Category : Files from Magazines
Archive   : PWRGRPHC.ZIP
Filename : CHAP09.3

; Program to illustrate the color mapping capabilities of the
; EGA's palette registers.
;
; Updated 6/29/89.
;
VGA_SEGMENT equ 0a000h
SC_INDEX equ 3c4h ;Sequence Controller Index register
MAP_MASK equ 2 ;Map Mask register index in SC
BAR_HEIGHT equ 14 ;height of each bar
TOP_BAR equ BAR_HEIGHT*6 ;start the bars down a bit to
; leave room for text
;
stackseg segment para stack 'STACK'
db 512 dup (?)
stackseg ends
;
Data segment word 'DATA'
KeyMsg db 'Press any key to see the next color set. '
db 'There are 64 color sets in all.'
db 0dh, 0ah, 0ah, 0ah, 0ah
db 13 dup (' '), 'Attribute'
db 38 dup (' '), 'Color$'
;
; Used to label the attributes of the color bars.
;
AttributeNumbers label byte
x= 0
rept 16
if x lt 10
db '0', x+'0', 'h', 0ah, 8, 8, 8
else
db '0', x+'A'-10, 'h', 0ah, 8, 8, 8
endif
x= x+1
endm
db '$'
;
; Used to label the colors of the color bars. (Color values are
; filled in on the fly.)
;
ColorNumbers label byte
rept 16
db '000h', 0ah, 8, 8, 8, 8
endm
COLOR_ENTRY_LENGTH equ ($-ColorNumbers)/16
db '$'
;
CurrentColor db ?
;
; Space for the array of 16 colors we'll pass to the BIOS, plus
; an overscan setting of black.
;
ColorTable db 16 dup (?), 0
Data ends
;
Code segment
assume cs:Code, ds:Data
Start proc near
cld
mov ax,Data
mov ds,ax
;
; Go to hi-res graphics mode.
;
mov ax,10h ;AH = 0 means mode set, AL = 10h selects
; hi-res graphics mode
int 10h ;BIOS video interrupt
;
; Put up relevant text.
;
mov ah,9 ;DOS print string function
mov dx,offset KeyMsg
int 21h
;
; Put up the color bars, one in each of the 16 possible pixel values
; (which we'll call attributes).
;
mov cx,16 ;we'll put up 16 color bars
sub al,al ;start with attribute 0
BarLoop:
push ax
push cx
call BarUp
pop cx
pop ax
inc ax ;select the next attribute
loop BarLoop
;
; Put up the attribute labels.
;
mov ah,2 ;video interrupt set cursor position function
sub bh,bh ;page 0
mov dh,TOP_BAR/14 ;counting in character rows, match to
; top of first bar, counting in
; scan lines
mov dl,16 ;just to left of bars
int 10h
mov ah,9 ;DOS print string function
mov dx,offset AttributeNumbers
int 21h
;
; Loop through the color set, one new setting per keypress.
;
mov [CurrentColor],0 ;start with color zero
ColorLoop:
;
; Set the palette registers to the current color set, consisting
; of the current color mapped to attribute 0, current color + 1
; mapped to attribute 1, and so on.
;
mov al,[CurrentColor]
mov bx,offset ColorTable
mov cx,16 ;we have 16 colors to set
PaletteSetLoop:
and al,3fh ;limit to 6-bit color values
mov [bx],al ;built the 16-color table used for setting
inc bx ; the palette registers
inc ax
loop PaletteSetLoop
mov ah,10h ;video interrupt palette function
mov al,2 ;subfunction to set all 16 palette registers
; and overscan at once
mov dx,offset ColorTable
push ds
pop es ;ES:DX points to the color table
int 10h ;invoke the video interrupt to set the palette
;
; Put up the color numbers, so we can see how attributes map

; to color values, and so we can see how each color # looks
; (at least on this particular screen).
;
call ColorNumbersUp
;
; Wait for a keypress, so they can see this color set.
;
WaitKey:
mov ah,8 ;DOS input without echo function
int 21h
;
; Advance to the next color set.
;
mov al,[CurrentColor]
inc ax
mov [CurrentColor],al
cmp al,64
jbe ColorLoop
;
; Do a mode set to restore text mode to its default state.
;
mov ax,3
int 10h
;
; Done.
;
Done:
mov ah,4ch ;DOS terminate function
int 21h
;
; Puts up a bar consisting of the specified attribute (pixel value),
; at a vertical position corresponding to the attribute.
;
; Input: AL = attribute
;
BarUp proc near
mov dx,SC_INDEX
mov ah,al
mov al,MAP_MASK
out dx,al
inc dx
mov al,ah
out dx,al ;set the Map Mask register to produce
; the desired color
mov ah,BAR_HEIGHT
mul ah ;row of top of bar
add ax,TOP_BAR ;start a few lines down to leave room for
; text
mov dx,80 ;rows are 80 bytes long
mul dx ;offset in bytes of start of scan line bar
; starts on
add ax,20 ;offset in bytes of upper left corner of bar
mov di,ax
mov ax,VGA_SEGMENT
mov es,ax ;ES:DI points to offset of upper left
; corner of bar
mov dx,BAR_HEIGHT
mov al,0ffh
BarLineLoop:
mov cx,40 ;make the bars 40 wide
rep stosb ;do one scan line of the bar
add di,40 ;point to the start of the next scan line
; of the bar
dec dx
jnz BarLineLoop
ret
BarUp endp
;
; Converts AL to a hex digit in the range 0-F.
;
BinToHexDigit proc near
cmp al,9
ja IsHex
add al,'0'
ret
IsHex:
add al,'A'-10
ret
BinToHexDigit endp
;
; Displays the color values generated by the color bars given the
; current palette register settings off to the right of the color
; bars.
;
ColorNumbersUp proc near
mov ah,2 ;video interrupt set cursor position function
sub bh,bh ;page 0
mov dh,TOP_BAR/14 ;counting in character rows, match to
; top of first bar, counting in
; scan lines
mov dl,20+40+1 ;just to right of bars
int 10h
mov al,[CurrentColor] ;start with the current color
mov bx,offset ColorNumbers+1
;build the color number text string on the fly
mov cx,16 ;we've got 16 colors to do
ColorNumberLoop:
push ax ;save the color #
and al,3fh ;limit to 6-bit color values
shr al,1
shr al,1
shr al,1
shr al,1 ;isolate the high nibble of the
; color #
call BinToHexDigit ;convert the high color # nibble
mov [bx],al ; and put it into the text
pop ax ;get back the color #
push ax ;save the color #
and al,0fh ;isolate the low color # nibble
call BinToHexDigit ;convert the low nibble of the
; color # to ASCII
mov [bx+1],al ; and put it into the text
add bx,COLOR_ENTRY_LENGTH ;point to the next entry
pop ax ;get back the color #
inc ax ;next color #
loop ColorNumberLoop
mov ah,9 ;DOS print string function
mov dx,offset ColorNumbers
int 21h ;put up the attribute numbers
ret
ColorNumbersUp endp
;
Start endp
Code ends
end Start