ImageTransparency.cs
// 完毕:
using System;
using System.IO;
using System.Drawing;
using GrapeCity.Documents.Pdf;
using GrapeCity.Documents.Text;
using GrapeCity.Documents.Drawing;
using GCTEXT = GrapeCity.Documents.Text;
using GCDRAW = GrapeCity.Documents.Drawing;

namespace DsPdfWeb.Demos
{
    // 该示例演示了 GcDocs.Pdf 渲染的能力
    // 使用指定透明度(不透明度)的图像。
    public class ImageTransparency
    {
        public int CreatePDF(Stream stream)
        {
            var doc = new GcPdfDocument();
            var page = doc.NewPage();
            var g = page.Graphics;

            var rc = Common.Util.AddNote(
                "GcPdfGraphics.DrawImage() 方法允许渲染具有指定不透明度的图像。" +
                "",
                page);

            var tl = g.CreateTextLayout();
            tl.DefaultFormat.Font = StandardFonts.Times;
            tl.DefaultFormat.FontSize = 12;
            tl.MaxWidth = page.Size.Width;
            tl.MaxHeight = page.Size.Height;
            tl.MarginAll = 36;
            tl.MarginTop += rc.Bottom;
            tl.Append(Common.Util.LoremIpsum(2));
            tl.PerformLayout(true);
            g.DrawTextLayout(tl, PointF.Empty);

            using (var image = GCDRAW.Image.FromFile(Path.Combine("Resources", "Images", "puffins.jpg")))
            {
                var imageRc = new RectangleF(tl.MarginLeft, tl.MarginTop, 144, 144);
                // 不透明度0.2:
                g.DrawImage(image, imageRc, null, ImageAlign.ScaleImage, 0.2f);
                imageRc.Offset(imageRc.Width + 36, 0);
                // 不透明度0.5:
                g.DrawImage(image, imageRc, null, ImageAlign.ScaleImage, 0.5f);
                imageRc.Offset(imageRc.Width + 36, 0);
                // 不透明度 1(默认):
                g.DrawImage(image, imageRc, null, ImageAlign.ScaleImage);

                // 注意:我们必须在处理文档中使用的图像之前保存文档:
                doc.Save(stream);
            }
            return doc.Pages.Count;
        }
    }
}