本课中我们将学习如何在我们的窗口过程函数中处理鼠标按键消息。示例程序演示了如何等待左键按下消息，我们将在按下的位置显示一个字符串。
理论：
和处理键盘输入一样，WINDOWS将捕捉鼠标动作并把它们发送到相关窗口。这些活动包括左、右键按下、移动、双击等(译者注：新式鼠标还包括滚轮消息WM_WHEEL)。WINDOWS并不像处理键盘输入那样把所有的鼠标消息都导向有输入焦点的窗口，任何鼠标经过的窗口都将接收到鼠标消息，无论有否输入焦点。另外，窗口还会接收到鼠标在非客户区移动的消息（WM_NCMOVE），但大多数的情况下我们都会将其忽略掉。 对鼠标的每一个按钮都有两个消息：WM_LBUTTONDOWN,WM_RBUTTONDOWN 。对于三键鼠标还会有WM_MBUTTONDOWN和WM_MBUTTONUP消息，当鼠标在某窗口客户区移动时，该窗口将接收到WM_MOUSEMOVE消息。一个窗口若想处理WM_LBUTTONDBCLK或 WM_RBUTTONDBCLK，那么它的窗口类必须有CS_DBLCLKS风格，否则它就会接受到一堆的按键起落（WM_XBUTTONDOWN或WM_XBUTTONUP)的消息。 对于所有的消息，窗口过程函数传入的参数lParam包含了鼠标的位置，其中底位为x坐标，高位为y坐标，这些坐标值都是相对于窗口客户区的左上角的值，wParam中则包含了鼠标按钮的状态。

例子：
.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

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