How to attach opengl display to a JFrame and dispose of it properly?

Question

How can i attach the OpenGl display to a JFrame and so that when i close the JFrame is destroys the display? Here is my code so far:

package test.core;


import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Component;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;
import org.lwjgl.opengl.GL11;

import static org.lwjgl.opengl.GL11.*;

public class Main {



    private static CreateCanvas canvas;
    private static CreateFrame frame;

    private static int width = 800;
    private static int height = 600;

    public static void main(String[] args) throws InterruptedException {
        startFrames();

        startDisplay();

    }

    public static void cleanUp() {
        Display.destroy();
    }

    private static void startDisplay() {
        try
        {
            Display.setParent(canvas);
            Display.create();
        }catch(LWJGLException ex)
        {
            Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
    private static void startFrames()
    {
        Runnable r = new Runnable(){
            @Override
            public void run(){
                frame = new CreateFrame();
                JButton button = new JButton("BUTTON");
                canvas = new CreateCanvas();
                JPanel panel = frame.panel;

                panel.add(canvas);
                panel.add(button);
                frame.add(panel);

                canvas.setSize(300, 300);
                frame.setSize(width, height);

                frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);

                WindowListener listen = new WindowAdapter(){
                    @Override
                    public void windowClosing(WindowEvent we){
                        int result = JOptionPane.showConfirmDialog(frame, "Do you want to quit the Application?");
                        if(result == JOptionPane.OK_OPTION){
                            frame.setVisible(false);
                            cleanUp();
                            frame.dispose();
                        }
                    }
                };

                frame.addWindowListener(listen);


                frame.setVisible(true);
            }

        };
        SwingUtilities.invokeLater(r);
    }

}

I had the opengl display attach to the JFrame before i did the runnable. But after adding the runnable the display now shows up the same size as my screen size. I have tried rearranging the

canvas.setSize();

and the

frame.setSize();

but nothing changes the opengl display is still the same size and when i try to close the JFrame first rather then close the display first i get this error:

Exception in thread "AWT-EventQueue-0" java.lang.IllegalStateException: From thread Thread[AWT-EventQueue-0,6,main]: Thread[main,5,main] already has the context current

which points me to my

Display.destroy();

which im guessing is telling me that i am not properly disposing the display? Can anyone help me attach the opengl display to the JFrame and fix the error above?

Answer 1

It appears that you started the Display in the "main" thread (which gives the main thread the current OpenGL context), but you're trying to destroy the display from a different thread, which in this case is the Event Dispatch Thread (EDT). However, only one thread can have the current OpenGL context at a given time.

Although it is possible to change which thread has the current context, I don't think that's what you want to do here.

What we want to do here then is to destroy the display on the same thread that we created it on (the thread with the current OpenGL context). An approach I've seen is to use the Canvas's addNotify() and removeNotify() methods, which are run on the EDT, to set a flag that is checked on the OpenGL thread to determine when to destroy the display.

Also, the question mentioned problems about setting the size of the display. Your JFrame display size and Display size were not being set to what you desired because of how setSize() and LayoutManager's work. Please see the Java tutorials and documentation for details. In the following example, I have use one approach to address this issue.

So here is an example trying to stay close to the intent of the code posted in the question:

import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

import org.lwjgl.LWJGLException;
import org.lwjgl.opengl.Display;
import org.lwjgl.opengl.DisplayMode;

public class LWJGLTester {

    private volatile boolean isRunning = false;

    /*
     * The question asker seemed to desire that the JFrame be 800x600 and
     * that the Display be 300x300.  Regardless of the desired sizes,
     * I think the important thing is to set the Canvas and Display to the same sizes.
     */
    private int frameWidth = 800;
    private int frameHeight = 600;
    private int displayWidth = 300;
    private int displayHeight = 300;

    private Thread glThread;

    public static void main(String[] args) {
        new LWJGLTester().runTester();
    }

    private void runTester() {
        final JFrame frame = new JFrame("LWJGL in Swing");
        frame.setSize(frameWidth, frameHeight);
        frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent we){
                int result = JOptionPane.showConfirmDialog(frame, "Do you want to quit the Application?");
                if(result == JOptionPane.OK_OPTION){
                    frame.setVisible(false);
                    frame.dispose(); //canvas's removeNotify() will be called
                }
            }
        });

        JPanel mainPanel = new JPanel(new BorderLayout());

        JButton button = new JButton("BUTTON");
        JPanel buttonPanel = new JPanel();
        buttonPanel.add(button);
        mainPanel.add(buttonPanel, BorderLayout.NORTH);

        Canvas canvas = new Canvas() {
            @Override
            public void addNotify() {
                super.addNotify();
                startGL();
            }

            @Override
            public void removeNotify() {
                stopGL();
                super.removeNotify();
            }
        };
        canvas.setPreferredSize(new Dimension(displayWidth, displayHeight));
        canvas.setIgnoreRepaint(true);

        try {
            Display.setParent(canvas);
        } catch (LWJGLException e) {
            //handle exception
            e.printStackTrace();
        }
        JPanel canvasPanel = new JPanel();
        canvasPanel.add(canvas);
        mainPanel.add(canvasPanel, BorderLayout.SOUTH);

        frame.getContentPane().add(mainPanel);

        //frame.pack();
        frame.setVisible(true);
    }

    private void startGL() {
        glThread = new Thread(new Runnable() {
            @Override
            public void run() {
                isRunning = true;
                try {
                    Display.setDisplayMode(new DisplayMode(displayWidth, displayHeight));
                    Display.create();
                } catch (LWJGLException e) {
                    //handle exception
                    e.printStackTrace();
                }

                // init OpenGL here

                while(isRunning) {
                    // render OpenGL here
                    Display.update();
                }

                Display.destroy();
            }
        }, "LWJGL Thread");

        glThread.start();
    }

    private void stopGL() {
        isRunning = false;
        try {
            glThread.join();
        } catch (InterruptedException e) {
            //handle exception
            e.printStackTrace();
        }
    }

}

Note: This is example was tested using lwjgl version 2.9.1, since that seemed to be the latest version available at the time the question was originally posted.