using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace HF.SHOP.Common
{
    public class ImageHelper
    {
        /// <summary>
        /// 缩放图片
        /// </summary>
        /// <param name="img"></param>
        /// <param name="w"></param>
        /// <param name="h"></param>
        /// <returns></returns>
        public static Bitmap ResizeImage(Image img, int w, int h)
        {
            Bitmap resizeBitmap = new Bitmap(img, w, h);

            return resizeBitmap;
        }

        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param Name="originalImagePath">源图路径（物理路径）</param>
        /// <param Name="thumbnailPath">缩略图路径（物理路径）</param>
        /// <param Name="width">缩略图宽度</param>
        /// <param Name="height">缩略图高度</param>
        /// <param Name="mode">生成缩略图的方式</param>    
        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
        {
            System.Drawing.Image originalImage = System.Drawing.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
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            System.Drawing.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(System.Drawing.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 System.Drawing.Rectangle(0, 0, towidth, toheight),
                new System.Drawing.Rectangle(x, y, ow, oh),
                System.Drawing.GraphicsUnit.Pixel);

            try
            {
                //以jpg格式保存缩略图
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
                // File.Delete(originalImagePath);//删除原图
            }
        }

        /// <summary>
        /// 剪切图片
        /// </summary>
        /// <param name="img"></param>
        /// <param name="x"></param>
        /// <param name="y"></param>
        /// <param name="w"></param>
        /// <param name="h"></param>
        /// <returns></returns>
        public static Bitmap CropImage(Image img, int x, int y, int w, int h)
        {
            Rectangle resizeRect = new Rectangle(x, y, w, h);
            Bitmap cropBitmap = new Bitmap(w, h);
            Graphics cropG = Graphics.FromImage(cropBitmap);

            cropG.DrawImage(img, 0, 0, resizeRect, GraphicsUnit.Pixel);
            cropG.Dispose();

            return cropBitmap;
        }

        /// <summary>
        /// 获取图片文件名
        /// </summary>
        /// <returns></returns>
        public static string GetAutoImageName()
        {
            //Random rad = new Random();

            //return string.Format("{0}_{1}", DateTime.Now.ToString("yyyyMMddHHmmss"), rad.Next(1000, 10000).ToString());
            return DateTime.Now.Ticks.ToString();
        }
    }
}

图片帮助类