Topic       : The GFA-Basic Compendium
Author      : GFA Systemtechnik GmbH
Version     : GFABasic.HYP v2.98 (12/31/2023)
Subject     : Documentation/Programming
Nodes       : 899
Index Size  : 28056
HCP-Version : 3
Compiled on : Atari
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@hostname   : CAB     
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View Ref-FileCOLOR color
SETCOLOR register,red,green,blue
SETCOLOR register,composite
VSETCOLOR color,red,green,blue
VSETCOLOR color,composite

register, red, green, blue, composite, color: iexp

The command COLOR determines the line color. Values between 0 and 255,
dependant on the current resolution, are valid.

The first variant of SETCOLOR determines the proportion of the colors red,
green, and blue in a particular color register. The intensity of the color
element is specified on a scale from 0 (low) to 15 (high) and the number of
available color registers depends on the current resolution. In the second
variant of SETCOLOR, the color setting is defined by a single parameter whose
value is computed by the following formula:

    composite = red * 256 + green * 16 + blue * 1

and, as with the other setting, the values for red, green, and blue are
specified on a scale from 0 to 15.

The setting of color elements in the color registers is, naturally, only
applicable when in the color modes. However, in the monochrome mode, when a
composite value other than 0 or 1 is specified, even numbers have the same
effect as 0 and odd numbers the same effect as 1.

Example:

    SETCOLOR 0,0

--> On a mono monitor, the display appears as white on a black background.

Through an apparently unexpected mix-up in the design of the operating system,
the color registers used by SETCOLOR do not correspond directly to the numbers
used by COLOR. To overcome this the command VSETCOLOR is available.

The values of red, green, and blue are numbers in the range 0 to 15. The term
composite is calculated in the same manner as SETCOLOR, i.e.:

    composite = red * 256 + green * 16 + blue * 1

VSETCOLOR 1,2,3,4 is the same as VSETCOLOR 1,&H234

The syntax of the VSETCOLOR command is virtually identical to that of SETCOLOR,
the sole difference being in the parameters 'register' and 'color'. They are
related as shown:

For monochrome modes:
SETCOLOR 0,even   corresponds to   VSETCOLOR 0,0
SETCOLOR 0,odd    corresponds to   VSETCOLOR 0,&HFFF

For 4 color modes:
SETCOLOR   00  01  02  03
VSETCOLOR  00  02  03  01

For 16 color modes:
SETCOLOR   00  01  02  03  04  05  06  07  08  09  10  11  12  13  14  15
VSETCOLOR  00  02  03  06  04  07  05  08  09  10  11  14  12  15  13  01

For 256 color modes:
See 256 color VDI/Hardware table.

Example:

    ' In Low resolution
    FOR i%=0 TO 15
      DEFFILL i%
      PBOX i%+20,0,319,199
    NEXT i%
    DO
      a%=INP(2)
      EXIT IF a%=27
      VSETCOLOR a% AND 15,RAND(-1)
    LOOP

--> This program draws overlapping color boxes, the result being 16 vertical
    bars (the left hand one is the same color as the border, i.e.  color 0). By
    ANDing the key code with 15, a color register number can be chosen and this
    register is then set to a random value. The program is left by using the
    Escape key.

Memo: 'VSETCOLOR i,rgb' contains a bug such that the red and blue values
      end up swapped. This happens in the editor and compiled.

      SETCOLOR uses a 15-bit mask that should be 12-bits (editor bug only).
        'rrrrggggbbbb'

      When using vq_color() always set 'flag' to 1, otherwise you can get
      values greater than 1000.

vsl_color()+, vs_color()+, EsetColor()+, Setcolor()+, vq_color()+