在下面的红色部分的那句代码中就是_CreateClockPic子程序调用bitblt函数的参数中有两个句柄源设备句柄和目的设备句柄他们并没有被赋值为什么可以正常工作？谢谢！！！
.386
.model flat, stdcall
option casemap :none

include windows.inc
include user32.inc
includelib user32.lib
include kernel32.inc
includelib kernel32.lib
include Gdi32.inc
includelib Gdi32.lib

; 常量定义
CLOCK_SIZE equ 150
ICO_MAIN equ 100
IDC_MAIN equ 100
IDC_MOVE equ 101
IDB_BACK1 equ 100
IDB_CIRCLE1 equ 101
IDB_MASK1 equ 102
IDB_BACK2 equ 103
IDB_CIRCLE2 equ 104
IDB_MASK2 equ 105
ID_TIMER equ 1
IDM_BACK1 equ 100
IDM_BACK2 equ 101
IDM_CIRCLE1 equ 102
IDM_CIRCLE2 equ 103
IDM_EXIT equ 104

; 数据段定义
.data?
hInstance dd ?
hWinMain dd ?
hCursorMove dd ?
hCursorMain dd ?
hMenu dd ?
hBmpBack dd ?
hDcBack dd ?
hBmpClock dd ?
hDcClock dd ?
dwNowBack dd ?
dwNowCircle dd ?

; 数据段常量定义
.const
szClassName db 'Clock',0
dwPara180 dw 180
dwRadius dw CLOCK_SIZE/2
szMenuBack1 db '使用格子背景(&A)',0
szMenuBack2 db '使用花布背景(&B)',0
szMenuCircle1 db '使用淡蓝色边框(&C)',0
szMenuCircle2 db '使用粉红色边框(&D)',0
szMenuExit db '退出(&X)...',0

; 代码段
.code
; 计算时钟圆周上某个角度对应的 X 坐标
; X = 圆心X + Sin(角度) * 半径
_CalcX proc _dwDegree,_dwRadius
local @dwReturn
fild dwRadius
fild _dwDegree
fldpi
fmul ;角度*Pi
fild dwPara180
fdivp st(1),st ;角度*Pi/180
fsin ;Sin(角度*Pi/180)
fild _dwRadius
fmul ;半径*Sin(角度*Pi/180)
fadd ;X+半径*Sin(角度*Pi/180)
fistp @dwReturn
mov eax,@dwReturn
ret
_CalcX endp

; 计算时钟圆周上某个角度对应的 Y 坐标
; Y = 圆心Y - Cos(角度) * 半径
_CalcY proc _dwDegree,_dwRadius
local @dwReturn
fild dwRadius
fild _dwDegree
fldpi
fmul
fild dwPara180
fdivp st(1),st
fcos
fild _dwRadius
fmul
fsubp st(1),st
fistp @dwReturn
mov eax,@dwReturn
ret
_CalcY endp

; 画 _dwDegree 角度的线条，半径=_dwRadius
_DrawLine proc _hDC,_dwDegree,_dwRadius
local @dwX1,@dwY1,@dwX2,@dwY2
invoke _CalcX,_dwDegree,_dwRadius
mov @dwX1,eax
invoke _CalcY,_dwDegree,_dwRadius
mov @dwY1,eax
add _dwDegree,180
invoke _CalcX,_dwDegree,10
mov @dwX2,eax
invoke _CalcY,_dwDegree,10
mov @dwY2,eax
invoke MoveToEx,_hDC,@dwX1,@dwY1,NULL
invoke LineTo,_hDC,@dwX2,@dwY2
ret
_DrawLine endp

_CreateClockPic proc
local @stTime:SYSTEMTIME
pushad
[color=FF0000]invoke BitBlt,hDcClock,0,0,CLOCK_SIZE,CLOCK_SIZE,hDcBack,0,0,SRCCOPY[/color]
; 画时钟指针
invoke GetLocalTime,addr @stTime
invoke CreatePen,PS_SOLID,1,0
invoke SelectObject,hDcClock,eax
invoke DeleteObject,eax
movzx eax,@stTime.wSecond
mov ecx,360/60
mul ecx ;秒针度数 = 秒 * 360/60
invoke _DrawLine,hDcClock,eax,60
invoke CreatePen,PS_SOLID,2,0
invoke SelectObject,hDcClock,eax
invoke DeleteObject,eax
movzx eax,@stTime.wMinute
mov ecx,360/60
mul ecx ;分针度数 = 分 * 360/60
invoke _DrawLine,hDcClock,eax,55
invoke CreatePen,PS_SOLID,3,0
invoke SelectObject,hDcClock,eax
invoke DeleteObject,eax
movzx eax,@stTime.wHour
.if eax >= 12
sub eax,12
.endif
mov ecx,360/12
mul ecx
movzx ecx,@stTime.wMinute
shr ecx,1
add eax,ecx
invoke _DrawLine,hDcClock,eax,50
invoke GetStockObject,NULL_PEN
invoke SelectObject,hDcClock,eax
invoke DeleteObject,eax
popad
ret
_CreateClockPic endp

_CreateBackGround proc
local @hDc,@hDcCircle,@hDcMask
local @hBmpBack,@hBmpCircle,@hBmpMask
; 绘制钟面图形
invoke GetDC,hWinMain
mov @hDc,eax
invoke CreateCompatibleDC,@hDc
mov hDcBack,eax
invoke CreateCompatibleDC,@hDc
mov hDcClock,eax
invoke CreateCompatibleDC,@hDc
mov @hDcCircle,eax
invoke CreateCompatibleDC,@hDc
mov @hDcMask,eax
invoke CreateCompatibleBitmap,@hDc,CLOCK_SIZE,CLOCK_SIZE
mov hBmpBack,eax
invoke CreateCompatibleBitmap,@hDc,CLOCK_SIZE,CLOCK_SIZE
mov hBmpClock,eax
invoke ReleaseDC,hWinMain,@hDc
invoke LoadBitmap,hInstance,dwNowBack
mov @hBmpBack,eax
invoke LoadBitmap,hInstance,dwNowCircle
mov @hBmpCircle,eax
mov eax,dwNowCircle
inc eax
invoke LoadBitmap,hInstance,eax
mov @hBmpMask,eax
invoke SelectObject,hDcBack,hBmpBack
invoke SelectObject,hDcClock,hBmpClock
invoke SelectObject,@hDcCircle,@hBmpCircle
invoke SelectObject,@hDcMask,@hBmpMask
invoke CreatePatternBrush,@hBmpBack
push eax
invoke SelectObject,hDcBack,eax
invoke PatBlt,hDcBack,0,0,CLOCK_SIZE,CLOCK_SIZE,PATCOPY
pop eax
invoke DeleteObject,eax
invoke BitBlt,hDcBack,0,0,CLOCK_SIZE,CLOCK_SIZE,@hDcMask,0,0,SRCAND
invoke BitBlt,hDcBack,0,0,CLOCK_SIZE,CLOCK_SIZE,@hDcCircle,0,0,SRCPAINT
invoke DeleteDC,@hDcCircle
invoke DeleteDC,@hDcMask
invoke DeleteObject,@hBmpBack
invoke DeleteObject,@hBmpCircle
invoke DeleteObject,@hBmpMask
ret
_CreateBackGround endp

_DeleteBackGround proc
invoke DeleteDC,hDcBack
invoke DeleteDC,hDcClock
invoke DeleteObject,hBmpBack
invoke DeleteObject,hBmpClock
ret
_DeleteBackGround endp
_Init proc
local @hBmpBack,@hBmpCircle

; 初始化菜单
invoke CreatePopupMenu
mov hMenu,eax
invoke AppendMenu,hMenu,0,IDM_BACK1,offset szMenuBack1
invoke AppendMenu,hMenu,0,IDM_BACK2,offset szMenuBack2
invoke AppendMenu,hMenu,MF_SEPARATOR,0,NULL
invoke AppendMenu,hMenu,0,IDM_CIRCLE1,offset szMenuCircle1
invoke AppendMenu,hMenu,0,IDM_CIRCLE2,offset szMenuCircle2
invoke AppendMenu,hMenu,MF_SEPARATOR,0,NULL
invoke AppendMenu,hMenu,0,IDM_EXIT,offset szMenuExit
invoke CheckMenuRadioItem,hMenu,IDM_BACK1,IDM_BACK2,IDM_BACK1,NULL
invoke CheckMenuRadioItem,hMenu,IDM_CIRCLE1,IDM_CIRCLE2,IDM_CIRCLE1,NULL
; 将窗口设为圆形，并且总在最前
invoke CreateEllipticRgn,0,0,CLOCK_SIZE+1,CLOCK_SIZE+1
push eax
invoke SetWindowRgn,hWinMain,eax,TRUE
pop eax
invoke DeleteObject,eax
invoke SetWindowPos,hWinMain,HWND_TOPMOST,0,0,0,0,\
SWP_NOMOVE or SWP_NOSIZE
; 建立背景
mov dwNowBack,IDB_BACK1
mov dwNowCircle,IDB_CIRCLE1
invoke _CreateBackGround
invoke _CreateClockPic
invoke SetTimer,hWinMain,ID_TIMER,1000,NULL
ret
_Init endp

_Quit proc
invoke KillTimer,hWinMain,ID_TIMER
invoke DestroyWindow,hWinMain
invoke PostQuitMessage,NULL
invoke _DeleteBackGround
invoke DestroyMenu,hMenu
ret
_Quit endp

_ProcWinMain proc uses ebx edi esi hWnd,uMsg,wParam,lParam
local @stPS:PAINTSTRUCT
local @hDC
local @stPos:POINT
mov eax,uMsg
.if eax == WM_TIMER
invoke _CreateClockPic
invoke InvalidateRect,hWnd,NULL,FALSE
.elseif eax == WM_PAINT
invoke BeginPaint,hWnd,addr @stPS
mov @hDC,eax
mov eax,@stPS.rcPaint.right
sub eax,@stPS.rcPaint.left
mov ecx,@stPS.rcPaint.bottom
sub ecx,@stPS.rcPaint.top
invoke BitBlt,@hDC,@stPS.rcPaint.left,@stPS.rcPaint.top,eax,ecx,\
hDcClock,@stPS.rcPaint.left,@stPS.rcPaint.top,SRCCOPY
invoke EndPaint,hWnd,addr @stPS
.elseif eax == WM_CREATE
mov eax,hWnd
mov hWinMain,eax
invoke _Init
.elseif eax == WM_COMMAND
mov eax,wParam
.if ax == IDM_BACK1
mov dwNowBack,IDB_BACK1
invoke CheckMenuRadioItem,hMenu,IDM_BACK1,IDM_BACK2,IDM_BACK1,NULL
.elseif ax == IDM_BACK2
mov dwNowBack,IDB_BACK2
invoke CheckMenuRadioItem,hMenu,IDM_BACK1,IDM_BACK2,IDM_BACK2,NULL
.elseif ax == IDM_CIRCLE1
mov dwNowCircle,IDB_CIRCLE1
invoke CheckMenuRadioItem,hMenu,IDM_CIRCLE1,IDM_CIRCLE2,IDM_CIRCLE1,NULL
.elseif ax == IDM_CIRCLE2
mov dwNowCircle,IDB_CIRCLE2
invoke CheckMenuRadioItem,hMenu,IDM_CIRCLE1,IDM_CIRCLE2,IDM_CIRCLE2,NULL
.elseif ax == IDM_EXIT
call _Quit
xor eax,eax
ret
.endif
invoke _DeleteBackGround
invoke _CreateBackGround
invoke _CreateClockPic
invoke InvalidateRect,hWnd,NULL,FALSE
.elseif eax == WM_CLOSE
call _Quit
; 按下右键时弹出一个菜单
.elseif eax == WM_RBUTTONDOWN
invoke GetCursorPos,addr @stPos
invoke TrackPopupMenu,hMenu,TPM_LEFTALIGN,@stPos.x,@stPos.y,NULL,hWnd,NULL
; 按下左键时移动窗口
.elseif eax == WM_LBUTTONDOWN
invoke SetCursor,hCursorMove
invoke UpdateWindow,hWnd
invoke ReleaseCapture
invoke SendMessage,hWnd,WM_NCLBUTTONDOWN,HTCAPTION,0
invoke SetCursor,hCursorMain
.else
invoke DefWindowProc,hWnd,uMsg,wParam,lParam
ret
.endif
xor eax,eax
ret
_ProcWinMain endp

_WinMain proc
local @stWndClass:WNDCLASSEX
local @stMsg:MSG
invoke GetModuleHandle,NULL
mov hInstance,eax
invoke LoadCursor,hInstance,IDC_MOVE
mov hCursorMove,eax
invoke LoadCursor,hInstance,IDC_MAIN
mov hCursorMain,eax
; 注册窗口类
invoke RtlZeroMemory,addr @stWndClass,sizeof @stWndClass
invoke LoadIcon,hInstance,ICO_MAIN
mov @stWndClass.hIcon,eax
mov @stWndClass.hIconSm,eax
push hCursorMain
pop @stWndClass.hCursor
push hInstance
pop @stWndClass.hInstance
mov @stWndClass.cbSize,sizeof WNDCLASSEX
mov @stWndClass.style,CS_HREDRAW or CS_VREDRAW
mov @stWndClass.lpfnWndProc,offset _ProcWinMain
mov @stWndClass.hbrBackground,COLOR_WINDOW + 1
mov @stWndClass.lpszClassName,offset szClassName
invoke RegisterClassEx,addr @stWndClass
; 建立并显示窗口
invoke CreateWindowEx,NULL,\
offset szClassName,offset szClassName,\
WS_POPUP or WS_SYSMENU,\
100,100,CLOCK_SIZE,CLOCK_SIZE,\
NULL,NULL,hInstance,NULL
mov hWinMain,eax
invoke ShowWindow,hWinMain,SW_SHOWNORMAL
invoke UpdateWindow,hWinMain
; 消息循环
.while TRUE
invoke GetMessage,addr @stMsg,NULL,0,0
.break .if eax == 0
invoke TranslateMessage,addr @stMsg
invoke DispatchMessage,addr @stMsg
.endw
ret
_WinMain endp

; 程序入口，从此处启动
start:
call _WinMain
invoke ExitProcess,NULL
end start