StingGrid - Объеденение ячеек

//Unit1.h
#ifndef Unit1H
#define Unit1H
//---------------------------------------------------------------------------
#include <Classes.hpp>
#include <Controls.hpp>
#include <StdCtrls.hpp>
#include <Forms.hpp>
#include <Grids.hpp>
//---------------------------------------------------------------------------
class TForm1 : public TForm
{
__published:    // IDE-managed Components
    TStringGrid *StringGrid1;

private:    // User declarations
    TWndMethod OldGridProc;
    void __fastcall NewGridProc(TMessage &Msg);
public:     // User declarations
    __fastcall TForm1(TComponent* Owner);
};
//---------------------------------------------------------------------------
extern PACKAGE TForm1 *Form1;
//---------------------------------------------------------------------------
#endif

//Unit1.cpp
#include <vcl.h>
#pragma hdrstop

#include "Unit1.h"
//---------------------------------------------------------------------------
#pragma package(smart_init)
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
    : TForm(Owner)
{
    OldGridProc = StringGrid1->WindowProc;
    StringGrid1->WindowProc = NewGridProc;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::NewGridProc(TMessage &Msg)
{
    TRect Rect1, Rect2, Rect;
    String Caption;
    int CaptionLength;

    switch (Msg.Msg)
    {
        case WM_PAINT:
        {
            OldGridProc(Msg);

            Rect1 = StringGrid1->CellRect(1, 1);
            Rect2 = StringGrid1->CellRect(2, 1);
            ::UnionRect(&Rect, &Rect1, &Rect2);
            StringGrid1->Canvas->Brush->Color = StringGrid1->FixedColor;
            StringGrid1->Canvas->FillRect(Rect);
            Frame3D(StringGrid1->Canvas, Rect, clBtnHighlight, clWindowFrame, 1);
            Caption = "Union cells";
            CaptionLength = Caption.Length();
            ::SetBkMode(StringGrid1->Canvas->Handle, TRANSPARENT );
            ::DrawText(StringGrid1->Canvas->Handle, Caption.c_str(), CaptionLength, &Rect, DT_SINGLELINE | DT_CENTER | DT_VCENTER );

            Msg.Result = 0;

            return;
        }

        case WM_DESTROY:
        {

            StringGrid1->WindowProc = OldGridProc;

            break;
        }
    }
    OldGridProc(Msg);
}