public override void WriteFunctionDictionary(PDFContextBase context, PDFWriter writer)
        {
            writer.BeginDictionary();
            writer.WriteDictionaryNumberEntry("FunctionType", 2);

            writer.BeginDictionaryEntry("Domain");
            writer.WriteArrayRealEntries(this.DomainStart, this.DomainEnd);
            writer.EndDictionaryEntry();

            writer.BeginDictionaryEntry("C0");
            writer.WriteArrayRealEntries(this.ColorZero.Red.Value, this.ColorZero.Green.Value, this.ColorZero.Blue.Value);
            writer.EndDictionaryEntry();

            writer.BeginDictionaryEntry("C1");
            writer.WriteArrayRealEntries(this.ColorOne.Red.Value, this.ColorOne.Green.Value, this.ColorOne.Blue.Value);
            writer.EndDictionaryEntry();

            writer.WriteDictionaryRealEntry("N", this.Exponent);
            writer.EndDictionary(); //function
        }
        //
        // methods
        //

        #region protected override PDFObjectRef DoRenderToPDF(PDFContextBase context, PDFWriter writer)

        /// <summary>
        /// Renders the tiling image
        /// </summary>
        /// <param name="context"></param>
        /// <param name="writer"></param>
        /// <returns></returns>
        protected override PDFObjectRef DoRenderToPDF(PDFContextBase context, PDFWriter writer)
        {
            IStreamFilter[] filters = writer.DefaultStreamFilters;
            PDFObjectRef    pattern = writer.BeginObject();

            writer.BeginDictionary();
            writer.WriteDictionaryNameEntry("Type", "Pattern");
            writer.WriteDictionaryNumberEntry("PatternType", (int)this.PatternType);
            writer.WriteDictionaryNumberEntry("PaintType", (int)this.PaintType);
            writer.WriteDictionaryNumberEntry("TilingType", (int)this.TilingType);
            writer.BeginDictionaryEntry("BBox");

            PDFPoint offset = new PDFPoint(this.Start.X, this.Start.Y - this.ImageSize.Height);// this.Start;
            PDFSize  size   = this.ImageSize;

            PDFSize graphicsSize = new PDFSize(size.Width + offset.X, size.Height + offset.Y);

            writer.WriteArrayRealEntries(true, offset.X.PointsValue,
                                         offset.Y.PointsValue,
                                         offset.X.PointsValue + size.Width.PointsValue,
                                         offset.Y.PointsValue + size.Height.PointsValue);

            writer.EndDictionaryEntry();

            writer.WriteDictionaryRealEntry("XStep", this.Step.Width.PointsValue);
            writer.WriteDictionaryRealEntry("YStep", this.Step.Height.PointsValue);

            PDFObjectRef all = this.Resources.WriteResourceList(context, writer);

            writer.WriteDictionaryObjectRefEntry("Resources", all);

            writer.BeginStream(pattern);

            using (PDFGraphics g = PDFGraphics.Create(writer, false, this, DrawingOrigin.TopLeft,
                                                      graphicsSize, context))
            {
                offset = new PDFPoint(offset.X, 0.0);
                g.PaintImageRef(this.Image, size, offset);
            }
            long len = writer.EndStream();

            if (null != filters && filters.Length > 0)
            {
                writer.BeginDictionaryEntry("Length");
                writer.WriteNumberS(len);
                writer.EndDictionaryEntry();
                writer.BeginDictionaryEntry("Filter");
                writer.BeginArray();
                foreach (IStreamFilter filter in filters)
                {
                    writer.BeginArrayEntry();
                    writer.WriteName(filter.FilterName);
                    writer.EndArrayEntry();
                }
                writer.EndArray();
                writer.EndDictionaryEntry();
            }
            else
            {
                writer.BeginDictionaryEntry("Length");
                writer.WriteNumberS(len);
                writer.EndDictionaryEntry();
            }

            writer.EndDictionary();
            writer.EndObject();

            return(pattern);
        }