Palette changes via Interrupt: Incompatible color numbers

[Hans Ruegg]

In SCREEN 12, I tried to modify the RGB values of the displayed colors
using Interrupt &H10, as such modifications seem not to be possible
with the PALETTE statement. But I discovered that the color numbers
used by the Interrupt services were not identical with the color numbers
used by PowerBasic. To verify this, I wrote a small test program which
is reproduced below. I found that color numbers 0 to 5 and 7 were
identical, but in order to change the color no.6, I had to input 20
(decimal), and for changing colors 8 to 15, I had to input numbers
from 56 to 63.
This anomaly occurred only when setting the screen mode with the SCREEN
statement, but not in a similar program which sets the screen mode via
Interrupt &H10, (In that case, of course, the graphics statements like
LINE, PAINT, etc. are not available.) Neither did it occur in QuickBasic,
only in PowerBasic.
Now my question: Is this anomaly inherent to PowerBasic, so that it
will produce the same results on all VGA systems, or might it depend on
the BIOS type, the video card, or some other factor beyond my control?
I would like to implement palette changes in a program, but I need to
be sure it will not produce unexpected results on different systems.

Hans Ruegg

'=========== TEST PROGRAM "BLINK" ================
'Lets the user input a color index and lets the corresponding
'color blink for half a second.
'Input of a negative index will terminate the program.

SCREEN 12
GOSUB displayColors
DO
GOSUB changeColor
LOOP UNTIL indx%<0
SCREEN 0
END

displayColors: 'display squares in all 16 colors
FOR row%=0 TO 3: FOR colu%=0 TO 3
cl% = 4*row%+colu%
LINE (48*colu%, 48*row%)-(48*colu%+45, 48*row%+45), cl%, BF
LOCATE 3*row%+2, 6*colu%+3: PRINT TRIM$(STR$(cl%));
NEXT colu%: NEXT row%
RETURN

changeColor:
LOCATE 25,1: PRINT "No. to change: "
LOCATE 25,15: INPUT indx%
IF indx%<0 THEN RETURN
blink indx%
RETURN

'=============================================================

SUB blink (ind%)
'Lets the color no. ind% blink for half a second in its opposite color

getDAC ind%, red%, green%, blue%
putDAC ind%, red% XOR 63, green% XOR 63, blue% XOR 63
t!=TIMER
DO: LOOP UNTIL TIMER>t!+0.5
putDAC ind%, red%, green%, blue%
END SUB

SUB putDAC (ind%, red%, green%, blue%)
'Sets new RGB values in the VGA palette for color no. ind%

REG 1, &H1010
REG 2, ind%
REG 3, 256*green% + blue%
REG 4, 256*red%
CALL INTERRUPT &H10
END SUB

SUB getDAC (ind%, red%, green%, blue%)
'Retrieves the RGB values of the current VGA palette for color no. ind%

REG 1, &H1015
REG 2, ind%
CALL INTERRUPT &H10
gb% = REG(3)
green% = gb%\256: blue% = gb% AND 255
red% = REG(4)\256
END SUB

'============================================================

[Alan Earnshaw]

Hans,

We covered this topic in some detail a few years ago in BASICally Speaking. You might wish to take a look at our back issue list ( http://www.infoms.com/backiss.htm ) and download some source code from the online archives ( http://www.infoms.com/archives.htm ). Back issues cost $4.00 each, but you cam download the code for free.

Alan

------------------
Alan C. Earnshaw
Information Management Systems, Inc.
http://www.infoms.com

[Hans Ruegg]

Hans Ruegg.


Thank you, Alan, for your hints! I found the corresponding source code
which covered the gap in my knowledge: Interrupt 10h, function 1007h
to retrieve the DAC register numbers associated with the palette
indices. Besides, I found that there is also a function 1000h which
allows to associate the register numbers with new palette indices.
So I prefer to set all 15 color indices to their corresponding register
numbers during my program. (Example code below, using part of your
source code.) This works in SCREEN 12, and I suppose it should work
also in a DOS mode text screen.
However, it does NOT work in a DOS Text window under Windows (neither
does the Fade routine on your site). It seems that Windows has a
different way of definig the colors in a DOS box. Maybe somebody has
investigated this point?

Hans Ruegg.

'=================================================================
'Code to set DAC Register Numbers to corresponding Palette indices
'=================================================================
DIM Regis?(0 TO 15)
DIM Settings?(0 TO 15, 0 TO 2)

SCREEN 12

FOR c? = 0 TO 15
  Regis?(c?) = WhichRegister?(c?)
  getDAC Regis?(c?), Settings?(c?,0), Settings?(c?,1), Settings?(c?,2)
  SetRegister c?, c?
NEXT c?

'===============================================================
'Modify here the palette settings as you like.
'Register numbers 0 to 15 correspond now to color indices 0 to 15.
'Following code is an example.

CLS
FOR c? = 0 TO 15
  COLOR c?
  PRINT "COLOR "; c?
  LINE (320,16*c?)-(400,16*c?+14),c?,BF
NEXT c?
PRINT "Press any key to modify palette:"
DO: LOOP WHILE INKEY$=""

'Set a palette shifting gradually from blue to orange:
FOR c? = 0 TO 15   
  putDAC c?, 4*c?, 16+c?, 63-4*c?
NEXT c?

PRINT "Press any key to restore palette:"
DO: LOOP WHILE INKEY$=""

'==============================================================
' Restore original settings
'==============================================================
FOR c? = 0 TO 15
  SetRegister c?, Regis?(c?)
  putDAC Regis?(c?), Settings?(c?, 0), Settings?(c?, 1), Settings?(c?, 2)
NEXT c?

DO: LOOP WHILE INKEY$=""
SCREEN 0
END

'======================================================================
SUB SetRegister(BYVAL Attribute?, BYVAL Register?)

  ASM mov ax, &H1000       ; function 10h, subfunction 00h
  ASM mov bh, Register?    ; register to set
  ASM mov bl, Attribute?   ; attribute to set
  ASM int &H10             ; call BIOS services

END SUB


' Which DAC Register Is Used for each Attribute
FUNCTION WhichRegister?(BYVAL Register?)

  ASM mov ax, &H1007       ; function 10h, subfunction 07h
  ASM mov bl, Register?    ; register to check
  ASM int &H10             ; call BIOS services
  ASM mov FUNCTION, bh     ; set return value of function

END FUNCTION

SUB putDAC (ind?, red?, green?, blue?)
'Sets new RGB values in the VGA palette for color no. ind%

REG 1, &H1010
REG 2, ind?
REG 3, 256*green? + blue?
REG 4, 256*red?
CALL INTERRUPT &H10
END SUB

SUB getDAC (ind?, red?, green?, blue?)
'Retrieves the RGB values of the current VGA palette for color no. ind%

REG 1, &H1015
REG 2, ind?
CALL INTERRUPT &H10
gb% = REG(3)
green? = gb%\256: blue? = gb% AND 255
red? = REG(4)\256
END SUB

'============================================================

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