绘制当前屏幕
e.Graphics.CopyFromScreen(new Point(10,10)截屏起点, new Point(140, 140)绘制起点,
new Size(100,100)截取大小, CopyPixelOperation.MergeCopy显示模式);
特殊的参数:
当前窗口位置:this.Location
全屏大小:Screen.GetWorkingArea(this).Size
e.Graphics.CopyFromScreen(this.Location, new Point(140, 140),
new Size(100,200), CopyPixelOperation.MergeCopy);