protected override void OnSizeChanged(int w, int h, int oldw, int oldh)
{
base.OnSizeChanged(w, h, oldw, oldh);
var xpad = (float)(PaddingLeft + PaddingRight);
var ypad = (float)(PaddingTop + PaddingBottom);
var ww = w - xpad;
var hh = h - ypad;
_bounds = new RectF(0f, 0f, ww, hh);
_bounds.OffsetTo(PaddingLeft, PaddingTop);
}