win32 api 初级问题

最近我在学习《windows程序设计 第五版》这本书，有很多不懂的地方，下面就是其中一个，希望大侠帮忙修改源程序

下面的程序是“对话框”-“模态对话框”-“定义自己的控件”里的一个例子，我想根据书上的要求添加一个功能：
我在对话框里自定义了一个按钮（.rc文件表述如下），问题是如何实现书上的描述：
“按钮不会像普通的按键那样闪烁。要翻转按键内的颜色，窗口消息处理程序必须处理WM_KEYDOWN（来自空格键）和WM_LBUTTONDOWN消息。窗口消息处理程序还必须在收到WM_LBUTTONDOWN消息时拦截鼠标，并且，如果当按钮还处于按下状态，而鼠标移到了子窗口的显示区域之外，那么得要释放鼠标拦截（并将按钮的内部颜色回复为正常状态）。只有在鼠标被拦截时松开该按钮，子窗口才会给其父窗口送回一个WM_COMMAND消息。”
#include "resource.h"
#include "afxres.h"
/////////////////////////////////////////////////////////////////////////////
// Dialog
ABOUTBOX DIALOG DISCARDABLE 32, 32, 180, 100
STYLE DS_MODALFRAME | WS_POPUP
FONT 8, "MS Sans Serif"
BEGIN
CONTROL "OK",IDOK,"EllipPush",WS_GROUP | WS_TABSTOP,73,79,32,14
ICON "ABOUT3",IDC_STATIC,7,7,20,20
CTEXT "About3",IDC_STATIC,40,12,100,8
CTEXT "About Box Demo Program",IDC_STATIC,7,40,166,8
CTEXT "(c) Charles Petzold, 1998",IDC_STATIC,7,52,166,8
END
/////////////////////////////////////////////////////////////////////////////
// Menu
ABOUT3 MENU DISCARDABLE
BEGIN
POPUP "&Help"
BEGIN
MENUITEM "&About About3...", IDM_APP_ABOUT
END
END
/////////////////////////////////////////////////////////////////////////////
// Icon
ABOUT3 ICON DISCARDABLE "icon1.ico"

.c文件程序如下

#include <windows.h>

#include "resource.h"



LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

BOOL    CALLBACK AboutDlgProc (HWND, UINT, WPARAM, LPARAM) ;

LRESULT CALLBACK EllipPushWndProc (HWND, UINT, WPARAM, LPARAM) ;



int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,

                    PSTR szCmdLine, int iCmdShow)

{

     static TCHAR szAppName[] = TEXT ("About3") ;

     MSG          msg ;

     HWND         hwnd ;

     WNDCLASS     wndclass ;



     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;

     wndclass.lpfnWndProc   = WndProc ;

     wndclass.cbClsExtra    = 0 ;

     wndclass.cbWndExtra    = 0 ;

     wndclass.hInstance     = hInstance ;

     wndclass.hIcon         = LoadIcon (hInstance, szAppName) ;

     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;

     wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;

     wndclass.lpszMenuName  = szAppName ;

     wndclass.lpszClassName = szAppName ;

     

     if (!RegisterClass (&wndclass))

     {

          MessageBox (NULL, TEXT ("This program requires Windows NT!"),

                      szAppName, MB_ICONERROR) ;

          return 0 ;

     }

     

     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;

     wndclass.lpfnWndProc   = EllipPushWndProc ;

     wndclass.cbClsExtra    = 0 ;

     wndclass.cbWndExtra    = 0 ;

     wndclass.hInstance     = hInstance ;

     wndclass.hIcon         = NULL ;

     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;

     wndclass.hbrBackground = (HBRUSH) (COLOR_BTNFACE + 1) ;

     wndclass.lpszMenuName  = NULL ;

     wndclass.lpszClassName = TEXT ("EllipPush") ;

	 

     RegisterClass (&wndclass) ;

     

     hwnd = CreateWindow (szAppName, TEXT ("About Box Demo Program"),

                          WS_OVERLAPPEDWINDOW,

                          CW_USEDEFAULT, CW_USEDEFAULT,

                          CW_USEDEFAULT, CW_USEDEFAULT,

                          NULL, NULL, hInstance, NULL) ;

     

     ShowWindow (hwnd, iCmdShow) ;

     UpdateWindow (hwnd) ; 

     

     while (GetMessage (&msg, NULL, 0, 0))

     {

          TranslateMessage (&msg) ;

          DispatchMessage (&msg) ;

     }

     return msg.wParam ;

}



LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)

{

	static HINSTANCE hInstance ;

	

     switch (message)

     {

     case WM_CREATE :

          hInstance = ((LPCREATESTRUCT) lParam)->hInstance ;

          return 0 ;

          

     case WM_COMMAND :

          switch (LOWORD (wParam))

          {

          case IDM_APP_ABOUT :

               DialogBox (hInstance, TEXT ("AboutBox"), hwnd, AboutDlgProc) ;

               return 0 ;

          }

          break ;

          

     case WM_DESTROY :

          PostQuitMessage (0) ;

          return 0 ;

     }

     return DefWindowProc (hwnd, message, wParam, lParam) ;

}



BOOL CALLBACK AboutDlgProc (HWND hDlg, UINT message, 

                            WPARAM wParam, LPARAM lParam)

{

     switch (message)

     {

     case WM_INITDIALOG :

          return TRUE ;

          

     case WM_COMMAND :

          switch (LOWORD (wParam))

          {

          case IDOK :

               EndDialog (hDlg, 0) ;

               return TRUE ;

          }

          break ;

     }

     return FALSE ;

}



LRESULT CALLBACK EllipPushWndProc (HWND hwnd, UINT message, 

                                   WPARAM wParam, LPARAM lParam)

{

     TCHAR       szText[40] ;

     HBRUSH      hBrush ;

     HDC         hdc ;

     PAINTSTRUCT ps ;

     RECT        rect ;

     

     switch (message)

     {

     case WM_PAINT :

          GetClientRect (hwnd, &rect) ;

          GetWindowText (hwnd, szText, sizeof (szText)) ;

          

          hdc = BeginPaint (hwnd, &ps) ;

          

          hBrush = CreateSolidBrush (GetSysColor (COLOR_WINDOW)) ;

          hBrush = (HBRUSH) SelectObject (hdc, hBrush) ;

          SetBkColor (hdc, GetSysColor (COLOR_WINDOW)) ;

          SetTextColor (hdc, GetSysColor (COLOR_WINDOWTEXT)) ;

          

          Ellipse (hdc, rect.left, rect.top, rect.right, rect.bottom) ;

          DrawText (hdc, szText, -1, &rect,

                    DT_SINGLELINE | DT_CENTER | DT_VCENTER) ;

          

          DeleteObject (SelectObject (hdc, hBrush)) ;

          

          EndPaint (hwnd, &ps) ;

          return 0 ;

     

	 case WM_LBUTTONDOWN:



     case WM_KEYUP :

          if (wParam != VK_SPACE)

               break ;

                                             // fall through

     case WM_LBUTTONUP :

          SendMessage (GetParent (hwnd), WM_COMMAND,

               GetWindowLong (hwnd, GWL_ID), (LPARAM) hwnd) ;

          return 0 ;

     }

     return DefWindowProc (hwnd, message, wParam, lParam) ;

}