QML/Qt (C++) Rotation using quaternion with beginNativePainting()

[Mac91]

Hi

I’ve got a quaternion and I need to apply it in QML/Qt to rotate an object to align with the original rotated object. 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.y*q.z + q.w*q.x), q.w*q.w - q.x*q.x -q.y*q.y +q.z*q.z);
}

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

public static double getRoll(Quat4d q)
{
return Math.atan2(2*(q.x*q.y + q.w*q.z), q.w*q.w +q.x*q.x - q.y*q.y - q.z*q.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 data 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 4×4 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 QMatrix4×4, 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?