How to rotate a drawn line by increasing the angle by using a timer?

Question

The problem is that the line also get shorter and I want to keep the line length. when it's rotating.

I'm using the method DrawLine and call it in the pictureBox1 paint event and it's drawing a line.

now I want to rotate the line in a circle without changing the center point and without leave lines behind only to rotate that line with the same radius.

like a doppler effect just to imagine what I mean by rotating.

not sure if to use a timer for that and how to do it?

private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            Graphics mygraph = e.Graphics;
            mygraph.DrawLine(mypen, 250, 250, x, 150);
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            x++;
            pictureBox1.Invalidate();
        }

Answer 1

I used a .png in my test to avoid drawing the line.

By drawing the line, you can do something like this with a Timer :

At beginning (Form1_Load) :

            var timer1 = new System.Windows.Forms.Timer();
            timer1.Tick += new EventHandler(TimerEventProcessor);
            timer1.Interval = 10;
            timer1.Start();

then :

        private void TimerEventProcessor(Object myObject, EventArgs myEventArgs)
        {
            pictureBox1.Invalidate();
        }

        float m_nAngle = 0;

        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            var g = e.Graphics;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.Clear(Color.Yellow);
            var rect = this.pictureBox1.ClientRectangle;
            g.TranslateTransform(rect.Left + rect.Width / 2, rect.Top + rect.Height / 2);
            g.RotateTransform(m_nAngle);
            m_nAngle += 1;
            if (m_nAngle >= 360) m_nAngle = 0;
            using (var penLine = new Pen(Color.Red, 2))
                g.DrawLine(penLine, 0, 0, 0, -rect.Height / 2);           
        }