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);
                }
            }
        }