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Index > OS Construction > most efficient way of change background color in textmode?

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Joined: 03 Mar 2006
Posts: 23
if it is the way of change the background color int text mode that I have found

AH = 0Bh
BH = 00h
BL = background/border color (border only in text modes)
Return: nothing
SeeAlso: AH=0Bh/BH=01h

then i tried to do this in debug to see how it works

mov ah,0xb
mov bh,0
mov bl,0x70
int 0x10    

but it doesn't change the bg color, the docs that i have doesn't specify the format of the value that is passed to BL

Tah rah rah boom de ay, I blew some guy away, his brains turned into spray, I was paid well that day
Post 14 Mar 2006, 19:40
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Joined: 15 Mar 2005
Posts: 4
I signed up for this board a long time never came back till now, anyway, that's besides the point, I don't know if there is a better way, but for text color mode, the address in memory for the video buffer is at B8000h and the buffer is an array of words, the high byte being the backcolor and forecolor and the low byte being the character for the screen. The high nibble of the high byte is the backcolor and the low nibble is the forecolor. since you got 80x25 I'm guessing, it would be comprised of 2000 words aka 4000 bytes. the colors for the nibbles are gonna be below in the code I'm gonna post. basicly you would have to know where the last word is (2000 * 2) - 2 and either count up or down and change the back color, a good AND will null the backcolor and OR will write the back color anyway here's the code

;; Input: SI = Color        ;;
;; Colors:                  ;;
;;         0 black          ;;
;;         1 blue           ;;
;;         2 green          ;;
;;         3 cyan           ;;
;;         4 red            ;;
;;         5 magenta        ;;
;;         6 brown          ;;
;;         7 light gray     ;;
;;         8 dark gray      ;;
;;         9 light blue     ;;
;;         10 light green   ;;
;;         11 light cyan    ;;
;;         12 light red     ;;
;;         13 light magenta ;;
;;         14 light brown   ;;
;;         15 white         ;;
  ;; save data segment
  push ds
  ;; save the regs not sure if you need them
  ;; setup the segment
  mov ax, 0B800h
  mov ds, ax
  ;; last byte of video buffer for 80x25
  mov di, 3998
  ;; shift color to backcolor in high nibble of the high byte
  shl si, 12
  ;; null the backcolor, high nibble of high byte
  and word [di], 0FFFh
  ;; set the backcolor
  or word [ds:di], si
  ;; decrease di by 2, point to next word in array
  sub di, 2
  ;; jump if not signed, greater then or equal to zero to @@
  jns @r
  ;; restore previous register values
  ;; restore data segment
  pop ds

as for the int, I think the way it's read as you can only change the border color in text mode, which I think would be the low nibble of bl, I'm not sure how to use it, as I write my own graphic functions but might try it later, I did test this code and it works on 80x25 color text mode.

Post 15 Mar 2006, 15:47
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