; Highway by Solar Designer \\ BPC 

Program Highway
.186

MinY =   136       ; Only MaxY-MinY is used in this simplified version
MaxY =   199       ; Also, MaxY-MinY should be equal to 63 in this version
PosY =   16        ; Position at which the road is motionless
MinW =   32        ; Road width at top
MaxW =   MinW+256  ; Road width at bottom, should be MinW+256 in this version
CosMax = 79h

mov  al,13h        ; Hope noone will run it with invalid drive as the
int  10h           ; second command line parameter ;)

push 0A000h        ; Set up both ES and DS to point to the video memory
pop  es            ; The shifts array at 0A000h:0FA00h is assumed to be
push es            ; zeroed out when setting the video mode
pop  ds
mov  di,Shifts-(MaxY-MinY)*320    ; DI will point to the shifts array after
                                  ; the loop below

mov  ch,78h        ; Initialize the sine generator, value in CL is not
                   ; important, BX is assumed to contain zero here
$Do
   pusha

   mov  bx,Shifts+2*(MaxY-MinY)   ; DS:BX -> shifts array end
   $Do
; Set SI to current road width divided by -2
      lea  si,[bx-(Shifts + 2*(MaxY-MinY) + MinW/2)]

      mov  bp,160                 ; Screen center
      add  bp,ds:[bx]             ; ...add current shift
      sub  bp,ds:[Shifts+2*PosY]  ; ...subtract motionless position shift
      lea  cx,[si+bp]             ; Current road left edge's position
      xchg ax,si
      lea  si,[di+bp]             ; Current mark's memory offset
      sub  bp,ax                  ; Current road right edge's position
      imul ax,-2                  ; Real current road width
      push ax

      mov  al,7                   ; Draw the background's left
      rep  stosb

      pop  cx
      inc  ax
      rep  stosb                  ; Draw one horizontal line of the road

      mov  cx,320
      sub  cx,bp
      dec  ax
      inc  dx
      test dl,8                   ; Are we drawing a mark?
      $If <>0
         mov  ds:[si],al          ; Draw it
      $EndIf
      rep  stosb                  ; Draw the background's right

      sub  bl,2                   ; Move to the next horizontal line
   $EndDo =0

   mov  si,Shifts + 2             ; DI already points to the shifts array
   mov  cl,MaxY-MinY
   rep  movsw                     ; Move the road's shifts

   popa

   dec  dx                        ; Move the marks
   push dx

   mov  ax,-39                    ; Calculate a new shift
   imul cx                        ; I use a modification of sine generator
   add  bx,dx                     ; by Wally/RAGE here
   add  cx,bx
   mov  ax,cx
   sar  ax,8+2
   sub  ax,CosMax shr 2           ; Make it always negative
   mov  word ptr ds:[Shifts+2*(MaxY-MinY)],ax

   mov  dx,3DAh                   ; Wait for vertical retrace to make the
   $Do                            ; intro run at a reasonable speed on
      in   al,dx                  ; fast video cards
      test al,8
   $EndDo <>0

   pop  dx

   in   al,60h                    ; Read a scan code
   cbw                            ; Zero out AH for use by INT 10h below
   dec  ax                        ; Exit on Escape
$EndDo =0

mov  al,3                         ; Restore the text mode
int  10h

retn                              ; Exit

db   'Solar!'                     ;-)

Shifts = 320*200