Itextsharp渐变背景

using System;
using System.IO;
using iTextSharp.text;
using iTextSharp.text.pdf;

namespace ITextSharpGradientBackground
{
    class Program
    {
        static void Main(string[] args)
        {
            // 创建文档
            Document document = new Document(PageSize.A4);
            // 创建PDF写入器
            PdfWriter writer = PdfWriter.GetInstance(document, new FileStream("gradient_background.pdf", FileMode.Create));
            // 打开文档
            document.Open();
            // 创建渐变背景
            PdfShading shading = PdfShading.SimpleAxial(writer, 0, 0, PageSize.A4.Width, PageSize.A4.Height, BaseColor.RED, BaseColor.BLUE);
            PdfShadingPattern pattern = new PdfShadingPattern(shading);
            // 设置渐变背景
            writer.PageEvent = new GradientBackground(pattern);
            // 添加文本
            document.Add(new Paragraph("Hello, world!"));
            // 关闭文档
            document.Close();
        }
    }

    class GradientBackground : PdfPageEventHelper
    {
        PdfShadingPattern _pattern;

        public GradientBackground(PdfShadingPattern pattern)
        {
            _pattern = pattern;
        }

        public override void OnOpenDocument(PdfWriter writer, Document document)
        {
            base.OnOpenDocument(writer, document);
            writer.DirectContent.SetShadingFill(_pattern);
        }
    }
}