Прокрутка в ScrollBox

if Msg.WParam < 0 then 
  zDelta := -10 
else 
  zDelta := 10;

unit Unit1;
 
interface
 
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ComCtrls;
 
type
  TForm1 = class(TForm)
    ScrollBox1: TScrollBox;
    PageScroller1: TPageScroller;
    procedure FormCreate(Sender: TObject);
  private
    procedure WMMOUSEWHEEL(var Msg: TMessage); message WM_MOUSEWHEEL;
  public
    { Public declarations }
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
procedure TForm1.FormCreate(Sender: TObject);
var
  vI: Integer;
  vRadioButton: TRadioButton;
begin
  for vI := 0 to 15 do
  begin
    vRadioButton := TRadioButton.Create(ScrollBox1);
    vRadioButton.Parent := ScrollBox1;
    vRadioButton.AlignWithMargins := True;
    vRadioButton.Margins.Left := 5;
    vRadioButton.Caption := 'Btn ' + IntToStr(vI);
    vRadioButton.Align := alTop;
    vRadioButton.Visible := True;
  end;
end;
 
procedure TForm1.WMMOUSEWHEEL(var Msg: TMessage);
var
  zDelta: Integer;
begin
  inherited;
//  if WindowFromPoint(Mouse.CursorPos) <> ScrollBox1.Handle then Exit;
  if Msg.WParam < 0 then zDelta := -10 else zDelta := 10;
  with ScrollBox1 do
  begin
    if ((VertScrollBar.Position = 0) and
        (zDelta > 0)) or
       ((VertScrollBar.Position = VertScrollBar.Range - ClientHeight) and
        (zDelta < 0)) then Exit;
    ScrollBy(0, zDelta);
    VertScrollBar.Position := VertScrollBar.Position - zDelta;
  end;
end;
 
end.