/// <summary>
/// 窗体句柄附加数据长度
/// </summary>
#define CTRLWINDOWEXTRA 32


/// <summary>
/// 声明回调函数的宏
/// </summary>
#define DECLARE_WNDPROC(ProcName)		LRESULT CALLBACK ProcName(HWND, UINT, WPARAM, LPARAM);


/// <summary>
/// 声明钟表组件的消息回调函数
/// </summary>
DECLARE_WNDPROC(ClockCtrlProc)


/// <summary>
/// 注册窗体类
/// </summary>
static
ATOM _RegistCtrlClass(HINSTANCE hInst, LPCTSTR lpszClsName, WNDPROC pWndProc)
{
	WNDCLASSEX wcex = {
		sizeof(WNDCLASSEX),
		CS_VREDRAW | CS_HREDRAW | CS_DBLCLKS,
		pWndProc,
		0, CTRLWINDOWEXTRA, hInst, NULL, NULL,
		(HBRUSH)(COLOR_BTNFACE + 1),
		0, lpszClsName, NULL
	};
	return RegisterClassEx(&wcex);
}


/// <summary>
/// 初始化用户自定义控件
/// </summary>
BOOL InitializeUserControls()
{
	ATOM atom = _RegistCtrlClass(_INSTANCE, _T("ClockCtrl"), (WNDPROC)ClockCtrlProc);
	_ASSERT(atom);
	if (atom == 0)
		return FALSE;
	return TRUE;
}

/// <summary>
/// 保存绘图对象的结构体
/// </summary>
typedef struct tagCLK_GDIOBJ
{
	HBRUSH brushBackground,		// 控件背景画刷
		brushDigitalDark,		// 数字表盘暗色画刷
		brushDigitalLight,		// 数字表盘亮色画刷
		brushClockBackground;	// 表盘背景
	LOGFONT fontDate,		// 控件全局字体
		fontClockNumber;	// 表盘数字字体
	HPEN penBorder,			// 控件边框画笔
		penDigitalBorder,	// 数字边框画笔
		penClockBorder,		// 表盘边框画笔
		penClockArrow;		// 表盘箭头画笔
} CLK_GDIOBJ, *LPCLK_GDIOBJ;


/// <summary>
/// 保存运行时信息的结构体
/// </summary>
typedef struct tagCLK_RUNTIME
{
	SYSTEMTIME stimNow;	// 当前时间
	BOOL isDigitalSecondDark;	// 数字表盘的秒针是否为灰色
	UINT_PTR timSecond;	// 按秒进行的定时器句柄
} CLK_RUNTIME, *LPCLK_RUNTIME;


/// <summary>
/// 表示数据位置的常量
/// </summary>
#define CLKP_GDIOBJ	0	// 0~3字节存放CLK_GDIOBJ结构体变量地址
#define CLKP_RUNTIME	(CLKP_GDIOBJ + sizeof(LPCLK_GDIOBJ))	// 4~7字节存放CLK_RUNTIME结构体变量地址

/// <summary>
/// 窗口创建消息
/// </summary>
static
int _OnCreate(HWND hCtrl, LPCREATESTRUCT lpcs)
{
	LPCLK_GDIOBJ pGdi;
	LPCLK_RUNTIME pRunTm;
	HFONT fontDef;

	if (!_LOCHEAP)
		_LOCHEAP = HeapCreate(0, 0, 0);		// 创建本地堆句柄

	fontDef = (HFONT)GetStockObject(DEFAULT_GUI_FONT);

	/// 设置默认的GDI对象
	pGdi = HeapAlloc(_LOCHEAP, HEAP_ZERO_MEMORY, sizeof(CLK_GDIOBJ));
	GetObject(fontDef, sizeof(LOGFONT), &pGdi->fontDate);
	GetObject(fontDef, sizeof(LOGFONT), &pGdi->fontClockNumber);
	pGdi->brushBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
	pGdi->brushClockBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
	pGdi->brushDigitalDark = CreateSolidBrush(RGB(0xEE, 0xEE, 0xEE));
	pGdi->brushDigitalLight = CreateSolidBrush(RGB(0xFF, 0, 0));
	pGdi->penBorder = CreatePen(PS_SOLID, 1, RGB(0x90, 0xC4, 0xE8));
	pGdi->penClockArrow = (HPEN)GetStockObject(BLACK_PEN);
	pGdi->penClockBorder = (HPEN)GetStockObject(BLACK_PEN);
	pGdi->penDigitalBorder = (HPEN)GetStockObject(WHITE_PEN);
	SetWindowLongPtr(hCtrl, CLKP_GDIOBJ, (LONG_PTR)pGdi);	// 存储GDI对象结构体指针

	/// 设置默认的运行时状态
	pRunTm = HeapAlloc(_LOCHEAP, HEAP_ZERO_MEMORY, sizeof(CLK_RUNTIME));
	pRunTm->isDigitalSecondDark = FALSE;
	GetLocalTime(&pRunTm->stimNow);
	SetWindowLongPtr(hCtrl, CLKP_RUNTIME, (LONG_PTR)pRunTm);	// 存储运行时状态结构体指针

	SendMessage(hCtrl, WM_START, 0, 0);	// 发送启动消息
	return 0;
}

/// <summary>
/// 窗口销毁消息
/// </summary>
static
void _OnDestory(HWND hCtrl)
{
	LPCLK_GDIOBJ pGdi;
	LPCLK_RUNTIME pRunTm;

	pGdi = (LPCLK_GDIOBJ)GetWindowLongPtr(hCtrl, CLKP_GDIOBJ);	// 获取GDI对象结构体
	if (pGdi)
	{
		/// 删除所有的GDI对象
		DeleteObject(pGdi->brushBackground);
		DeleteObject(pGdi->brushClockBackground);
		DeleteObject(pGdi->brushDigitalDark);
		DeleteObject(pGdi->brushDigitalLight);
		DeleteObject(pGdi->penBorder);
		DeleteObject(pGdi->penClockArrow);
		DeleteObject(pGdi->penClockBorder);

		HeapFree(_LOCHEAP, 0, pGdi);	// 从内存中删除结构体
	}

	pRunTm = (LPCLK_RUNTIME)GetWindowLongPtr(hCtrl, CLKP_RUNTIME);	// 获取运行时状态结构体
	if (pRunTm)
	{
		KillTimer(hCtrl, pRunTm->timSecond);	// 停止定时器
		HeapFree(_LOCHEAP, 0, pRunTm);	// 从内存中删除结构体
	}
}

一些说明