Chapter
8
I
Displaying
Color
and
Graphics
The aspect ratio is important when drawing objects on the
screen. Keep in mind that the number
of
horizontal points per
inch is greater than the same number
of
vertical points per inch.
Therefore,
for
example, if you try
to
draw a square, the perime-
ter
of
the square must contain more horizontal points than verti-
cal
points.
Also, because there is
a
difference in points per inch among the
different screen modes, images that specify the same coordinates
do not look the same in different modes.
Colors
Colors are selected by numbers that vary, depending on whether
you are in
a
screen mode that supports
2,
4,
or 16 color sets. All
modes start with the background as black and the foreground as
white. Each color set has a defined list
of
colors called a palette.
The characteristics
of
each mode are:
2
Color
Set
is the black and white mode; the background is
black and the foreground is white. You cannot change these
colors.
4
Color
Set
has
1
palette
of
4
colors available at all times in
Screen Modes
4
and
6.
The colors are numbered
0-3.
Color
0
is
the current background color. The other colors are:
Number Color
1
2
3
cyan
magenta
white
BASIC uses Color
3
as the foreground color if you do not specify
a color parameter with graphic statements. Background can be
any one
of
the 16 colors described in the 16 Color Set. See the
PALETTE statement for information on changing colors in the
palette.
78
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