Earlier you saw that after running a program you can clear the screen by
typing:
CLS
You can also clear the screen with:
CLG
Although both commands appear to have the same effect, CLS actually clears
the text screen and CLG clears the graphics screen. Normally these are exactly
the same and fill the whole screen. Later you will see that the areas in which
text and graphics appear can be separated, and so it is useful to have two
commands for clearing the screen.
The lines drawn in mode 128 are the finest that your computer can produce,
and so this mode is used whenever very accurate high-resolution graphics are
needed. The same program runs in other graphics modes, as you can see if you
edit line 10 and then run the program again, i.e. type:
10 MODE 129
RUN
This time the lines produced are thicker -- mode 129 is a medium-resolution
mode. The main advantage it offers over mode 128 is that it allows the display
of four colours at the same time. You can change the colour of the lines by
adding:
35 GCOL 0,1
45 GCOL 0,2
and running the program again. GCOL is used to select the colour to be used in
the DRAW statement. The number following GCOL 0, is related to a particular
colour in each mode. In mode 129:
GCOL 0,0 gives black lines
GCOL 0,1 gives red lines
GCOL 0,2 gives yellow lines
GCOL 0,3 gives white lines
Once a colour has been selected, it is automatically used in all further DRAW
statements until a new GCOL command is given.
GCOL can also be used to change the background graphics colour. For
example, type:
MODE 129
GCOL 0,130
CLG
15
C 15