours can be displayed simultaneously, along with eight pairs of flashing

colours.

Note that GCOL 0,2 gives green and not yellow in this mode. The numeric

references to colour are not the same in all the graphics modes. You must refer

to Appendix 1 for the correct GCOL number to produce a particular colour.

In mode 130, GCOL 0 can be followed by any number from 0 to 15 to select a

colour. Try changing the GCOL statements to see its effects.

The PLOT command

The PLOT command is an all-purpose drawing command. MOVE and DRAW

are special examples of PLOT. Because moving and drawing are used so

frequently, the PLOT commands that produce these effects have been given

equivalent keywords:

PLOT 4,100,100 is the same as MOVE 100,100

PLOT 5,800,100 is the same as DRAW 800,100

The first number after PLOT decides how the lines are plotted. PLOT

commands enable rectangles, parallelograms, circles, segments, sectors, arcs,

triangles or ellipses to be drawn in outline, solid colour or patterned. You have

seen this demonstrated in the Welcome software. A program to draw a solid

rectangle is:

10 MODE 129

15 REM move to one corner of rectangle

20 MOVE 100, 100

25 REM move to diagonally opposite corner

30 PLOT 101,800,900

C 16