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
// 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;}