WYSIWYG Progress Circle for .NET Framework (C#)

private System.Collections.Generic.Dictionary<Color, SolidBrush> _brushCache =
           new System.Collections.Generic.Dictionary<Color,SolidBrush>();

       private void DrawFilledArc (Graphics grp, Color color, int startAngle)
       {
           grp.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

           Rectangle main = this.ClientRectangle;

           // If there is no region to be drawn, then this method terminates itself
           if (main.Width - (2*this._ringThickness) < 1 || main.Height -(2*this._ringThickness) <= 1)
               return;

           // Calculates the region that will be filled

           using (GraphicsPath outerPath = new GraphicsPath())
           {
               outerPath.AddPie(main, startAngle, this.PieAngle);

               Rectangle sub = new Rectangle(main.X + this._ringThickness, main.Y + this._ringThickness, main.Width - (2 * this._ringThickness), main.Height - (2 * this._ringThickness));

               using (GraphicsPath innerPath = new GraphicsPath())
               {
                   innerPath.AddPie(sub, startAngle - 1, this.PieAngle + 2);

                   using (System.Drawing.Region mainRegion = new Region(outerPath))
                   {
                       using (System.Drawing.Region subRegion = new Region(innerPath))
                       {

                           mainRegion.Exclude(subRegion);

                           SolidBrush targetBrush;

                           if (_brushCache.ContainsKey(color))
                           {
                               targetBrush = _brushCache[color];
                           }
                           else
                           {
                               targetBrush = new SolidBrush(color);
                               _brushCache.Add(color,targetBrush);
                           }
                           // Fill that region
                           grp.FillRegion(targetBrush, mainRegion);
                       }
                   }
               }
           }
       }