C# 绘图

http://www.cnblogs.com/peterzb/archive/2009/07/19/1526555.html

1. 生成缩略图.

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath">源路径</param>
        /// <param name="thumbnailPath">目标路径</param>
        /// <param name="width">宽</param>
        /// <param name="height">高</param>
        /// <param name="mode">缩略模式</param>
        public static Image MakeThumbnail(string originalImagePath, int width, int height, string mode)
        {
            Image originalImage = Image.FromFile(originalImagePath);
 
            int towidth = width;
            int toheight = height;
 
            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;
 
            switch (mode)
            {
                case "HW"://指定高宽缩放（可能变形）                
                    break;
                case "W"://指定宽，高按比例                    
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高宽裁减（不变形）                
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                default:
                    break;
            }
 
            //新建一个bmp图片
            Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
 
            //新建一个画板
            Graphics g = System.Drawing.Graphics.FromImage(bitmap);
 
            //设置高质量插值法
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
 
            //设置高质量,低速度呈现平滑程度
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
 
            //清空画布并以透明背景色填充
            g.Clear(Color.Transparent);
 
            //在指定位置并且按指定大小绘制原图片的指定部分
            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
                new Rectangle(x, y, ow, oh),
                GraphicsUnit.Pixel);
            return bitmap;
        }