.386
.MODEL FLAT,STDCALL
option casemap:none WinMain proto :DWORD,:DWORD,:DWORD,:DWORD
INCLUDE \MASM32\INCLUDE\WINDOWS.INC
INCLUDE \MASM32\INCLUDE\USER32.INC
INCLUDE \MASM32\INCLUDE\KERNEL32.INC
INCLUDE \MASM32\INCLUDE\GDI32.INC
INCLUDELIB \MASM32\LIB\USER32.LIB
INCLUDELIB \MASM32\LIB\KERNEL32.LIB
INCLUDELIB \MASM32\LIB\GDI32.LIB
.DATA
CLASSNAME DB "SIMPLEWINCLASS",0
APPNAME DB "OUR FIRST WINDOW",0
MOUSECLICK DB 0 ; 0=no click yet
.DATA?
hInstance HINSTANCE ?
CommandLine LPSTR ?
hitpoint POINT <>
.CODE
START:
INVOKE GETMODULEHANDLE, NULL
MOV HINSTANCE,EAX
INVOKE GETCOMMANDLINE
MOV COMMANDLINE,EAX
INVOKE WINMAIN, HINSTANCE,NULL,COMMANDLINE, SW_SHOWDEFAULT
INVOKE EXITPROCESS,EAX
WINMAIN PROC HINST:HINSTANCE,HPREVINST:HINSTANCE,CMDLINE:LPSTR,CMDSHOW:DWORD
LOCAL WC:WNDCLASSEX
LOCAL MSG:MSG
LOCAL HWND:HWND
MOV WC.CBSIZE,SIZEOF WNDCLASSEX
MOV WC.STYLE, CS_HREDRAW OR CS_VREDRAW
MOV WC.LPFNWNDPROC, OFFSET WNDPROC
MOV WC.CBCLSEXTRA,NULL
MOV WC.CBWNDEXTRA,NULL
PUSH HINST
POP WC.HINSTANCE
MOV WC.HBRBACKGROUND,COLOR_WINDOW+1
MOV WC.LPSZMENUNAME,NULL
MOV WC.LPSZCLASSNAME,OFFSET CLASSNAME
INVOKE LOADICON,NULL,IDI_APPLICATION
MOV WC.HICON,EAX
MOV WC.HICONSM,EAX
INVOKE LOADCURSOR,NULL,IDC_ARROW
MOV WC.HCURSOR,EAX
INVOKE REGISTERCLASSEX, ADDR WC
INVOKE CREATEWINDOWEX,NULL,ADDR CLASSNAME,ADDR APPNAME,\
WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,\
CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,NULL,NULL,\
hInst,NULL
MOV HWND,EAX
INVOKE SHOWWINDOW, HWND,SW_SHOWNORMAL
INVOKE UPDATEWINDOW, HWND
.WHILE TRUE
INVOKE GETMESSAGE, ADDR MSG,NULL,0,0
.BREAK .IF (!EAX)
INVOKE DISPATCHMESSAGE, ADDR MSG
.ENDW
MOV EAX,MSG.WPARAM
RET
WINMAIN ENDP
WNDPROC PROC HWND:HWND, UMSG:UINT, WPARAM:WPARAM, LPARAM:LPARAM
LOCAL HDC:HDC
LOCAL PS:PAINTSTRUCT
.IF UMSG==WM_DESTROY
INVOKE POSTQUITMESSAGE,NULL
.ELSEIF UMSG==WM_LBUTTONDOWN
MOV EAX,LPARAM
AND EAX,0FFFFH
MOV HITPOINT.X,EAX
MOV EAX,LPARAM
SHR EAX,16
MOV HITPOINT.Y,EAX
MOV MOUSECLICK,TRUE
INVOKE INVALIDATERECT,HWND,NULL,TRUE
.ELSEIF UMSG==WM_PAINT
INVOKE BEGINPAINT,HWND, ADDR PS
MOV HDC,EAX
.IF MOUSECLICK
INVOKE LSTRLEN,ADDR APPNAME
INVOKE TEXTOUT,HDC,HITPOINT.X,HITPOINT.Y,ADDR APPNAME,EAX
.ENDIF
INVOKE ENDPAINT,HWND, ADDR PS
.ELSE
INVOKE DEFWINDOWPROC,HWND,UMSG,WPARAM,LPARAM
RET
.ENDIF
XOR EAX,EAX
RET
WNDPROC ENDP
END START
.ELSEIF UMSG==WM_LBUTTONDOWN
MOV EAX,LPARAM
AND EAX,0FFFFH
MOV HITPOINT.X,EAX
MOV EAX,LPARAM
SHR EAX,16
MOV HITPOINT.Y,EAX
MOV MOUSECLICK,TRUE
INVOKE INVALIDATERECT,HWND,NULL,TRUE
窗口过程处理了WM_LBUTTONDOWN消息，当接收到该消息时，lParam中包含了相对于窗口客户区左上角的坐标，我们把它保存下来，放到一个结构体变量（POINT）中，该结构体变量的定义如下：
然后我们把标志量MouseClick设为TRUE，这表明至少有一次在客户区的左键按下消息。
MOV EAX,LPARAM
AND EAX,0FFFFH
MOV HITPOINT.X,EAX
由于lParam是一个32位长的数，其中高、底16位分别包括了x、y坐标所以我们做一些小处理，以便保存它们。
SHR EAX,16
MOV HITPOINT.Y,EAX
保存完坐标后我们设标志MouseClick为TRUE，这是在处理WM_PAINT时用来判断是否有鼠标左键按下消息。然后我们调用InvalidateRect（）函数迫使WINDOWS重新绘制客户区。
.IF MouseClick
绘制客户区的代码首先检测MouseClick标志位，再决定是否重绘。因为我们在首次显示窗口时还没有左键按下的消息，所以我们在初始时把该标志设为FALSE，告诉WINDOWS不要重绘客户区，当有左键按下的消息时，它会在鼠标按下的位置绘制字符串。注意在调用TextOut（）函数时，其关于字符串长度的参数是调用lstrlen（）函数来计算的。
INVOKE LSTRLEN,ADDR APPNAME
INVOKE TEXTOUT,HDC,HITPOINT.X,HITPOINT.Y,ADDR APPNAME,EAX
.ENDIF