Thank you very much for your answer!
I must use QGraphicsProxyWidget because i need to flip the application of 180°! I'm in an embedded system with petalinux where i can't use a window system like x11 and so the rotation has to take place at a higher level (in the qt code)...
The previous code with the if statement works quite well...sometimes it doesn't receive the multitouch but it's decent! I just don't understand why if i pass the TouchBegin to QGraphicsVIew::viewportEvent(event) no TouchUpdate arrives...instead if i return true TouchUpdate and End arrive...