Error with GDI+ Sample

[ahmed17]

Hi Guys,


I am try to draw line and i want to make line rotate 360 degree and each degree changed regarding as timer intervals.

  double x1, y1, r;
        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = this.CreateGraphics();
            Pen p = new Pen(Color.Red);
            g.DrawEllipse(p, 0, 0, 398, 398);
            Pen p1 = new Pen(Color.Black);



            for (double theta = 20; r < 360; theta++)
            {
                theta = theta * (Math.PI / 360);
                x1 = r * (Math.Cos(theta));
                y1 = r * (Math.Sin(theta));
                g.DrawLine(p1, (float)x1, (float)y1, 200, 198);
            }
           
        }

[BigEd781]

You should not be doing all of the drawing inside of a loop in the paint event. That code will run very quickly and you won't see anything at all. Painting is an incremental process; for each tick of the time you should redraw the line once. So, store the last point on the edge of the circle externally from the paint method and increment it before calling Invalidate() once again. Each call to OnPaint() should be a single refresh, a single frame.

[ahmed17]

I am try to do this change but error .......

[BigEd781]

What error? You could at least tell us what error you are encountering, we are not psychic.