Question

Given this simple example that I got from the JOGAMP wiki, why would the mouse coordinates be off by 40 in the y-direction and 20 in the x-direction? Clicking on the bottom right corner of the screen shows the coordinates (620, 440) and not (640, 480) like I would expect.

Thanks for the help!

Here’s the program:

import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.awt.GLCanvas;
import javax.swing.JFrame;

import java.awt.BorderLayout;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

/**
 * A minimal program that draws with JOGL in a Swing JFrame using the AWT GLCanvas.
 *
 * @author Wade Walker
 */
public class OneTriangleSwingGLCanvas implements MouseListener{

    static {
        // setting this true causes window events not to get sent on Linux if you run from inside Eclipse
        GLProfile.initSingleton( false );
    }

    public static void main( String [] args ) {
        GLProfile glprofile = GLProfile.getDefault();
        GLCapabilities glcapabilities = new GLCapabilities( glprofile );
        final GLCanvas glcanvas = new GLCanvas( glcapabilities );

        OneTriangleSwingGLCanvas mouse = new OneTriangleSwingGLCanvas(); 
        glcanvas.addMouseListener(mouse); 

        glcanvas.addGLEventListener( new GLEventListener() {

            @Override
            public void reshape( GLAutoDrawable glautodrawable, int x, int y, int width, int height ) {
                OneTriangle.setup( glautodrawable.getGL().getGL2(), width, height );
            }

            @Override
            public void init( GLAutoDrawable glautodrawable ) {
            }

            @Override
            public void dispose( GLAutoDrawable glautodrawable ) {
            }

            @Override
            public void display( GLAutoDrawable glautodrawable ) {
                OneTriangle.render( glautodrawable.getGL().getGL2(), glautodrawable.getWidth(), glautodrawable.getHeight() );
            }
        });

        final JFrame jframe = new JFrame( "One Triangle Swing GLCanvas" ); 
        jframe.addWindowListener( new WindowAdapter() {
            public void windowClosing( WindowEvent windowevent ) {
                jframe.dispose();
                System.exit( 0 );
            }
        });

        jframe.getContentPane().add( glcanvas, BorderLayout.CENTER );
        jframe.setSize( 640, 480 );
        jframe.setVisible( true );
    }

    @Override
    public void mouseClicked(MouseEvent e) {
        // TODO Auto-generated method stub
        System.out.println("Mouse pressed at : (" + e.getX() + ", " + e.getY() + ")"); 
    }

    @Override
    public void mouseEntered(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseExited(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mousePressed(MouseEvent e) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseReleased(MouseEvent e) {
        // TODO Auto-generated method stub

    }
}

//OneTriangle.java

import javax.media.opengl.GL;
import javax.media.opengl.GL2;
import javax.media.opengl.glu.GLU;

public class OneTriangle {
    protected static void setup( GL2 gl2, int width, int height ) {
        gl2.glMatrixMode( GL2.GL_PROJECTION );
        gl2.glLoadIdentity();

        // coordinate system origin at lower left with width and height same as the window
        GLU glu = new GLU();
        glu.gluOrtho2D( 0.0f, width, 0.0f, height );

        gl2.glMatrixMode( GL2.GL_MODELVIEW );
        gl2.glLoadIdentity();

        gl2.glViewport( 0, 0, width, height );
    }

    protected static void render( GL2 gl2, int width, int height ) {
        gl2.glClear( GL.GL_COLOR_BUFFER_BIT );

        // draw a triangle filling the window
        gl2.glLoadIdentity();
        gl2.glBegin( GL.GL_TRIANGLES );
        gl2.glColor3f( 1, 0, 0 );
        gl2.glVertex2f( 0, 0 );
        gl2.glColor3f( 0, 1, 0 );
        gl2.glVertex2f( width, 0 );
        gl2.glColor3f( 0, 0, 1 );
        gl2.glVertex2f( width / 2, height );
        gl2.glEnd();
    }
}

Answer 1

The statement jframe.setSize(640, 480) specifies the size of the entire frame, including any decorations such as drag bar and border. You might examine the frame’s getInsets().

Also, GLCanvas is a heavyweight component. Rather than mixing, consider adding it to an AWT Frame.