Category : Files from Magazines
Archive   : PJ-VGA.ZIP
Filename : VGA62-L1.ASM

 
Output of file : VGA62-L1.ASM contained in archive : PJ-VGA.ZIP
Code from "Yet Another VGA Write Mode" by Michael Abrash, PJ,
Volume 6.2. Copyright 1987 Michael Abrash
;
; *** Listing 1 ***
;
; Program to illustrate one use of write mode 2 of the VGA and EGA by
; animating the image of an "A" drawn by copying it from a chunky
; bit-map in system memory to a planar bit-map in VGA or EGA memory.
;
; Assembled with MASM 5.0, linked with MS-LINK 3.60.
;
; By Michael Abrash 11/8/87
;
Stack segment para stack 'STACK'
db 512 dup(0)
Stack ends

SCREEN_WIDTH_IN_BYTES equ 80
DISPLAY_MEMORY_SEGMENT equ 0a000h
SC_INDEX equ 3c4h ;Sequence Controller Index register
MAP_MASK equ 2 ;index of Map Mask register
GC_INDEX equ 03ceh ;Graphics Controller Index reg
GRAPHICS_MODE equ 5 ;index of Graphics Mode reg
BIT_MASK equ 8 ;index of Bit Mask reg

Data segment para common 'DATA'
;
; Current location of "A" as it is animated across the screen.
;
CurrentX dw ?
CurrentY dw ?
RemainingLength dw ?
;
; Chunky bit-map image of a yellow "A" on a bright blue background
;
AImage label byte
dw 13, 13 ;width, height in pixels
db 000h, 000h, 000h, 000h, 000h, 000h, 000h
db 009h, 099h, 099h, 099h, 099h, 099h, 000h
db 009h, 099h, 099h, 099h, 099h, 099h, 000h
db 009h, 099h, 099h, 0e9h, 099h, 099h, 000h
db 009h, 099h, 09eh, 0eeh, 099h, 099h, 000h
db 009h, 099h, 0eeh, 09eh, 0e9h, 099h, 000h
db 009h, 09eh, 0e9h, 099h, 0eeh, 099h, 000h
db 009h, 09eh, 0eeh, 0eeh, 0eeh, 099h, 000h
db 009h, 09eh, 0e9h, 099h, 0eeh, 099h, 000h
db 009h, 09eh, 0e9h, 099h, 0eeh, 099h, 000h
db 009h, 099h, 099h, 099h, 099h, 099h, 000h
db 009h, 099h, 099h, 099h, 099h, 099h, 000h
db 000h, 000h, 000h, 000h, 000h, 000h, 000h
Data ends

Code segment para public 'CODE'
assume cs:Code, ds:Data
Start proc near
mov ax,Data
mov ds,ax
mov ax,10h
int 10h ;select video mode 10h (640x350)
;
; Prepare for animation.
;
mov [CurrentX],0
mov [CurrentY],200
mov [RemainingLength],600 ;move 600 times
;
; Animate, repeating RemainingLength times. It's unnecessary to erase
; the old image, since the one pixel of blank fringe around the image
; erases the part of the old image not overlapped by the new image.
;
AnimationLoop:
mov bx,[CurrentX]
mov cx,[CurrentY]
mov si,offset AImage
call DrawFromChunkyBitmap ;draw the "A" image
inc [CurrentX] ;move one pixel to the right
dec [RemainingLength]
jnz AnimationLoop
;
; Wait for a key before returning to text mode and ending.
;
mov ah,01h
int 21h
mov ax,03h
int 10h
mov ah,4ch
int 21h
Start endp
;
; Draw an image stored in a chunky-bit map into planar VGA/EGA memory
; at the specified location.
;
; Input:
; BX = X screen location at which to draw the upper left corner
; of the image
; CX = Y screen location at which to draw the upper left corner
; of the image
; DS:SI = pointer to chunky image to draw, as follows:
; word at 0: width of image, in pixels
; word at 2: height of image, in pixels
; byte at 4: msb/lsb = first & second chunky pixels,
; repeating for the remainder of the scan line
; of the image, then for all scan lines. Images
; with odd widths have an unused null nibble
; padding each scan line out to a byte width
;
; AX, BX, CX, DX, SI, DI, ES destroyed.
;
DrawFromChunkyBitmap proc near
cld
;
; Select write mode 2.
;
mov dx,GC_INDEX
mov al,GRAPHICS_MODE
out dx,al
inc dx
mov al,02h
out dx,al
;
; Enable writes to all 4 planes.
;
mov dx,SC_INDEX
mov al,MAP_MASK
out dx,al
inc dx
mov al,0fh
out dx,al
;
; Point ES:DI to the display memory byte in which the first pixel
; of the image goes, with AH set up as the bit mask to access that
; pixel within the addressed byte.
;
mov ax,SCREEN_WIDTH_IN_BYTES
mul cx ;offset of start of top scan line
mov di,ax
mov cl,bl
and cl,111b
mov ah,80h ;set AH to the bit mask for the
shr ah,cl ; initial pixel
shr bx,1
shr bx,1
shr bx,1 ;X in bytes
add di,bx ;offset of upper left byte of image
mov bx,DISPLAY_MEMORY_SEGMENT
mov es,bx ;ES:DI points to the byte at which the
; upper left of the image goes
;
; Get the width and height of the image.
;
mov cx,[si] ;get the width
inc si
inc si
mov bx,[si] ;get the height
inc si
inc si
mov dx,GC_INDEX
mov al,BIT_MASK
out dx,al ;leave the GC Index register pointing
inc dx ; to the Bit Mask register
RowLoop:

push ax ;preserve the left column's bit mask
push cx ;preserve the width
push di ;preserve the destination offset

ColumnLoop:
mov al,ah
out dx,al ;set the bit mask to draw this pixel
mov al,es:[di] ;load the latches
mov al,[si] ;get the next two chunky pixels
shr al,1
shr al,1
shr al,1
shr al,1 ;move the first pixel into the lsb
stosb ;draw the first pixel
ror ah,1 ;move mask to next pixel position
jc CheckMorePixels ;is next pixel in the adjacent byte?
dec di ;no

CheckMorePixels:
dec cx ;see if there are any more pixels
jz AdvanceToNextScanLine ; across in image
mov al,ah
out dx,al ;set the bit mask to draw this pixel
mov al,es:[di] ;load the latches
lodsb ;get the same two chunky pixels again
; and advance pointer to the next
; two pixels
stosb ;draw the second of the two pixels
ror ah,1 ;move mask to next pixel position
jc CheckMorePixels2 ;is next pixel in the adjacent byte?
dec di ;no

CheckMorePixels2:
loop ColumnLoop ;see if there are any more pixels
; across in the image
jmp short CheckMoreScanLines

AdvanceToNextScanLine:
inc si ;advance to the start of the next
; scan line in the image

CheckMoreScanLines:
pop di ;get back the destination offset
pop cx ;get back the width
pop ax ;get back the left column's bit mask
add di,SCREEN_WIDTH_IN_BYTES
;point to the start of the next scan
; line of the image
dec bx ;see if there are any more scan lines
jnz RowLoop ; in the image
ret
DrawFromChunkyBitmap endp
Code ends
end Start



  3 Responses to “Category : Files from Magazines
Archive   : PJ-VGA.ZIP
Filename : VGA62-L1.ASM

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