coordinates and point on click

hello.

I have create a system that draws little circles or points in opengl 3 where I click the mouse in a qt opengl widget.

The problem are the coordinates: the circle is not drawed in the position of the mouse when i click.

I divide the point x for the width and the point y for the height for and I have a point from 0 to 1

But how i can trasform these points from 0 to 1 to the opengl coordinates?

i must use the opengl viewport?

or the ortho matrix?

how?

ps.

the glwidget is on a mdi window

thanks.