private void DetermineRange() { RectangleD worldRect = Owner.WorldRect; Rectangle canvasRect = Owner.CanvasRect; PointF tf = PointD.Truncate(Conversion.ScreenToWorld(new PointD(0.0, 0.0), worldRect, canvasRect)); PointF tf2 = PointD.Ceiling(Conversion.ScreenToWorld(new PointD(AxisRect.Right, 0.0), worldRect, canvasRect)); StartIndex = (int)tf.X; LastIndex = (int)tf2.X; }