在Windows系统中提供了一种系统消息挂钩的(Message hook)功能，使用消息挂钩，可以实时监视处理系统中的各种消息。很多鼠标增强软件就是利用消息挂钩来拦截所有的鼠标消息进行处理的。
要设置鼠标消息挂钩，一般先建立一个使用鼠标消息挂钩的动态连接库(DLL)文件，然后就可以在其它程序中使用这个DLL文件处理鼠标消息。
下面的程序介绍通过鼠标消息挂钩监视鼠标消息，从而实现类似于一些鼠标增强软件一样的使窗口上下左右滚动的功能。

1．建立动态连接库
选择菜单 File|New ，选择DLL产生一个DLL模版，保存为 MHook.Dpr
//MHook.Dpr源程序
library MHook;

uses
SysUtils,
Classes,
hkproc in ''hkproc.pas'';

exports
EnableMouseHook,
DisableMouseHook;

begin
hNextHookProc:=0;
procSaveExit:=ExitProc;
ExitProc:=@HotKeyHookExit;
end.

再选择菜单 File|New ，选择Unit建立一个Pas文件，保存为 HKProc.pas
//HKProc.pas源程序
unit hkproc;

interface
uses
Windows,Messages;
const
Move_Up = 0;

Move_Down=1;
Move_Left=2;
Move_Right=3;
var
hNextHookProc:HHook;
procSaveExit:Pointer;
M_Direct:Integer;
LPoint:TPoint;
NowWindow:Integer;

function MouseProc(iCode:Integer;wParam:WPARAM;
lParam:Pointer):LRESULT; stdcall;export;
function EnableMouseHook(WndHandle:integer):BOOL;export;

function DisableMouseHook:BOOL;export;
function GetDirect(FPoint : TPoint;LPoint : TPoint):integer;
procedure HotKeyHookExit;far;

　

implementation

//GetDirect函数根据光标的移动决定窗口滚动的方向。
function GetDirect(FPoint : TPoint;LPoint : TPoint):integer;
var
iWidth,iHeight:integer;
begin
iWidth:=LPoint.x-FPoint.x;
iHeight:=lPoint.y-FPoint.y;
Result:=-1;

if ((iWidth=0)or(iHeight=0))then
exit;

if ((abs(iWidth) div abs(iHeight))>=2) then
if iWidth<0 then //Move to left
Result:=Move_Left
else
Result:=Move_Right

else if ((abs(iHeight) div abs(iWidth))>=2) then
if iHeight<0 then //Move to top
Result:=Move_Up
else
Result:=Move_Down;

end;

function MouseProc(iCode:Integer;wParam:WPARAM;
lParam:Pointer):LRESULT; stdcall;export;
var
pMouse:^MOUSEHOOKSTRUCT;
l:integer;
begin
//如果用户按下鼠标右键同时Scroll Lock键为按下状态则
//滚动窗口。
if ((wParam=WM_RBUTTONDOWN) and Boolean(GetKeyState(145))) then
begin
pMouse:=lParam;
l:=GetDirect(lPoint,pMouse.pt);
if l>=0 then
M_Direct:=l;
lPoint:=pMouse.pt;

NowWindow:=WindowFromPoint(lPoint);
if M_Direct=Move_Up then
SendMessage(NowWindow,WM_VSCROLL,SB_PAGEUP,0)
else if M_Direct=Move_Down then

SendMessage(NowWindow,WM_VSCROLL,SB_PAGEDOWN,0)
else if M_Direct=Move_Left then
SendMessage(NowWindow,WM_HSCROLL,SB_PAGELEFT,0)
else if M_Direct=Move_Right then
SendMessage(NowWindow,WM_HSCROLL,SB_PAGERIGHT,0);
Result:=1;
exit;
end
else if ((wParam=WM_RBUTTONUP) and Boolean(GetKeyState(145))) then
Result:=1
else
begin
Result:=0;
if iCode<0 then
begin
Result:=CallNextHookEx(hNextHookProc,iCode,wParam,
integer(lParam));
Exit;
end;
end;
end;

function EnableMouseHook(WndHandle:integer):BOOL;export;
begin
GetCursorPos(lPoint);
Result:=False;
if hNextHookProc<>0 then
exit;
//设置Mouse hook
hNextHookProc:=SetWindowsHookEx(WH_MOUSE,@MouseProc,
Hinstance,0);
Result:=hNextHookPro