C# 如何添加PPT背景（纯色背景、渐变色背景、图片背景）

using Spire.Presentation;
using Spire.Presentation.Drawing;
using System.Drawing;

namespace AddBackground_PPT
{
    class Program
    {
        static void Main(string[] args)
        {
            //实例化Presentation类，加载PowerPoint文档
            Presentation ppt = new Presentation();
            ppt.LoadFromFile("test.pptx");

            //设置文档的背景填充模式为纯色填充
            ppt.Slides[0].SlideBackground.Type = BackgroundType.Custom;
            ppt.Slides[0].SlideBackground.Fill.FillType = FillFormatType.Solid;
            ppt.Slides[0].SlideBackground.Fill.SolidColor.Color = Color.Pink;

            //设置文档的背景填充模式为渐变色填充
            ppt.Slides[1].SlideBackground.Type = BackgroundType.Custom;
            ppt.Slides[1].SlideBackground.Fill.FillType = FillFormatType.Gradient;
            ppt.Slides[1].SlideBackground.Fill.Gradient.GradientStops.Append(0f, KnownColors.Yellow);
            ppt.Slides[1].SlideBackground.Fill.Gradient.GradientStops.Append(1f, KnownColors.Orange);

            //设置幻灯片背景色为图片背景
            ppt.Slides[2].SlideBackground.Type = Spire.Presentation.Drawing.BackgroundType.Custom;
            ppt.Slides[2].SlideBackground.Fill.FillType = FillFormatType.Picture;
            ppt.Slides[2].SlideBackground.Fill.PictureFill.FillType = PictureFillType.Stretch;
            //加载图片作为幻灯片背景
            Image img = Image.FromFile("green.png");
            IImageData image = ppt.Images.Append(img);
            ppt.Slides[2].SlideBackground.Fill.PictureFill.Picture.EmbedImage = image;

            //保存并打开文档
            ppt.SaveToFile("result.pptx", FileFormat.Pptx2010);
            System.Diagnostics.Process.Start("result.pptx");
        }
    }
}