PALETTE Statement Details

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◄QuickSCREEN► ◄Details► ◄Example► ◄Contents► ◄Index► ────────────────────────────────────────────────────────────────────────────── 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.