Trackball Implementation

Hello there!

I am trying to implement an arcball/trackball controller using Open GL and Qt. However, I am quite new to OpenGL. I am having a terrible, terrible, terrible time getting things to work.

I started by following this video: https://www.youtube.com/watch?v=3IQV65ApWGs

I am using Qt for my window, using their QtWidget class.

Basically, I have a cube around the origin. I want to orbit the camera around the cube with the mouse. Right now, when I drag the camera seems to go NUTS. Goes to random positions.

I hope you guys can help. I feel like I’ve tried nearly everything here.

First my mouse handling:


void GLWidget::wheelEvent(QWheelEvent *e){
    scrollDelta +=  e->delta() / 120;
}

void GLWidget::mousePressEvent(QMouseEvent *e){
    rotate=false;
    if(e->button() == Qt::LeftButton){
        //oldX = e->x(); // Set this to the mouse position
        //oldY = e->y(); // Set this to the mouse position

        //newX = e->x();
        //newY = e->y();

        qDebug() << oldX << oldY << newX << newY;

        rotate = true;

        useArcBall = true;
     }
}

void GLWidget::mouseMoveEvent(QMouseEvent *e){
    if(e->buttons() & Qt::LeftButton){
        //qDebug() << QString::number(e->x());
        if(rotate){
            newX = e->x();
            newY = e->y();
            updateMouse();

        }
        //oldX = e->x();
        //oldY = e->y();
    }

}

void GLWidget::mouseReleaseEvent(QMouseEvent *e){
    if(e->button() == Qt::LeftButton)
        useArcBall = false;

}

void GLWidget::updateMouse()
{

        QVector3D v = getArcBallVector(oldX,oldY); // from the mouse
        QVector3D u = getArcBallVector(newX, newY);

        float angle = std::acos(std::min(1.0f, QVector3D::dotProduct(u,v)));

        QVector3D rotAxis = QVector3D::crossProduct(v,u);

        QMatrix4x4 eye2ObjSpaceMat = rotationMat.inverted();

        QVector3D objSpaceRotAxis = eye2ObjSpaceMat * rotAxis;

        qDebug() << 4 * qRadiansToDegrees(angle);


        //modelview.rotate(4 * qRadiansToDegrees(angle), rotAxis);

        //oldRot = newRot;

        //oldX = newX;
        //oldY = newY;

        //qDebug() << objSpaceRotAxis.normalized();


    if(true){
    rotationMat.rotate(4 * qRadiansToDegrees(angle), objSpaceRotAxis);
    }

}


Now the arcball related math:


QVector3D GLWidget::getArcBallVector(int x, int y)
{
   QVector3D pt = QVector3D(2.0 * x / GLWidget::width() - 1.0, 2.0 * y / GLWidget::height() - 1.0 , 0);
   pt.setY(pt.y() * -1);

   // compute z-coordinates

   float xySquared = pt.x() * pt.x() + pt.y() * pt.y();

   if(xySquared <= 1.0)
       pt.setZ(std::sqrt(1.0 - xySquared));
   else
       pt.normalize();

   return pt;

}

And this is the part where I render everything:


void GLWidget::paintGL()
{
    QMatrix4x4 modelview;

    QPainter painter;
    painter.begin(this);

    painter.beginNativePainting();

    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glFrontFace(GL_CW);
    glCullFace(GL_FRONT);
    glEnable(GL_CULL_FACE);
    glEnable(GL_DEPTH_TEST);

    // Matrix has to be UPDATED, and not every frame! That's the issue.

    //modelview.translate(0.0f, 0.0f, 1.0f);

    //modelview.rotate(m_fAngle, 1.0f, 0.0f, 0.0f);
    //modelview.rotate(0.1f, 0.0f, 0.0f, 1.0f);
    //modelview.scale(m_fScale);
    float radius;
    radius = 200;

    float focus;
    focus = 0;

    float eyeX = focus + radius*cos(phi)*sin(theta);
    float eyeY = focus + radius*sin(phi)*sin(theta);
    float eyeZ = focus + radius*cos(theta);

     modelview.perspective(90.0f, 4.0f / 3.0f, 0.1f, 3000.0f);

     //if(lookatint < 0)
    // {
      //QVector3D lookAt = QVector3D(eyeX, eyeY, eyeZ + scrollDelta);

    modelview.lookAt(QVector3D(eyeX,eyeY,eyeZ), QVector3D(0,0,0), QVector3D(0,1,0));
     //lookatbool = false;
     // lookatint++;
     //}

    // New Trackball code

    modelview = rotationMat * modelview;

    modelview.scale(1 - scrollDelta / 10);