Appendix 8

PLOT codes

The BASIC PLOT statement can be summarised as:

PLOT code,x,y

and its effect is to plot to the point (x,y) in a manner determined by the value of

code. An identical effect can be produced using:

VDU 25,code,x;y; (note the use of semicolons).

The permissible PLOT codes and their effects are given (in groups of eight

codes) in Table 1. The codes within each group are obtained by adding an 'offset'

value to the first code in the group. The offset values are as follows:

0 move relative to the previous point;

1 plot relative to the previous point in the current graphics

foreground colour;

2 plot relative to the previous point in the logical inverse colour;

3 plot relative to the previous point in the current graphics

background colour;

4 move to absolute position;

5 plot to absolute position in the current graphics foreground colour

6 plot to absolute position in the logical inverse colour;

7 plot to absolute position in the current graphics background

colour.

The column headed Previous points contains the number of points which must

have been 'visited' before the corresponding PLOT statement is executed. For

example, in order to plot a rectangle, one corner must be first be visited

(perhaps using MOVE or DRAW) -- the co-ordinates of the diametrically

opposite corner are specified in the PLOT statement.

Examples of various PLOT commands are given in Chapter C, and detailed

information can be found in the Reference Manual.

App 8.1