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PALETTE, PALETTE USING Statements Details
◄Syntax► ◄Details► ◄Example► ◄Contents► ◄Index► ◄Back►
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The PALETTE statement changes one or more colors in the palette. The
PALETTE statement works only on systems equipped with the EGA, VGA, or
MCGA adapters. The PALETTE statement is not supported in screen mode 3 or 4.
PALETTE [attribute%,color&]
■ The argument 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 can be used with the IBM Enhanced Graphics Adapter (EGA).
■ The table below lists attribute and color ranges for various adapter
types and screen modes. See the SCREEN statement for a list of
colors available for various screen modes, monitor, and graphics
adapter combinations.
Attri-
SCREEN Monitor bute Color PALETTE
mode attached Adapter range range supported
══════ ══════════════════ ═══════ ═════ ════════════ ═════════
0 Monochrome MDPA 0-15 No
Monochrome EGA 0-15 0-2 Yes
Color CGA 0-15 No
Color/Enhanced(1) EGA 0-15 0-15/0-63 Yes
Analog VGA 0-15 0-63 Yes
Color/Analog MCGA 0-15 0-63 No
1 Color CGA 0-3 0-15(2) No
Color/Enhanced(1) EGA 0-3 0-15 Yes
Analog VGA 0-3 0-15 Yes
Color/Analog MCGA 0-3 0-15 No
2 Color CGA 0-1 No
Color/Enhanced(1) EGA 0-1 0-15 Yes
Analog VGA 0-1 0-15 Yes
Color/Analog MCGA 0-1 0-15 No
3 Monochrome HGC 0-1 No
4 Color/Enhanced OCGA/(7) 0-1 0-15(3) No
OEGA/(7)
OVGA(7)
7 Color/Enhanced(1) EGA 0-15 0-15 Yes
VGA 0-15 0-15 Yes
8 Color/Enhanced(1) EGA 0-15 0-15 Yes
VGA 0-15 0-15 Yes
9 Enhanced(1) EGA(4) 0-3 0-63 Yes
Enhanced(1) EGA(5) 0-15 0-63 Yes
Analog VGA 0-16 0-63 Yes
10 Monochrome EGA 0-3 0-8 Yes
Analog VGA 0-3 0-8 Yes
11 Analog VGA 0-1 0-262,143(6) Yes
Analog MCGA 0-1 0-262,143(6) Yes
12 Analog VGA 0-15 0-262,143(6) Yes
13 Analog VGA 0-255 0-262,143(6) Yes
Analog MCGA 0-255 0-262,143(6) Yes
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(1) IBM Enhanced Color Display.
(2) Color range available for attribute 0 only.
(3) Color range available for attribute 1 only.
(4) With 64K of EGA memory.
(5) With more than 64K of EGA memory.
(6) Range of display colors is actually from 0 to 4,144,959, but
only 262,144 of these can be displayed.
(7) Olivetti CGA, EGA and VGA
PALETTE USING array-name [(array-index)]
■ The argument array-name is an array that contains more than one display
color. It must be a long integer array for VGA and MCGA adapters in
screen modes 11 to 13. Otherwise, the array can be either an integer
or long-integer array.
■ The argument array-index is the index of the first array element
to use in setting the palette.
■ With USING PALETTE, all entries in the palette can be modified in
one statement. Each attribute in the palette is assigned a
corresponding color from the array.
- A color argument of -1 in the array leaves the attribut
unchanged in the palette. (All other negative numbers are
invalid values for color.)
- The dimensions for the array must be large enough to set all
the palette entries after array-index. For example, if you
are assigning colors to a palette with 16 attributes and the
argument array-index is 5 (the first array element to use
in resetting the palette), then the dimensions for the array
must be large enough to hold at least 20 elements (because
the number of elements from 5 to 20, inclusive, is 16):
DIM PAL%(20)
' Other statements can go here.
PALETTE USING PAL%(5)
Usage Notes
■ The PALETTE statement provides a way of mapping display colors
(the actual binary values used by the adapter) to color attributes
(a smaller set of values).
■ When a program enters a screen mode, the attributes are set to a
series of default color values. See the ◄SCREEN Statement Details►
for a list of the default colors.
║ Note: In the EGA, VGA, and MCGA adapters the default values
║ have been selected so the display shows the same colors,
║ even though the EGA uses different color values.
Use the PALETTE statement to assign different colors to the attributes.
■ Use a PALETTE statement with no arguments to set the palette back to
the default color values.
■ After a PALETTE statement is executed with arguments, the graphics
adapter subsequently uses the display color associated with the
attribute whenever an attribute argument appears in a statement
such as DRAW or LINE. Changing the display color assigned to an
attribute changes those colors currently displayed on the screen
associated with that attribute. 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 following DRAW statement selects
attribute 3, and draws a line of 100 pixels using the display
color associated with attribute 3, in this case also 3:
DRAW "C3L100"
If the following statement is executed, the color associated with
attribute 3 is changed to color 2:
PALETTE 3,2
All text or graphics currently on the screen displayed using
attribute 3, including the line that is 100 pixels long, 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.
■ Attribute 0 is always the screen background color. 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.
■ You also can use the COLOR statement to change the screen background
color in modes 1 and 7 through 10.
■ The 64 EGA colors are derived from four levels each of red, green,
and blue. For example, black is composed of red, green, and blue
levels of (0,0,0), bright white is (3,3,3), dark gray is (1,1,1), etc.
The best way to see the BASIC color code (0 through 63) associated with
each combination of red, green, and blue levels is to run the
following program:
' Display the EGA color codes 1 through 63
' using color code 0 (black) as background.
DEFINT A-Z
SCREEN 9 ' Establish EGA screen mode.
' Display a set of nine color bars.
FOR CC% = 1 TO 9
LINE (((CC% * 64) - 24), 40)-STEP(60, 140), CC%, BF
NEXT CC%
' Display seven sets of nine color bars.
' A new set is displayed each time user presses a key.
FOR Set% = 0 TO 6
FOR ColorBar% = 1 TO 9
DisplayCode% = (Set% * 9) + ColorBar%
LOCATE 15, (ColorBar% * 8)
PRINT DisplayCode%
PALETTE ColorBar%, DisplayCode%
NEXT ColorBar%
SLEEP
NEXT Set
END
■ To calculate a VGA 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
This formula yields integer values from 0 to 4,144,959, but
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 intensity value calculation would be
gray value = (.11 * 45) + (.59 * 20) + (.30 * 20) = 22
The fractional part of the result is dropped.