Shareware Overload/ShartewareOverload.cdr/games/egagraph.zip/LINE.ASM

Assembly Source File | 1987-07-23 | 5KB | 182 lines

; LINE.ASM   EGA line drawing routine

; PROCEDURE DrawLine(x1,y1,x2,y2,color : integer); External 'LINE.BIN';

; This routine is designed to be called from Turbo Pascal.
; It has been tested on both EGA and 640x480 modes on the
; Video 7 graphics board. This routine draws at about 84,000
; pixels per second on a 10 mhz, 1 wait state, 286 machine.
; If you find a way to make it faster, let me know.

; James Billmeyer
; Soft-Touch Computer Systems
; 7716 Balboa Blvd., Unit D
; Van Nuys, Ca. 91406
; [phone]

cseg   segment  byte              ; start of code segment
       assume   cs:cseg

; [bp-2]  = xinc
; [bp-4]  = yinc1
; [bp-6]  = yinc2
; [bp-8]  = incr1
; [bp-10] = incr2

; AX = general use
; BL = Mask
; BH = Color
; CX = delx (or longest dela length -- main loop only)
; DX = (for port output)
; DI = Address
; SI = d

line   proc     near

; --- Initialization ---

       int    1
       push   bp
       mov    bp,sp          ; get top of stack
       sub    sp,10          ; allow for variable space

       mov    ax,80
       mov    [bp-6],ax      ; yinc2 := 80
       mov    [bp-4],ax      ; yinc1 := 80
       mov    ax,1
       mov    [bp-2],ax      ; xinc  := 1
       mov    ax,[bp+8]      ; delx := x2 - x1
       sub    ax,[bp+12]
       cmp    ax,0           ; if delx < 0 then
       jge    cdely
       neg    ax             ;   delx := abs(delx)
       mov    bx,[bp+8]      ;   x1   := x2
       mov    [bp+12],bx
       mov    bx,[bp+6]      ;   swap(y2,y1)
       xchg   bx,[bp+10]
       mov    [bp+6],bx      ; endif

cdely:
       mov    bx,[bp+6]      ; dely := y2 - y1
       sub    bx,[bp+10]
       cmp    bx,0
       jge    cmpdxdy        ; else if dely < 0 then
       neg    bx             ;   dely  := abs(dely)
       mov    dx,-80         ;   yinc2 := -80
       mov    [bp-6],dx
       mov    [bp-4],dx      ; endif

cmpdxdy:
       cmp    ax,bx          ; if delx < dely then
       jge    setyinc1
       mov    dx,0           ;   xinc := 0
       mov    [bp-2],dx
       xchg   ax,bx          ;   swap(delx,dely);
       jmp    calcaddr       ; else
setyinc1:
       mov    dx,0           ;   yinc1 := 0
       mov    [bp-4],dx
                             ; endif
calcaddr:
       push   ax
       mov    cx,bx          ; incr1 := dely * 2
       shl    cx,1
       mov    [bp-8],cx
       sub    bx,ax          ; incr2 := (dely - delx) * 2
       shl    bx,1
       mov    [bp-10],bx
       mov    si,bx
       mov    ax,[bp+10]     ; address := (y * 80) + (x / 8)
       mov    dx,80
       mul    dx
       mov    cx,3
       mov    di,[bp+12]
       shr    di,cl
       add    di,ax
       mov    cx,[bp+12]     ; mask := 1 shl (7 - x mod 8)
       and    cl,7
       xor    cl,7
       mov    ch,1
       shl    ch,cl
       mov    bl,ch

; ---- Initialize EGA Card ----
; Select Write Mode 2

       mov    dx,3CEh        ; select mode register
       mov    ax,5
       out    dx,al
       mov    dx,3CFh        ; set to write mode 2
       mov    ax,2
       out    dx,al

; Set Bit Mask Register

       mov    dx,3CEh        ; select register 8
       mov    ax,8
       out    dx,al
       mov    dx,0A000h      ;    es := EGA buffer segment address
       mov    es,dx
       mov    bh,[bp+4]      ;    get color
       mov    dx,3CFh

       pop    cx             ; for i := 1 to dx do
       inc    cx
llp1:

; ---- Plot Point -------------+
                             ; |
       mov    al,bl          ; | output bit mask to register 8
       out    dx,al          ; |
                             ; |
; Latch all four bit planes  ; |
                             ; |
       mov    al,es:[di]     ; | latches all four bit planes
                             ; |
; Write Pixel                ; |
                             ; |
       mov    es:[di],bh     ; | set color
                             ; |
; --- end of plot point -------+

       cmp    si,0           ;   if d < 0 then
       jge    llp2
       mov    ax,cx
       mov    cx,[bp-2]      ;     x := x + xinc1
       ror    bl,cl
       mov    cx,ax
       adc    di,+00
       add    di,[bp-4]      ;     y := y + yinc1
       add    si,[bp-8]      ;     d := d + incr1
       loop   llp1
       jmp    lend
llp2:                        ;   else
       ror    bl,1           ;     x := x + xinc2
       adc    di,+00
       add    di,[bp-6]      ;     y := y + yinc2
       add    si,[bp-10]     ;     d := d + incr2
       loop   llp1           ;   endif
                             ; endfor
lend:

; Restore defualt EGA graphics status

       mov    dx,3CEh
       mov    ax,5
       out    dx,al
       mov    dx,3CFh
       mov    ax,0
       out    dx,al
       mov    dx,3CEh
       mov    ax,8
       out    dx,al
       mov    dx,3CFh
       mov    ax,0FFh
       out    dx,al
       mov    sp,bp
       pop    bp
       ret    10
line   endp
cseg   ends
       end