Earlier you saw that after running a program you can clear the screen by

typing:

CLS RETURN

You can also clear the screen with:

CLG RETURN

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 RETURN

RUN RETURN

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 RETURN

GCOL 0,130 RETURN

CLG RETURN

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