Backround

 BBS: Inland Empire Archive
Date: 04-19-92 (00:12)             Number: 189
From: DANIEL CORBIER               Refer#: NONE
  To: MIKE MELAMED                  Recvd: NO  
Subj: Backround                      Conf: (2) Quik_Bas

MM>How do you get background of a certain spot 1,1 for
MM>example? I know that to get forground, you should do this:
MM>A=SCREEN(1,1,1):A=A AND 15

A AND 15 will not yield correct results for forground colors > 15.

Use the following:

Attribute  = SCREEN(1,1,1)
-----------------------------------------------------------
Forground  = (Attribute AND 15) + (Attribute AND 128) \ 8
Background = (Attribute AND 112) \ 16
-----------------------------------------------------------

The  '\'  instead of  '/' is for integer division.

Let me try to elucidate what is going on.
The color attribute is stored in an 8-bit pattern as follows:
(each X is 0 or 1)

7        6        5        4        3        2        1        0
X        X        X        X        X        X        X        X
_        ___________________        _        ___________________
|                 |                 |                 |
Blinking          |             Intensity             |
                  |                                   |
                  |                                   |
             Background                           Forground


With that in mind, to get the BACKGROUND we do:

        X X X X X X X X                 'Attribute
AND     0 1 1 1 0 0 0 0                 'background mask (binary for 112)
-------------------------
        0 X X X 0 0 0 0
Div by  2^4                             'Moves result over 4 columns
=========================
        0 0 0 0 0 X X X                        'Background color


For the FORGROUND:

        X X X X X X X X                 'Attribute
AND     0 0 0 0 1 1 1 1                 'Forground & intensity mask (15)
-------------------------
        0 0 0 0 X X X X                 'Part one

Add to that:
        X X X X X X X X                 'Attribute
AND     1 0 0 0 0 0 0 0                 'blinking mask (&b10000000 = 128)
-------------------------
        X 0 0 0 0 0 0 0
Div by  2^3                             'Move it over 3 columns
-------------------------
        0 0 0 X 0 0 0 0                 'Part two

Which gives us the final forground operation:

        0 0 0 0 X X X X                 'Part one
Add        0 0 0 X 0 0 0 0                 'Part two
========================
        0 0 0 X X X X X                 'Forground color


--- Maximus 2.00
 * Origin: Telcom Central (1:135/23)