Created attachment 180 [details]
Runtime Version Check output, ran for all entries that appear in the test.bat script.

Without animator, GLCanvas does not constantly display its OpenGL scene. It displays either its component background or the scene.

To reproduce the bug, please run the test application below. When the frame is being resized by dragging its edge over, the canvas flickers between yellow and red (resp. its background and its scene). When the resize operation ends, it randomly leaves the canvas in either configuration (yellow or red).

I only reproduced that bug on a Win32 platform but I did not try any other platform. I can't objectively assume it but it may be reproducable on every platform as well.

Sample code to reproduce the bug:
package GLSLTest;

import java.awt.Color;
import java.awt.Component;
import java.awt.Frame;

import javax.media.opengl.GL;
import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.swing.BoxLayout;

public class Main
{
        static CanvasListener listener = new CanvasListener();

        public static void main(String[] args)
        {
                GLProfile.initSingleton();

                GLProfile profile = GLProfile.getMaxFixedFunc();
                GLCapabilities caps = new GLCapabilities(profile);
                GLCanvas canvas = new GLCanvas(caps);
                canvas.setBackground(Color.yellow);
                canvas.addGLEventListener(listener);

                Frame topLevelFrame = new Frame();
                topLevelFrame.setLayout(new BoxLayout(topLevelFrame, BoxLayout.Y_AXIS));
                topLevelFrame.add(canvas);
                topLevelFrame.setSize(400, 300);
                topLevelFrame.setVisible(true);

                // Animator animator = new Animator(canvas);
                // animator.start();

                canvas.display();
        }
}

class CanvasListener implements GLEventListener
{
        @Override
        public void display(GLAutoDrawable arg0)
        {
                GL2 gl = arg0.getGL().getGL2();
                gl.glClearColor(1.0f, 0.0f, 0.0f, 0.5f);
                gl.glClear(GL.GL_COLOR_BUFFER_BIT);

                System.out.println("display");
        }

        @Override
        public void dispose(GLAutoDrawable arg0)
        {
        }

        @Override
        public void init(GLAutoDrawable arg0)
        {
                Component canvas = (Component) arg0;
                System.out.println(canvas.getSize().toString());
        }

        @Override
        public void reshape(GLAutoDrawable arg0, int arg1, int arg2, int arg3, int arg4)
        {
        }
}