;Warning!
;mousedr.asm
.model tiny
.code
org 100h
.186
start:
      mov       ax, 12h ;X 12h+80h X
      int       10h
      mov       ax, 0
      int       33h
      mov       ax, 1
      int       33h

      mov       ax, 000Ch
      mov       cx, 0002h
      mov       dx, offset handler
      int       33h

      mov       ah, 0
      int       16h
      mov       ax, 000Ch
      mov       cx, 0000h
      int       33h
      mov       ax, 83h
      int       10h
      ret
; Обработчик событий от мыши
handler:
      push      0A000h
      pop       es
      push      cs
      pop       ds
      push      cx
      push      dx

      mov       ax, 2
      int       33h

      cmp       word ptr previous_X, -1
      je        first_point

      call      line_bresenham
exit_handler:
      pop    dx
      pop    cx
      mov    previous_X, cx
      mov    previous_Y, dx

      mov    ax, 1
      int    33h

      retf

first_point:
      call   putpixel1b
      jmp    short exit_handler

;Процедура рисования прямой линии
line_bresenham:
      mov      ax, cx
      sub      ax, previous_X
      jns      dx_pos
      neg      ax
      mov      word ptr X_increment, 1
      jmp      short dx_neg
dx_pos:
      mov      word ptr X_increment, -1

dx_neg:
      mov       bx, dx
      sub       bx, previous_Y
      jns       dy_pos
      neg       bx
      mov       word ptr Y_increment, 1
      jmp       short dy_neg
dy_pos:
      mov       word ptr Y_increment, -1
dy_neg:
      shl       ax, 1
      shl       bx, 1

      call      putpixel1b

      cmp       ax, bx
      jna       dx_le_dy
      mov       di, ax
      shr       di, 1
      neg       di
      add       di, bx
cycle:
      cmp       cx, word ptr previous_X
      je        exit_bres
      cmp       di, 0
      jl        fractlt0
      add       dx, word ptr Y_increment
      sub       di, ax
fractlt0:
      add       cx, word ptr X_increment
      add       di, bx
      call      putpixel1b
      jmp       short     cycle

dx_le_dy:
      mov       di, bx
      shr       di, 1
      neg       di
      add       di, ax
cycle2:
      cmp       dx, word ptr previous_Y
      je        exit_bres
      cmp       di, 0
      jl        fractlt02
      add       cx, word ptr X_increment
      sub       di, bx
fractlt02:
      add       dx, word ptr Y_increment
      add       di, ax
      call      putpixel1b
      jmp       short cycle2
exit_bres:
      ret
; Процедура вывода точки на экран
putpixel1b:
      pusha
      xor       bx, bx
      mov       ax, dx
      imul      ax, ax, 80
      push      cx
      shr       cx, 3
      add       ax, cx
      mov       di, ax
      mov       si, di

      pop       cx
      mov       bx, 0080h
      and       cx, 07h

      shr       bx, cl
      lods      es:byte ptr some_label
      or        ax, bx
      stosb
      popa
      ret

previous_X      dw      -1
previous_Y      dw      -1
Y_increment     dw      -1
X_increment     dw      -1

some_label:

           end  start

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