sub on_paint {
    my( $self, $event ) = @_;
    my $dc = Wx::PaintDC->new( $self );

    $dc->SetBrush( Wx::Brush->new( Wx::Colour->new( 0, 192, 0 ), wxSOLID ) );
    $dc->SetPen( Wx::Pen->new( Wx::Colour->new( 0, 0, 0 ), 1, wxSOLID ) );
    $dc->DrawRectangle( 0, 0, $self->GetSize->x, $self->GetSize->y );
}