问c++鼠标左键按下帮助

EN

case WM_LBUTTONDOWN:
    iRegularShots=0;
    pt.x = GET_X_LPARAM(lParam); 
    pt.y = GET_Y_LPARAM(lParam); 
    pRegularShots.push_back(pt); 
    InvalidateRect(hWnd, rect, false); 
    break;

VOID fRegularShot(HDC hdc, HWND hWnd) 
{ 
    Graphics graphics(hdc); 
    Image shot(L"RegularShots.png"); 
    long index=0;
    long s=pRegularShots.size();
    while(index < (long)pRegularShots.size()) 
    { 
        graphics.DrawImage(&shot, pRegularShots[index].x, pRegularShots[index].y); 
        ++index;
    } 
} 

switch (message)
    {
    case WM_COMMAND:
        wmId    = LOWORD(wParam);
        wmEvent = HIWORD(wParam);
        // Parse the menu selections:
        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_PAINT:
        hdc = BeginPaint(hWnd, &ps);
        OnPaint(hdc, hWnd, 1);
        if(iRegularShots==0)
        {
            fRegularShot(hdc, hWnd);
        }
        EndPaint(hWnd, &ps);
        break;
    case WM_LBUTTONDOWN:
        iRegularShots=0;
        pt.x = GET_X_LPARAM(lParam); 
        pt.y = GET_Y_LPARAM(lParam); 
        pRegularShots.push_back(pt); 
        InvalidateRect(hWnd, rect, false); 
        return 0;
        break; 
    case WM_LBUTTONUP:
            iRegularShots=1;
            break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}