[OLD]QML/Qt (C++) Rotation using quaternion

Maciej Smith

Hello
I've got a quaternion and I need to apply it in QML/Qt. What I have tried so far:

for the reference: @quaternion = {0.826351,-0.405726,-0.353097,0.166890}@

and I get Yaw, Pitch, Roll with (java):

   @ public static double getPitch(Quat4d q)

{
return Math.atan2(2*(q.yq.z + q.wq.x), q.wq.w - q.xq.x -q.yq.y +q.zq.z);
}

public static double getYaw(Quat4d q)
{
return Math.asin(-2*(q.xq.z - q.wq.y));
}

public static double getRoll(Quat4d q)
{
return Math.atan2(2*(q.xq.y + q.wq.z), q.wq.w +q.xq.x - q.yq.y - q.zq.z);
}@

So I try QML:

@Item {
id: rectangle1
width: 300
height: 300
scale: 1
anchors.centerIn:parent;

    property double angleX: -61.87454134010583
    property double angleY: -26.624468050434572
    property double angleZ: 38.97955600504172
    property int originX: width/2
    property int originY: height/2

    }
    transform: Rotation {
        origin.x: rectangle1.originX;
        origin.y: rectangle1.originY;
        axis { x: 0; y: 0; z: -1 }
        angle: rectangle1.angleZ }

    Item {
          id: rectangle2
          width: 300
          height: 300
          scale: 1
          anchors.centerIn:parent;

          transform: Rotation {
              origin.x: rectangle1.originX;
              origin.y: rectangle1.originY;
              axis { x: 0; y: -1; z: 0 }
              angle: rectangle1.angleY }

          Rectangle {
                id: rectangle3
                width: 300
                height: 300
                color: "#ffffff"
                scale: 1
                opacity: 0.70
                anchors.centerIn:parent;

                focus: true

                transform: Rotation {
                    origin.x: rectangle1.originX;
                    origin.y: rectangle1.originY;
                    axis { x: -1; y: 0; z: 0 }
                    angle: rectangle1.angleX }
          }
    }
}@

I used 2 Items and 1 Rectangle to get the rotation right on the canvases, but the sata doesn't seem to fit.
So I thought maybe I just don't know jack about Quaternions and I'm getting the wrong data out of it, so I have tried Qt and here I am right now - I found the beginNativePainting() in QPainter, but I don't fully understand it, and the example in the documentation doesn't even work.

So I have a transformation matrix that is 4x4 from OpenGL and I try:

@void Dialog::paintEvent(QPaintEvent *e)
{
QPainter painter(this);
painter.fillRect(50,50,100,100,Qt::red);
painter.beginNativePainting();

double modelview_matrix[16]= {-0.874483, 1.527267, -2.199979, -0.760204, -0.576585, -0.299399, 0.000000, -0.078945, -0.375442, 0.923478, 0.000000, 0.644870, -0.725668, -0.239894, 0.000000, -0.095929};

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glLoadMatrixd(modelview_matrix);

glColor3f(1,0.4,0.4);
glPushMatrix();
glPopMatrix();

painter.endNativePainting();

}@

And I tried using the quaternion itself (which is very desired, small data etc.)

@void Dialog::paintEvent(QPaintEvent *e)
{
QPainter painter(this);
painter.fillRect(50,50,100,100,Qt::red);
painter.beginNativePainting();

QMatrix4x4 mat;
mat.setToIdentity();
const QQuaternion *q = new QQuaternion(0.826351,-0.405726,-0.353097,0.166890);
mat.rotate(q->normalized());

painter.endNativePainting();

}@

So I guess my question would be how does the QPainter::beginNativePainting() work, how do I make it work, because as I said even the example from http://harmattan-dev.nokia.com/docs/library/html/qt4/qpainter.html#beginNativePainting doesn't seem to work, and in my case nothing happens in both examples. Do I have to draw something inside the begin - end native painting and it takes an effect on that or should it work with the
@painter.fillRect(50,50,100,100,Qt::red);@

declared earlier?

Another question I have is about the QMatrix4x4, I don't fully understand how it Identifies itself with setToIdentity, what does it identify itself with in my example even? Does it identify itself with the QPainter object?