public delegate void PaintHandler(DrawingContext drawing_context);
        public event PaintHandler Paint;
        protected override void OnRender(DrawingContext drawing_context)
        {
            base.OnRender(drawing_context);
            if (Paint != null)
                Paint(drawing_context);
        }

private void uc_Paint(DrawingContext drawing_context)
        {
            if (list != null)
                if (list.Count > 0)
                    foreach (Geometry item in list)
                    {
                        drawing_context.DrawGeometry(Brushes.Green, new Pen(Brushes.Red, 1), item);
                    }
        }

private void button2_Click(object sender, EventArgs e)
        {
            foreach (Geometry item in list)
            {
                Transform mt = new ScaleTransform(1.5, 1.5);
                item.Transform = new MatrixTransform(Matrix.Multiply(item.Transform.Value, mt.Value));
            }
            uc.InvalidateVisual();
        }