Category : Files from Magazines
Archive   : PJ-VGA.ZIP
Filename : VGA62-L2.ASM

 
Output of file : VGA62-L2.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 2 ***
;
; Program to illustrate one use of write mode 2 of the VGA and EGA by
; drawing lines in color patterns.
;
; 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
GRAPHICS_SEGMENT equ 0a000h ;mode 10 bit-map segment
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'
Pattern0 db 16
db 0, 1, 2, 3, 4, 5, 6, 7, 8
db 9, 10, 11, 12, 13, 14, 15
Pattern1 db 6
db 2, 2, 2, 10, 10, 10
Pattern2 db 8
db 15, 15, 15, 0, 0, 15, 0, 0
Pattern3 db 9
db 1, 1, 1, 2, 2, 2, 4, 4, 4
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)
;
; Draw 8 radial lines in upper left quadrant in pattern 0.
;
mov bx,0
mov cx,0
mov si,offset Pattern0
call QuadrantUp
;
; Draw 8 radial lines in upper right quadrant in pattern 1.
;
mov bx,320
mov cx,0
mov si,offset Pattern1
call QuadrantUp
;
; Draw 8 radial lines in lower left quadrant in pattern 2.
;
mov bx,0
mov cx,175
mov si,offset Pattern2
call QuadrantUp
;
; Draw 8 radial lines in lower right quadrant in pattern 3.
;
mov bx,320
mov cx,175
mov si,offset Pattern3
call QuadrantUp
;
; 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
;
; Draws 8 radial lines with specified pattern in specified mode 10h
; quadrant.
;
; Input:
; BX = X coordinate of upper left corner of quadrant
; CX = Y coordinate of upper left corner of quadrant
; SI = pointer to pattern, in following form:
; Byte 0: Length of pattern
; Byte 1: Start of pattern, one color per byte
;
; AX, BX, CX, DX destroyed
;
QuadrantUp proc near
add bx,160
add cx,87 ;point to the center of the quadrant
mov ax,0
mov dx,160
call LineUp ;draw horizontal line to right edge
mov ax,1
mov dx,88
call LineUp ;draw diagonal line to upper right
mov ax,2
mov dx,88
call LineUp ;draw vertical line to top edge
mov ax,3
mov dx,88
call LineUp ;draw diagonal line to upper left
mov ax,4
mov dx,161
call LineUp ;draw horizontal line to left edge
mov ax,5
mov dx,88
call LineUp ;draw diagonal line to lower left
mov ax,6
mov dx,88
call LineUp ;draw vertical line to bottom edge
mov ax,7
mov dx,88
call LineUp ;draw diagonal line to bottom right
ret
QuadrantUp endp
;
; Draws a horizontal, vertical, or diagonal line (one of the eight
; possible radial lines) of the specified length from the specified
; starting point.
;
; Input:
; AX = line direction, as follows:
; 3 2 1
; 4 * 0
; 5 6 7
; BX = X coordinate of starting point
; CX = Y coordinate of starting point
; DX = length of line (number of pixels drawn)
;
; All registers preserved.
;
; Table of vectors to routines for each of the 8 possible lines.
;
LineUpVectors label word
dw LineUp0, LineUp1, LineUp2, LineUp3
dw LineUp4, LineUp5, LineUp6, LineUp7

;
; Macro to draw horizontal, vertical, or diagonal line.
;
; Input:
; XParm = 1 to draw right, -1 to draw left, 0 to not move horz.
; YParm = 1 to draw up, -1 to draw down, 0 to not move vert.
; BX = X start location
; CX = Y start location
; DX = number of pixels to draw
; DS:SI = line pattern
;
MLineUp macro XParm, YParm
local LineUpLoop, CheckMoreLine
mov di,si ;set aside start offset of pattern
lodsb ;get length of pattern
mov ah,al

LineUpLoop:
lodsb ;get color of this pixel...
call DotUpInColor ;...and draw it
if XParm EQ 1
inc bx
endif
if XParm EQ -1
dec bx
endif
if YParm EQ 1

inc cx
endif
if YParm EQ -1
dec cx
endif
dec ah ;at end of pattern?
jnz CheckMoreLine
mov si,di ;get back start of pattern
lodsb
mov ah,al ;reset pattern count

CheckMoreLine:
dec dx
jnz LineUpLoop
jmp LineUpEnd
endm

LineUp proc near
push ax
push bx
push cx
push dx
push si
push di
push es

mov di,ax

mov ax,GRAPHICS_SEGMENT
mov es,ax

push dx ;save line length
;
; Enable writes to all planes.
;
mov dx,SC_INDEX
mov al,MAP_MASK
out dx,al
inc dx
mov al,0fh
out dx,al
;
; Select write mode 2.
;
mov dx,GC_INDEX
mov al,GRAPHICS_MODE
out dx,al
inc dx
mov al,02h
out dx,al
;
; Vector to proper routine.
;
pop dx ;get back line length

shl di,1
jmp cs:[LineUpVectors+di]
;
; Horizontal line to right.
;
LineUp0:
MLineUp 1, 0
;
; Diagonal line to upper right.
;
LineUp1:
MLineUp 1, -1
;
; Vertical line to top.
;
LineUp2:
MLineUp 0, -1
;
; Diagonal line to upper left.
;
LineUp3:
MLineUp -1, -1
;
; Horizontal line to left.
;
LineUp4:
MLineUp -1, 0
;
; Diagonal line to bottom left.
;
LineUp5:
MLineUp -1, 1
;
; Vertical line to bottom.
;
LineUp6:
MLineUp 0, 1
;
; Diagonal line to bottom right.
;
LineUp7:
MLineUp 1, 1

LineUpEnd:
pop es
pop di
pop si
pop dx
pop cx
pop bx
pop ax
ret
LineUp endp
;
; Draws a dot in the specified color at the specified location.
; Assumes that the VGA is in write mode 2 with writes to all planes
; enabled and that ES points to display memory.
;
; Input:
; AL = dot color
; BX = X coordinate of dot
; CX = Y coordinate of dot
; ES = display memory segment
;
; All registers preserved.
;
DotUpInColor proc near
push bx
push cx
push dx
push di
;
; Point ES:DI to the display memory byte in which the pixel goes, with
; the bit mask set up to access that pixel within the addressed byte.
;
push ax ;preserve dot color
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 dx,GC_INDEX
mov al,BIT_MASK
out dx,al
inc dx
mov al,80h
shr al,cl
out dx,al ;set the bit mask for the pixel
shr bx,1
shr bx,1
shr bx,1 ;X in bytes
add di,bx ;offset of byte pixel is in
mov al,es:[di] ;load latches
pop ax ;get back dot color
stosb ;write dot in desired color

pop di
pop dx
pop cx
pop bx
ret
DotUpInColor endp
Start endp
Code ends
end Start



  3 Responses to “Category : Files from Magazines
Archive   : PJ-VGA.ZIP
Filename : VGA62-L2.ASM

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

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