window content disapperas after moving

hi there
im completely new to opengl and i have no clue at all xD
im trying to get it to work on ubuntu linux with c# and tao.

finally it works but when i move the window around or cover it with another window the drawings disappear.

i read that this can be solved via the reshape function callback but it seems not to do anything.

i guess its just a minor flaw of mine but as i have no experience i cant find it.

this is my complete code:

using System;
using System.Collections.Generic;
using Tao.FreeGlut;
using Tao.OpenGl;

namespace FreeGlutExample
    static class Program
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        static void Main()
            // initialise glut library

            // initialise the window settings
            Glut.glutInitDisplayMode(Glut.GLUT_RGB | Glut.GLUT_SINGLE);
            Glut.glutInitWindowSize(400, 400);
			Glut.glutInitWindowPosition(400, 200);
            Glut.glutCreateWindow("GdgDV Uebung 2");

			Glu.gluOrtho2D(0,400,400,0);        /* how object is mapped to window */			
            // do our own initialisation

            // set the callback functions
            Glut.glutDisplayFunc(new Glut.DisplayCallback(Display));
            Glut.glutReshapeFunc(new Glut.ReshapeCallback(Reshape));

            // enter the main loop. Glut will be here permanently from now on
            // until we quit the program

        /// <summary>
        /// initialises the openGL settings
        /// </summary>
        private static void Init()
			Gl.glClearColor(1.0f, 0.0f, 0.0f, 0.0f);

        /// <summary>
        /// called when the window changes size
        /// </summary>
        /// <param name="w">new width of the window</param>
        /// <param name="h">ne height of the window</param>
        private static void Reshape(int w, int h)
            if (h == 0) h = 1;

        /// <summary>
        /// the display callback function 
        /// </summary>
        private static void Display()

			// 2 kreis in orange
			Gl.glColor3f(1, 0.5f, 0);
			circle(200, 200, 200, 360, 0);
			// 1 fünfeck in gelb
			Gl.glColor3f(1, 1, 0);
			circle(200, 200, 200, 5, -1f);		
			// 3 kreis in blau
			Gl.glColor3f(0, 1, 1);
			circle(200, 200, 162, 360, 0);			

			// 4 fünfeck in gelb
			Gl.glColor3f(1, 1, 0);
			circle(200, 200, 162, 5, -1f);			
		public static void circle(float center_x, float center_y, float radius, float steps, float rotation) {
			double PI2 = Math.PI*2;		
			float x = 0.0f;
			float y = 0.0f;

			for( double theta = rotation; theta < PI2; theta += PI2 / steps ) {
				x = (float) (center_x + ( Math.Cos( theta ) * radius));
				y = (float) (center_y + ( Math.Sin( theta ) * radius));
				Gl.glVertex2f(x, y);

it would be great if you could help a lost beginner :wink:

thanks in advance

Redrawing the window all the time could help:

void myIdleFunction()


In addition move this to the reshape function:


and call also glViewport to set the new viewport size.

thanks a lot. this and activating double buffering works just fine.

maybe im doing it wrong but this causes an empty window…

You do it wrong, your Reshape function is pretty useless in the above code and do not fulfill his role in case of window resizing.

Look for glut example code with Google, you will find many valid glut base sample codes.