trackball widget and infinite movement

Hi,
I need to know if it's possible to grab the mouse pointer on the mousePressEvent, hide it, and continue to report mouseMoveEvents with no restriction of distance. I would like to design a trackball widget: once clicked, the only information that matters is the dx and the dy from the initial position. I don't want the edges of the screen to interfere with it. On the release event, the mouse pointer should be at the initial position. Otherwise, is it possible to wrap around the edges of the screen? I'm writing a program and I' moving objects in Opengl views. Sometimes, it doesn't make sense to be stopped by the edge of the screen.

Antoine