C#实现图片旋转

　　　　 private const string IMAGEFILE = "FocusPoint.JPG";
        private static int MyAngle = 0;     //旋转角度[-360,360]

        private void Page_Load(object sender, EventArgs e)
        {
            Image img;
            FileStream fs;

            fs = new FileStream(IMAGEFILE, FileMode.Open, FileAccess.Read);
            img = Bitmap.FromStream(fs);
            fs.Close();
            pictureBox1.Image = img;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            MyAngle = 90;
            //MyAngle += 90;
            //if (MyAngle > 360) MyAngle = 90;
            pictureBox1.Image = RotateImg(GetSourceImg(IMAGEFILE), MyAngle);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            MyAngle = -90;
            //MyAngle += -90;
            //if (MyAngle < -360) MyAngle = -90;
            //pictureBox1.Image = RotateImg(Bitmap.FromFile(IMAGEFILE), MyAngle);
            pictureBox1.Image = RotateImg(IMAGEFILE, MyAngle);
        }

        #region 图片旋转函数
        /// <summary>
        /// 以逆时针为方向对图像进行旋转
        /// </summary>
        /// <param name="b">位图流</param>
        /// <param name="angle">旋转角度[0,360](前台给的)</param>
        /// <returns></returns>
        public Image RotateImg(Image b, int angle)
        {
            angle = angle % 360;
            //弧度转换
            double radian = angle * Math.PI / 180.0;
            double cos = Math.Cos(radian);
            double sin = Math.Sin(radian);

            //原图的宽和高
            int w = b.Width;
            int h = b.Height;
            int W = (int)(Math.Max(Math.Abs(w * cos - h * sin), Math.Abs(w * cos + h * sin)));
            int H = (int)(Math.Max(Math.Abs(w * sin - h * cos), Math.Abs(w * sin + h * cos)));

            //目标位图
            Bitmap dsImage = new Bitmap(W, H);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(dsImage);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.Bilinear;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            //计算偏移量
            Point Offset = new Point((W - w) / 2, (H - h) / 2);

            //构造图像显示区域：让图像的中心与窗口的中心点一致
            Rectangle rect = new Rectangle(Offset.X, Offset.Y, w, h);
            Point center = new Point(rect.X + rect.Width / 2, rect.Y + rect.Height / 2);
            g.TranslateTransform(center.X, center.Y);
            g.RotateTransform(360 - angle);

            //恢复图像在水平和垂直方向的平移
            g.TranslateTransform(-center.X, -center.Y);
            g.DrawImage(b, rect);

            //重至绘图的所有变换
            g.ResetTransform();
            g.Save();
            g.Dispose();

            //保存旋转后的图片
            b.Dispose();
            dsImage.Save("FocusPoint.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
            return dsImage;
        }

        public Image RotateImg(string filename, int angle)
        {
            return RotateImg(GetSourceImg(filename), angle);
        }

        public Image GetSourceImg(string filename)
        {
            Image img;
            img = Bitmap.FromFile(filename);
            return img;
        }

        #endregion 图片旋转函数