c#不使用系统api实现可以指定区域屏幕截屏功能

//截取全屏图象
        private void btnFullScreen_Click(object sender, EventArgs e)
        {
            //创建图象，保存将来截取的图象
            Bitmap image = new Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height);
            Graphics imgGraphics = Graphics.FromImage(image);
            //设置截屏区域
            imgGraphics.CopyFromScreen(0, 0, 0, 0, new Size(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height));
            //保存
            SaveImage(image);
        }

//保存图象文件
        private void SaveImage(Image image)
        {
            if (saveFileDialog.ShowDialog(this) == DialogResult.OK)
            {
                string fileName = saveFileDialog.FileName;
                string extension = Path.GetExtension(fileName);
                if (extension == ".jpg")
                {
                    image.Save(fileName, ImageFormat.Jpeg);
                }
                else
                {
                    image.Save(fileName, ImageFormat.Bmp);
                }
            }
        }