缩略图

/// <summary>
        /// 缩略图
        /// </summary>
        /// <param name="srcImage">要缩略的图片</param>
        /// <param name="thumSize">要缩放的尺寸</param>
        /// <param name="mode">缩略模式</param>
        /// <param name="alignment">对齐方式</param>
        /// <returns>返回已经缩放的图片。</returns>
        public static Bitmap GetDistortionlessThumbnailImage(Image srcImage, SizeF thumSize, ThumbnailMode mode, ContentAlignment alignment)
        {
            //先取宽比例。
            float scale = (float)srcImage.Width / (float)thumSize.Width;
            //缩略模式
            switch (mode)
            {
                case ThumbnailMode.FullDistortionless:
                    if (srcImage.Height > srcImage.Width)
                    {
                        scale = (float)srcImage.Height / (float)thumSize.Height;
                    }
                    break;
                case ThumbnailMode.MaxDistortionless:
                    if (srcImage.Height / scale < thumSize.Height)
                    {
                        scale = (float)srcImage.Height / (float)thumSize.Height;
                    }
                    break;
            }
            SizeF newSzie = new SizeF(srcImage.Width / scale, srcImage.Height / scale);
            Bitmap result = new Bitmap((int)thumSize.Width, (int)thumSize.Height);
            using (Graphics g = Graphics.FromImage(result))
            {
                //背景颜色
                g.FillRectangle(Brushes.White, new RectangleF(PointF.Empty, thumSize));
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.PixelOffsetMode = PixelOffsetMode.HighQuality;
                g.CompositingMode = CompositingMode.SourceOver;
                g.CompositingQuality = CompositingQuality.HighQuality;
                g.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;
                //对齐方式
                RectangleF destRect;
                switch (alignment)
                {
                    case ContentAlignment.TopCenter:
                        destRect = new RectangleF(new PointF(-((newSzie.Width - thumSize.Width) / 2), 0), newSzie);
                        break;
                    case ContentAlignment.TopRight:
                        destRect = new RectangleF(new PointF(-(newSzie.Width - thumSize.Width), 0), newSzie);
                        break;
                    case ContentAlignment.MiddleLeft:
                        destRect = new RectangleF(new PointF(0, -((newSzie.Height - thumSize.Height) / 2)), newSzie);
                        break;
                    case ContentAlignment.MiddleCenter:
                        destRect = new RectangleF(new PointF(-((newSzie.Width - thumSize.Width) / 2), -((newSzie.Height - thumSize.Height) / 2)), newSzie);
                        break;
                    case ContentAlignment.MiddleRight:
                        destRect = new RectangleF(new PointF(-(newSzie.Width - thumSize.Width), -((newSzie.Height - thumSize.Height) / 2)), newSzie);
                        break;
                    case ContentAlignment.BottomLeft:
                        destRect = new RectangleF(new PointF(0, -(newSzie.Height - thumSize.Height)), newSzie);
                        break;
                    case ContentAlignment.BottomCenter:
                        destRect = new RectangleF(new PointF(-((newSzie.Width - thumSize.Width) / 2), -(newSzie.Height - thumSize.Height)), newSzie);
                        break;
                    case ContentAlignment.BottomRight:
                        destRect = new RectangleF(new PointF(-(newSzie.Width - thumSize.Width), -(newSzie.Height - thumSize.Height)), newSzie);
                        break;
                    default:
                        destRect = new RectangleF(PointF.Empty, newSzie);
                        break;
                }
                g.DrawImage(srcImage, destRect, new RectangleF(PointF.Empty, srcImage.Size), GraphicsUnit.Pixel);
                g.Dispose();
            }
            return result;
        }