什么是屏幕坐标？为何有时候要把坐标转换成屏幕坐标？


        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if(e.Button==MouseButtons.Left)
            {
                if (radioButton1.Checked == true)
                {
                    ControlPaint.DrawReversibleLine(PointToScreen(ps),PointToScreen(pe),Color.Black);
                    pe = e.Location;
                }
            }        }
这段程序为何要转换成屏幕坐标，不转换不行吗？