画线出现问题，求助
我打算利用鼠标来改变贝塞尔曲线的样子，可是，样子是可以改变，但是原来的却没有消失，很郁闷啊

C/C++ code

// bezier.cpp : 定义应用程序的入口点。//#include "stdafx.h"#include "bezier.h"#define MAX_LOADSTRING 100// 全局变量:HINSTANCE hInst;                                // 当前实例TCHAR szTitle[MAX_LOADSTRING];                    // 标题栏文本TCHAR szWindowClass[MAX_LOADSTRING];            // 主窗口类名// 此代码模块中包含的函数的前向声明:ATOM                MyRegisterClass(HINSTANCE hInstance);BOOL                InitInstance(HINSTANCE, int);LRESULT CALLBACK    WndProc(HWND, UINT, WPARAM, LPARAM);INT_PTR CALLBACK    About(HWND, UINT, WPARAM, LPARAM);int APIENTRY _tWinMain(HINSTANCE hInstance,                     HINSTANCE hPrevInstance,                     LPTSTR    lpCmdLine,                     int       nCmdShow){    UNREFERENCED_PARAMETER(hPrevInstance);    UNREFERENCED_PARAMETER(lpCmdLine);     // TODO: 在此放置代码。    MSG msg;    HACCEL hAccelTable;    // 初始化全局字符串    LoadString(hInstance, IDS_APP_TITLE, szTitle, MAX_LOADSTRING);    LoadString(hInstance, IDC_BEZIER, szWindowClass, MAX_LOADSTRING);    MyRegisterClass(hInstance);    // 执行应用程序初始化:    if (!InitInstance (hInstance, nCmdShow))    {        return FALSE;    }    hAccelTable = LoadAccelerators(hInstance, MAKEINTRESOURCE(IDC_BEZIER));    // 主消息循环:    while (GetMessage(&msg, NULL, 0, 0))    {        if (!TranslateAccelerator(msg.hwnd, hAccelTable, &msg))        {            TranslateMessage(&msg);            DispatchMessage(&msg);        }    }    return (int) msg.wParam;}////  函数: MyRegisterClass()////  目的: 注册窗口类。////  注释:////    仅当希望//    此代码与添加到 Windows 95 中的“RegisterClassEx”//    函数之前的 Win32 系统兼容时，才需要此函数及其用法。调用此函数十分重要，//    这样应用程序就可以获得关联的//    “格式正确的”小图标。//ATOM MyRegisterClass(HINSTANCE hInstance){    WNDCLASSEX wcex;    wcex.cbSize = sizeof(WNDCLASSEX);    wcex.style            = CS_HREDRAW | CS_VREDRAW;    wcex.lpfnWndProc    = WndProc;    wcex.cbClsExtra        = 0;    wcex.cbWndExtra        = 0;    wcex.hInstance        = hInstance;    wcex.hIcon            = LoadIcon(hInstance, MAKEINTRESOURCE(IDI_BEZIER));    wcex.hCursor        = LoadCursor(NULL, IDC_ARROW);    wcex.hbrBackground    = (HBRUSH)(COLOR_WINDOW+1);    wcex.lpszMenuName    = MAKEINTRESOURCE(IDC_BEZIER);    wcex.lpszClassName    = szWindowClass;    wcex.hIconSm        = LoadIcon(wcex.hInstance, MAKEINTRESOURCE(IDI_SMALL));    return RegisterClassEx(&wcex);}////   函数: InitInstance(HINSTANCE, int)////   目的: 保存实例句柄并创建主窗口////   注释:////        在此函数中，我们在全局变量中保存实例句柄并//        创建和显示主程序窗口。//BOOL InitInstance(HINSTANCE hInstance, int nCmdShow){   HWND hWnd;   hInst = hInstance; // 将实例句柄存储在全局变量中   hWnd = CreateWindow(szWindowClass, szTitle, WS_OVERLAPPEDWINDOW,      CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, NULL, NULL, hInstance, NULL);   if (!hWnd)   {      return FALSE;   }   ShowWindow(hWnd, nCmdShow);   UpdateWindow(hWnd);   return TRUE;}//Draw the bezier void DrawBezier(HDC hdc,POINT apt[]){    PolyBezier(hdc,apt,4);    MoveToEx(hdc,apt[0].x,apt[0].y,NULL);    LineTo(hdc,apt[1].x,apt[1].y);    MoveToEx(hdc,apt[2].x,apt[2].y,NULL);    LineTo(hdc,apt[3].x,apt[3].y);}////  函数: WndProc(HWND, UINT, WPARAM, LPARAM)////  目的: 处理主窗口的消息。////  WM_COMMAND    - 处理应用程序菜单//  WM_PAINT    - 绘制主窗口//  WM_DESTROY    - 发送退出消息并返回////LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam){    HPEN hpen;    int wmId, wmEvent;    PAINTSTRUCT ps;    HDC hdc;    int cxClient,cyClient;    static POINT apt[4];    switch (message)    {    case WM_COMMAND:        wmId    = LOWORD(wParam);        wmEvent = HIWORD(wParam);        // 分析菜单选择:        switch (wmId)        {        case IDM_ABOUT:            DialogBox(hInst, MAKEINTRESOURCE(IDD_ABOUTBOX), hWnd, About);            break;        case IDM_EXIT:            DestroyWindow(hWnd);            break;        default:            return DefWindowProc(hWnd, message, wParam, lParam);        }        break;    case WM_SIZE:        cxClient=LOWORD(lParam);        cyClient=HIWORD(lParam);        apt[0].x=cxClient/4;        apt[0].y=cyClient/2;        apt[1].x=cxClient/2;        apt[1].y=cyClient/4;        apt[2].x=cxClient/2;        apt[2].y=3*cyClient/4;        apt[3].x=3*cxClient/4;        apt[3].y=cyClient/2;        break;    case WM_LBUTTONDOWN:    case WM_RBUTTONDOWN:    case WM_MOUSEMOVE:        hpen=CreatePen(PS_SOLID,2,RGB(255,0,0));        if (wParam&MK_LBUTTON||wParam&MK_RBUTTON)        {            hdc=GetDC(hWnd);            SelectObject(hdc,hpen);            DrawBezier(hdc,apt);            if (wParam&MK_LBUTTON)            {                apt[1].x=LOWORD(lParam);                apt[1].y=HIWORD(lParam);            }            if (wParam&MK_RBUTTON)            {                apt[2].x=LOWORD(lParam);                apt[2].y=HIWORD(lParam);            }            SelectObject(hdc,GetStockObject(WHITE_PEN));            DrawBezier(hdc,apt);            ReleaseDC(hWnd,hdc);        }        DeleteObject(hpen);        hdc=GetDC(hWnd);        SelectObject(hdc,GetStockObject(BLACK_PEN));        ReleaseDC(hWnd,hdc);        break;    case WM_PAINT:        InvalidateRect(hWnd,NULL,FALSE);        hdc = BeginPaint(hWnd, &ps);        // TODO: 在此添加任意绘图代码...                DrawBezier(hdc,apt);        EndPaint(hWnd, &ps);        break;    case WM_DESTROY:        PostQuitMessage(0);        break;    default:        return DefWindowProc(hWnd, message, wParam, lParam);    }    return 0;}// “关于”框的消息处理程序。INT_PTR CALLBACK About(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam){    UNREFERENCED_PARAMETER(lParam);    switch (message)    {    case WM_INITDIALOG:        return (INT_PTR)TRUE;    case WM_COMMAND:        if (LOWORD(wParam) == IDOK || LOWORD(wParam) == IDCANCEL)        {            EndDialog(hDlg, LOWORD(wParam));            return (INT_PTR)TRUE;        }        break;    }    return (INT_PTR)FALSE;} 
 

[解决办法]
画新的前用Invalidate刷一下
[解决办法]
刷新背景会闪的。
用异或方式画线，画新线的时候先将旧线再画一遍，两次异或旧线就不见了。然后画新线。