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PALETTE Statement Details
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PALETTE Statement Details
Syntax
PALETTE [attribute,color]
PALETTE USING array-name [(array-index)]
Argument Description
attribute The palette attribute to be changed.
color The display color number to be assigned to the
attribute. The color must be a long integer expression
for the IBM Video Graphics Array adapter (VGA) and IBM
Multicolor Graphics Array adapter (MCGA) in screen
modes 11 to 13. Integer or long-integer expressions
may be used with the IBM Enhanced Graphics Adapter
(EGA).
array-name An array containing the color numbers to be assigned
to the attributes available in the current screen
mode. The VGA and MCGA adapters require a long integer
array in screen modes 11 to 13. With the EGA this can
be either an integer or long-integer array.
array-index The index of the first array element to use in setting
the palette.
The PALETTE statement works only on systems equipped with the EGA,
VGA, or MCGA adapters.
The statement provides a way of mapping display colors (the actual
binary values used by the adapter) to color attributes (a smaller
set of values). All BASIC graphics statements such as CIRCLE, COLOR,
DRAW, or LINE use color attributes rather than display-color values.
When a program enters a screen mode, the attributes are set to a series
of default color values. (See the SCREEN statement for a list of the
default colors.) In the EGA, VGA, and MCGA adapters these default
values have been selected so the display shows the same colors, even
though the EGA uses different color values.
With the palette statement you can assign different colors to the
attributes, giving you greater control over the colors on the display.
A PALETTE statement with no arguments sets the palette back to the
default color values.
When you execute a PALETTE statement with arguments, the adapter
subsequently uses the display color (indicated by color) whenever
the value attribute appears in a statement like DRAW or LINE that
specifies a color. Changing the display color assigned to an attribute
changes the color on the screen immediately.
For example, assume that the current palette contains colors 0, 1,
2, and 3 in the four attributes numbered 0, 1, 2, and 3. The DRAW
statement
DRAW "C3L100"
selects attribute 3, and draws a line of 100 pixels using the display
color associated with attribute 3, in this case also 3. If the
statement
PALETTE 3,2
is executed, then the color associated with attribute 3 is changed
to color 2. All text or graphics currently on the screen displayed
using attribute 3 are instantaneously changed to color 2. Text or
graphics subsequently displayed with attribute 3 are also displayed
in color 2. The new palette of colors contains 0, 1, 2, and 2.
With the USING option, all entries in the palette can be modified
in one PALETTE statement. The array-name argument is
the name of an integer or long-integer array and the array-index
specifies the index of the first array element in the array-name
to use in setting the palette. Each attribute in the palette
is assigned a corresponding color from this array. The array must
be dimensioned large enough to set all the palette entries after
array-index. For example, if you are assigning colors to all 16
attributes, and the index of the first array element that is given
in your PALETTE USING statement is 5, then the array must be
dimensioned to hold at least 20 elements (since the number of
elements from 5-20, inclusive, is 16):
DIM PAL%(20)
.
.
.
PALETTE USING PAL%(5)
A color argument of -1 in the array leaves the attribute
unchanged. All other negative numbers are invalid values for color.
You can use the COLOR statement to set the default foreground
color and the background display color. The foreground color argument
specifies the way text characters appear on the display screen. Under
a common initial palette setting, points colored with the attribute
0 appear black on the display screen. Using the PALETTE statement,
you could, for example, change the mapping of attribute 0 from black
to white.
The table below lists attribute and color ranges for various adapter
types and screen modes.
The VGA uses a different way of calculating color values from the
EGA. To calculate a color value, select the intensities of red, green,
and blue. The intensity of a color is a number from 0 (low intensity)
to 63 (high intensity). Then use the following formula to calculate
the actual color number:
color number = 65536 * blue + 256 * green + red
Because there are gaps in the range of color numbers, you should use
the formula rather than just select a number.
When used with the IBM Analog Monochrome Monitor, the VGA color values
are converted to a gray-scale value by taking a weighted sum of the
red, blue, and green intensities:
gray value = 11% blue + 59% green + 30% red
For example if the blue, green, and red intensities are 45, 20, and
20, the gray value would be .11*45+.59*20+.30*20 or 22 (the fraction
in the result is dropped).
See the SCREEN statement for the list of colors available for
various screen-mode, monitor, and graphics-adapter combinations.
Screen Color and Attribute Ranges
SCREEN Monitor Adapter Attribute Color
Mode Attached Range Range
0 Monochrome MDPA 0-15 N/A
Monochrome EGA 0-15 0-2
Color CGA 0-15 N/A
Color/Enhanced(b) EGA 0-15 0-63
N/A VGA 0-15 0-63
N/A MCGA 0-15 N/A
1 Color CGA 0-3 N/A
Color/Enhanced(b) EGA 0-3 0-15
N/A VGA 0-3 0-15
N/A MCGA 0-3 N/A
2 Color CGA 0-1 N/A
Color/Enhanced(b) EGA 0-1 0-15
N/A VGA 0-1 0-15
N/A MCGA 0-1 N/A
7 Color/Enhanced(b) EGA 0-15 0-15
N/A VGA 0-15 0-15
8 Color/Enhanced(b) EGA 0-15 0-15
N/A VGA 0-15 0-15
9 Enhanced(b) EGA(c) 0-3 0-63
Enhanced(b) EGA(d) 0-15 0-63
N/A VGA 0-16 0-63
10 Monochrome EGA 0-3 0-8
N/A VGA 0-3 0-8
11 N/A VGA 0-1 0-262,143(e)
N/A MCGA 0-1 0-262,143(e)
12 N/A VGA 0-15 0-262,143(e)
13 N/A VGA 0-255 0-262,143(e)
N/A MCGA 0-255 0-262,143(e)
____________________________________________________________________
N/A = Not Applicable
(b) With 64K of EGA memory
(c) With more than 64K of EGA memory
(d) IBM Enhanced Color Display
(e) Display colors are not numbered from 0 to 262,143. See above.
Note: Because of their wide range of colors, the VGA and MCGA adapters
require a long-integer array in the PALETTE USING statement
in screen modes 11 to 13.