Question

I’m trying to implement a basic physics engine in Java and I’m using the JOGL bindings so I can visualize the results. I can create and rotate shapes easily enough, but have run into problems whilst manipulating the viewport and whilst moving the shapes.

I don’t think a clipping issue – I’ve tried using the gluPerspective method with a massive range (0.0001f – 10000f) with no success. When I move the camera further away from my objects or move the objects themselves, they disappear.

Tutorials about JOGL are few and far between and many also use different versions of OpenGL, so I turn to the only friend I have left: the wonderful users of stack overflow. 🙂

Flattery aside, the code follows:

public class JoglEventListener implements GLEventListener, KeyListener, MouseListener, MouseMotionListener {
// keep pointer to associated canvas so we can refresh the screen (equivalent to glutPostRedisplay())     
public GLCanvas canvas;
public Particle triforce;
public float x;

// constructor
public JoglEventListener(GLCanvas canvas) {
    this.canvas = canvas;
}

@Override
public void display(GLAutoDrawable drawable) {
    update();
    render(drawable);
}

@Override
public void init(GLAutoDrawable drawable) {
    triforce = new Particle();
    x = 0;
}

private void update() {
    triforce.integrate(0.0001);
    x = x + 0.25f;
}

 private void render(GLAutoDrawable drawable) {
    GL2 gl = drawable.getGL().getGL2();
    GLU glu = new GLU();

    gl.glClear(GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
    gl.glMatrixMode(GL2.GL_PROJECTION);        
    gl.glLoadIdentity();
    //gl.glFrustum (.5f, -.5f, -.5f * 1080, .5f * 960, 1.f, 500.f);
    glu.gluPerspective(0, 1, 0.1f, 100f);        


    gl.glMatrixMode(GL2.GL_MODELVIEW);
    gl.glLoadIdentity();
    gl.glHint(GL2.GL_CLIP_VOLUME_CLIPPING_HINT_EXT,GL2.GL_FASTEST);
    glu.gluLookAt(0, 0, 1.5, 0, 0, -10, 0, 1, 0);        
    //gl.glRotatef(90, 0f , 1f , 0f );
    //Draw some scale lines
    gl.glBegin(GL.GL_LINES);
    gl.glColor3f(0.75f, 0.75f, 0.75f);
    for (int i = 0; i < 20; i += 1)
    {
        gl.glVertex3f(-5.0f, 0.0f, i + 0.5f);
        gl.glVertex3f(5.0f, 0.0f, i + 0.5f);
    }
    gl.glEnd();

    //gl.glRotatef(x, 1f , 1f , 1f );         

    gl.glPushMatrix();
    gl.glTranslated(triforce.position.x, triforce.position.y, triforce.position.z);
    gl.glBegin(GL.GL_TRIANGLE_STRIP);                       
    gl.glColor3f(1f, 0f, 0f);                       
    gl.glVertex3d(0, 0, -2);
    gl.glColor3f(0f, 1f, 0f);                       
    gl.glVertex3d(0, 0.25d, -2);                
    gl.glColor3f(0f, 0f, 1f);                       
    gl.glVertex3d(0.25d, 0, -2);
    gl.glColor3f(1f, 1f, 0f);                       
    gl.glVertex3d(0.25d, 0.25d, -2.25d);
    gl.glEnd();                                       
    gl.glPopMatrix();

    gl.glFlush();
}

// (empty overridden methods omitted)

public Particle () {
    setMass(200d);
    velocity = new Vector3(0d, 30d, 40d);
    acceleration = new Vector3(0d, -20d, 0d);
    position = new Vector3(0d, 0d, 0d);
    damping = 0.99d;
}

public void integrate (double duration) {
    if (inverseMass <= 0.0d) {
        return;
    }
    assert (duration > 0.0);
    position.addScaledVector(velocity, duration);
    Vector3 resultingAcc = new Vector3(acceleration.x, acceleration.y, acceleration.z);
    velocity.addScaledVector(resultingAcc, duration);
    velocity.multEquals(Math.pow(damping, duration));
    //clearAccumulator();
}

public void setMass(double mass)
{
    assert(mass != 0);
    inverseMass = (1.0d)/mass;
}    

Before movement / starting position:

The shape drifts upward and is obscured from the right and top, becoming invisible:

Any help would be greatly appreciated! Thanks!

Answer 1

In the end, I was never able to track down the issue, and started again from scratch. I didn’t run into any further clipping issues on my new build.

My best guess as to my initial failure is an improperly used glHint or glClear call, or perhaps some problem with the version of JOGL I was referencing.