Sinclair QL Beginner's Manual page 49

are different and the LET helps to emphasise this. However if there are two or a few LET statements
doing some simple job such as setting initial values, an exception may be made.
For example:
100 LET first = 0
110 LET second = 0
120 LET third = 0
may be re-written as
100 LET first = 0 : second = 0 : third = 0
without loss of clarity or style. It is also consistent with the general concept of allowing short forms of
other constructions where they are used in simple ways.
The colon : is a valid statement terminator and may be used with other statements besides LET.
THE BASIC SCREEN
In a later chapter we will explain how other graphics facilities, such as drawing circles, can be handled
but here we outline the pixel-oriented features. There are two modes which may be activated by any
of the following:
Low resolution
8 Colour Mode
256 pixels across, 256 down
High resolution
4 Colour Mode
512 pixels across, 256 down
In both modes pixels are addressed by the range of numbers:
0 - 511 across
and 0 - 255 down
Since mode 8 has only half the number of pixels across the screen as mode 4, mode 8 pixels are
twice as wide as mode 4 pixels and so in mode 8 each pixel can be specified by two coordinates. For
example:
0 or 1 2 or 3 510 or 511
It also means that you use the same range of numbers for addressing pixels irrespective of the mode.
Always think 0-511 across and 0-255 down.
If you are using a television then not all the pixels may be visible.
The colours available are:
MODE 256
Black
Blue
Red
Magenta
Green
Cyan
MODE 256
MODE 8
MODE 512
MODE 4
Code MODE 512
0 Black
1
2 Red
3
4 Green
5