How to align button at the centre of a cell?

public class SampleButtonCellModel : GridStaticCellModel
{
   protected SampleButtonCellModel(SerializationInfo info, StreamingContext context)
             : base(info, context)
   {
   }
   public SampleButtonCellModel(GridModel grid)
          : base(grid)
   {
       AllowFloating = false;
       ButtonBarSize = new Size(120, 120);
   }
 
   public override GridCellRendererBase CreateRenderer(GridControlBase control)
   {
       return new SampleButtonCellRenderer(control, this);
   }
}

Public Class SampleButtonCellModel
 Inherits GridStaticCellModel
   Protected Sub New(ByVal info As SerializationInfo, ByVal context As StreamingContext)
    MyBase.New(info, context)
   End Sub
   Public Sub New(ByVal grid As GridModel)
    MyBase.New(grid)
   AllowFloating = False
   ButtonBarSize = New Size(120, 120)
   End Sub
 
   Public Overrides Function CreateRenderer(ByVal control As GridControlBase) As GridCellRendererBase
   Return New SampleButtonCellRenderer(control, Me)
   End Function
End Class

public class SampleButtonCellRenderer : GridStaticCellRenderer
{
    protected GridCellButton sampleButton;
    public SampleButtonCellRenderer(GridControlBase grid, GridCellModelBase cellModel)
            : base(grid, cellModel)
    {
       AddButton(this.sampleButton = new GridCellButton(this));
       this.ForceRefreshOnActivateCell = true;
    }
    protected SampleButtonCellRenderer(GridControlBase grid, GridCellModelBase cellModel, GridCellButton button)
            : base(grid, cellModel)
    {
        this.sampleButton = button;
    }
    protected override void OnDraw(Graphics g, Rectangle clientRectangle, int rowIndex, int colIndex, GridStyleInfo style)
    {
        base.OnDraw(g, clientRectangle, rowIndex, colIndex, style);
    }
 
    protected override Rectangle OnLayout(int rowIndex, int colIndex, GridStyleInfo style, Rectangle innerBounds, Rectangle[] buttonsBounds)
    {
       TraceUtil.TraceCurrentMethodInfo(rowIndex, colIndex, style, innerBounds, buttonsBounds);
       Rectangle rect = GridUtil.CenterInRect(innerBounds, this.Model.ButtonBarSize);
       int width = rect.Width / 2;
       buttonsBounds[0] = new Rectangle(rect.X + width / 2, rect.Y, width, rect.Height);
       return innerBounds;
    }
}

Public Class SampleButtonCellRenderer
 Inherits GridStaticCellRenderer
   Protected sampleButton As GridCellButton
   Public Sub New(ByVal grid As GridControlBase, ByVal cellModel As GridCellModelBase)
    MyBase.New(grid, cellModel)
   AddButton(Me.sampleButton = New GridCellButton(Me))
   Me.ForceRefreshOnActivateCell = True
   End Sub
   Protected Sub New(ByVal grid As GridControlBase, ByVal cellModel As GridCellModelBase, ByVal button As GridCellButton)
    MyBase.New(grid, cellModel)
    Me.sampleButton = button
   End Sub
   Protected Overrides Sub OnDraw(ByVal g As Graphics, ByVal clientRectangle As Rectangle, ByVal rowIndex As Integer, ByVal colIndex As Integer, ByVal style As GridStyleInfo)
    MyBase.OnDraw(g, clientRectangle, rowIndex, colIndex, style)
   End Sub
 
   Protected Overrides Function OnLayout(ByVal rowIndex As Integer, ByVal colIndex As Integer, ByVal style As GridStyleInfo, ByVal innerBounds As Rectangle, ByVal buttonsBounds() As Rectangle) As Rectangle
    TraceUtil.TraceCurrentMethodInfo(rowIndex, colIndex, style, innerBounds, buttonsBounds)
    Dim rect As Rectangle = GridUtil.CenterInRect(innerBounds, Me.Model.ButtonBarSize)
    Dim width As Integer = rect.Width \ 2
    buttonsBounds(0) = New Rectangle(rect.X + width \ 2, rect.Y, width, rect.Height)
    Return innerBounds
   End Function
End Class

// form()
this.gridControl1.CellModels.Add("SampleButton", new SampleButtonCellModel(this.gridControl1.Model));
this.gridControl1[2, 2].CellValue = "";
this.gridControl1[2, 2].CellType = "SampleButton";

' form()
Me.gridControl1.CellModels.Add("SampleButton", New SampleButtonCellModel(Me.gridControl1.Model))
Me.gridControl1(2, 2).CellValue = ""
Me.gridControl1(2, 2).CellType = "SampleButton"