Convert 3d point into screen coordinate

Hi,

I am using OCCT 7.1 and Qt5.6.

I would like to display a Widget at a specific coordinate (2d). I use a QtWidget that a i move with 2d coordinate.

The position of the widget is computed from the position of an AIS_InteractiveObject displayed in the view. So i have to convert the 3d position of the interactive object into 2d screen coordinate. It's like making a projection of the 3d object from world coordinate to screen coordinate.

I found in occ sources this code 

gp_Pnt point3d;

Handle(V3d_View) myV3dView =  ...;
double Xv,Yv;
myV3dView->Project(point3d​.X(),point3d​.Y(),point3d​.Z(),Xv,Yv);
Standard_Integer p2dX p2dY;
myV3dView->Convert(Xv,Yv, p2dX,p2dY);

I think this code convert a 3d world coordinate into screen coordinate. I search on the internet and this solution seems to be ok. But my result is not ok.

Asume that the AIS_InteractiveObject is the representation of a point.

If the AIS_InteractiveObject 3d position is visible in the view, i think i can get the projected 2d screen coordinate of this position.

The 2d point must be :

0 < pnt2dX < viewWidth

0 < pnt2dY < viewHeigth​​

I dont get good result. For the same 3d position, if i change the zoomFactor (myView->SetZoom(...) ), i dont get the same 2d position.

What am i doing wrong ? Can you help me ?

Regards