program Project1;uses  Windows,  Messages;{供 WM_LBUTTONDOWN 消息调用的自定义过程}procedure OnLButtonDown(h: HWND);var  BrushHandle: HBRUSH;  Rect: TRect;begin  GetClientRect(h, Rect);                        {获取客户区矩形}  BrushHandle := CreateSolidBrush(RGB(255,0,0)); {建立红色笔刷}  FillRect(GetDC(h), Rect, BrushHandle);         {填充客户区}  DeleteObject(BrushHandle);                     {删除笔刷}end;{供 WM_LBUTTONUP 消息调用的自定义过程}procedure OnLButtonUp(h: HWND);var  Rect: TRect;begin  GetClientRect(h, Rect);         {获取客户区矩形}  InvalidateRect(h, @Rect, True); {使客户区无效, 从而强制重绘}end;{供 WM_MOUSEMOVE 消息调用的自定义过程}procedure OnMouseMove(h: HWND; lParam: Integer);var  pt: TPoint;  buf: array[0..255] of Char;begin  pt.X := LoWord(lParam); {lParam 中的低两位是 x 坐标}  pt.Y := HiWord(lParam); {lParam 中的高两位是 y 坐标}  wvsprintf(buf, '%d, %d', @pt); {格式化到缓冲区}  SetWindowText(h, buf);         {显示在标题}end;function WndProc(wnd: HWND; msg: UINT; wParam: Integer; lParam: Integer): Integer; stdcall;begin  Result := 0;  case msg of    WM_LBUTTONDOWN: OnLButtonDown(wnd); {鼠标左键按下的消息}    WM_LBUTTONUP  : OnLButtonUp(wnd);   {鼠标左键抬起的消息}    WM_MOUSEMOVE  : OnMouseMove(wnd, lParam);   {鼠标移动的消息, 坐标位置在 lParam 中}    WM_DESTROY    : PostQuitMessage(0);  else    Result := DefWindowProc(wnd, msg, wParam, lParam);  end;end;function RegMyWndClass: Boolean;var  cls: TWndClass;begin  cls.style         := CS_HREDRAW or CS_VREDRAW;  cls.lpfnWndProc   := @WndProc;  cls.cbClsExtra    := 0;  cls.cbWndExtra    := 0;  cls.hInstance     := HInstance;  cls.hIcon         := 0;  cls.hCursor       := LoadCursor(0, IDC_ARROW);  cls.hbrBackground := HBRUSH(COLOR_WINDOW + 1);  cls.lpszMenuName  := nil;  cls.lpszClassName := 'MyWnd';  Result := RegisterClass(cls) <> 0;end;{程序入口}const  tit = 'New Form';  ws = WS_OVERLAPPEDWINDOW;  x = 100; y = 100; w = 300; h = 180;var  hWnd: THandle;  Msg : TMsg;begin  RegMyWndClass;  hWnd := CreateWindow('MyWnd', tit, ws, x, y, w, h, 0, 0, HInstance, nil);  ShowWindow(hWnd, SW_SHOWNORMAL);  UpdateWindow(hWnd);  while(GetMessage(Msg, 0, 0, 0)) do  begin    TranslateMessage(Msg);    DispatchMessage(Msg);  end;end.