Question: I am using QT to develop a rich UI application. 

1. I need to position widgets at absolute positions
2. I should be able to put the widget in background / foreground to add a few effects.

Simple example would be, I have to show a boiler with the water level inside the feed tank. 

1. Take a feed tank image and embed in a label.
2. Position a progress bar in the center of the feedtank to display water level.

Now in this case the progress bar would be in the foreground and the label in the background. 

Regards,

Answer: 
You just need to create your widget, indicate its parent QWidget and then display it.

Don't add it to the parent layout else you will not be able to move it as you want.

Don't forget to indicate its parent else it will be displayed as independent widget.

In these conditions your widget will be considered as child of the QWidget but not member of the parent's layout. So it will be a "floating" child and you must manage it's behavior when resizing parent's QWidget.
I do it by creating a class based on Qwidget put its position in the constructor

ex:
QPointer a = new QWidget (0, posx, posy, width, height)

in the constructor of this Qwidgetclass add these integrers posx, posy, width, height and then do
this.move(posx,posy);
this.resize(width,height);