Listview custom drawing grid lines. Scrolling problem.

#include <Windows.h>
#include <string>
#include <commctrl.h>

#pragma comment (lib,"Comctl32.lib")
#pragma comment (lib,"uxtheme.lib")

HWND g_hWndListView;

static HINSTANCE hInst;

LRESULT CALLBACK MainProc(HWND hWnd, UINT msg, WPARAM wp, LPARAM lp);

void InitListview(HWND hListview) {

    ListView_SetExtendedListViewStyle(hListview, LVS_EX_FULLROWSELECT
     | LVS_EX_DOUBLEBUFFER | LVS_EX_HEADERDRAGDROP);
    ListView_SetBkColor(hListview, RGB(32, 32, 32));
    ListView_SetTextBkColor(hListview, RGB(32, 32, 32));
    ListView_SetTextColor(hListview, RGB(240, 240, 240));

    // Hide focus dots
    SendMessage(hListview, WM_CHANGEUISTATE, 
                MAKELONG(UIS_SET, UISF_HIDEFOCUS), 0);

    static HWND hwndHeader = (HWND)SendMessageW
                             (hListview, LVM_GETHEADER, 0, 0);

    LVCOLUMN lvColumn;
    lvColumn.mask = LVCF_TEXT | LVCF_WIDTH;
    lvColumn.cx = 200;
    
    lvColumn.pszText = (LPWSTR)L"Header 1";
    SendMessage(hListview, LVM_INSERTCOLUMN, 0, (LPARAM)&lvColumn);

    lvColumn.pszText = (LPWSTR)L"Header 2";
    SendMessage(hListview, LVM_INSERTCOLUMN, 1, (LPARAM)&lvColumn);

    lvColumn.pszText = (LPWSTR)L"Header 3";
    SendMessage(hListview, LVM_INSERTCOLUMN, 2, (LPARAM)&lvColumn);

    LVITEM lvItem;
    lvItem.mask = LVIF_STATE | LVIF_TEXT;
    lvItem.state = LVIF_PARAM;
    lvItem.stateMask = NULL;

    for (int i = 0; i < 20; i++) {

        lvItem.iSubItem = 0;
        lvItem.iItem = i;
        lvItem.pszText = (LPWSTR)L"Item";
        SendMessage(hListview, LVM_INSERTITEM, 0, (LPARAM)&lvItem);
    }
}
void CreateListview(HWND hWnd) {


    HWND hListview = CreateWindowEx(WS_EX_CLIENTEDGE, WC_LISTVIEW, 
                     L"", WS_TABSTOP | WS_CHILD | WS_VISIBLE | 
                     LVS_REPORT, 0, 0, 655, 160, hWnd, NULL, NULL, NULL);

    ::g_hWndListView = hListview;

    InitListview(hListview);
}

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPr, 
                   LPSTR args, int ncmdshow) {

    WNDCLASS WindowClass = { 0 };
    WindowClass.hbrBackground = CreateSolidBrush(0);
    WindowClass.hCursor = LoadCursor(NULL, IDC_ARROW);
    WindowClass.hInstance = hInst;
    //WindowClass.hIcon = LoadIcon(hInst, 0);
    WindowClass.lpszClassName = L"MainWindClass";
    WindowClass.lpfnWndProc = MainProc;  

    if (!RegisterClassW(&WindowClass)) {

        return -1;
    }

    int wCntr = GetSystemMetrics(SM_CXSCREEN) / 2;
    int hCntr = GetSystemMetrics(SM_CYSCREEN) / 2;

    HWND MainWindow = CreateWindowA("MainWindClass", "Main", 
    WS_OVERLAPPEDWINDOW | WS_VISIBLE, wCntr - (655 / 2), 
    hCntr - (200 / 2), 800, 400, NULL, NULL, NULL, NULL);

    MSG MainMsg = { 0 };
    while (GetMessage(&MainMsg, NULL, NULL, NULL)) {

        TranslateMessage(&MainMsg);
        DispatchMessage(&MainMsg);
    }

    return 0;
}

void ListView_DrawGridLines(HDC hDC,COLORREF GridColor)
{
    HWND hwndHeader;
    DWORD Counter = 0;
    DWORD ColumnsCount;
    DWORD ColumnWidth;
    RECT rectHeader;
    RECT rectLV;
    RECT ItemRect = { 0 };
    DWORD ItemHeight;
    int scrollHPos;
    COLORREF oldBkColor;
    RECT LineRect{ 0 };
    DWORD borderWidth;
    DWORD LineIndex;

    oldBkColor = SetBkColor(hDC, GridColor);
    hwndHeader = (HWND)SendMessage(g_hWndListView, LVM_GETHEADER, 0, 0);
    ColumnsCount = SendMessage(hwndHeader, HDM_GETITEMCOUNT, 0, 0);

    GetClientRect(g_hWndListView, &rectLV);
    GetClientRect(hwndHeader, &rectHeader);
    
    //Vertical lines
    scrollHPos = GetScrollPos(g_hWndListView, SB_HORZ) * -1;
    if (scrollHPos >= rectLV.right)
        return;
    
    borderWidth = GetSystemMetrics(SM_CXBORDER);

    while (Counter < ColumnsCount)
    {
        ColumnWidth = SendMessage(g_hWndListView, 
                                  LVM_GETCOLUMNWIDTH, Counter, 0);
        scrollHPos = scrollHPos + ColumnWidth;
        if (scrollHPos <= 0)
            break;

        LineRect.left = scrollHPos;
        LineRect.top = rectHeader.bottom;
        LineRect.right = scrollHPos + borderWidth;
        LineRect.bottom = rectLV.bottom;

        ExtTextOutW(hDC, 0, 0, ETO_OPAQUE, 
                    &LineRect, NULL, NULL, NULL);
        Counter++;
    }

    //Horizontal lines
    ItemRect.left = LVIR_BOUNDS;
    SendMessage(g_hWndListView, LVM_GETITEMRECT, 
                0,(LPARAM)&ItemRect);
    ItemHeight = ItemRect.bottom - ItemRect.top;

    LineIndex = rectHeader.bottom - 1;
    LineRect.bottom = LineIndex;

    while (LineIndex < rectLV.bottom)
    {
        LineIndex = LineIndex + borderWidth;
        LineRect.left = 0;
        LineRect.top = LineIndex - 1;
        LineRect.right = rectLV.right;
        LineRect.bottom = LineIndex;
        ExtTextOutW(hDC, 0, 0, ETO_OPAQUE, 
                    &LineRect, NULL, NULL, NULL);
        LineIndex = (LineRect.bottom - 1) + ItemHeight;
    }

    SetBkColor(hDC, oldBkColor);
}
int ListView_CustomDraw(LPNMLVCUSTOMDRAW lpnmlv)
{
    switch (lpnmlv->nmcd.dwDrawStage)
    {
    case CDDS_PREPAINT:
        return CDRF_NOTIFYPOSTPAINT;
        break;
  
    case CDDS_POSTPAINT:
        ListView_DrawGridLines(lpnmlv->nmcd.hdc, RGB(89, 89, 89));
        return CDRF_SKIPDEFAULT;
        break;
    default:
        return CDRF_DODEFAULT;
    }
}
LRESULT CALLBACK MainProc(HWND hWnd, UINT msg, 
                          WPARAM wParam, LPARAM lParam) {
    RECT rect;
    
    switch (msg) {

    case WM_CREATE: {

        CreateListview(hWnd);
        break;
    }
       
    case WM_NOTIFY:
    {
        LPNMHDR nmhdr = (LPNMHDR)lParam;

        if (nmhdr->code == NM_CUSTOMDRAW && 
            nmhdr->hwndFrom == g_hWndListView)
        {
            LPNMLVCUSTOMDRAW lpNMCustomDraw = 
                             (LPNMLVCUSTOMDRAW)lParam;
            return ListView_CustomDraw(lpNMCustomDraw);
        }       

        break;
    }

    case WM_SIZE:
    {
        GetClientRect(hWnd, &rect);
        SetWindowPos(g_hWndListView, NULL, 0, 0, 
                     rect.right - 2, rect.bottom - 2, 
                     SWP_NOMOVE | SWP_NOZORDER | SWP_NOACTIVATE);
        break;
    }
    case WM_DESTROY: {

        PostQuitMessage(0);
        break;
    }
            
    default:

        return DefWindowProc(hWnd, msg, wParam, lParam);
    }

    return 0;
}