So l tried successfully the trick with masking surfaces with bezier like you said and it was working very well, but l canted do everything l wanted :
l needed a central mapped surfaces with curves, and around this surface l wanted to uses several mapped surfaces, those with one single common extended source. This means l canted super pose a mask and the surfaces. Maybe it is hard to explain, maybe it is better to understand with this screencapture :
l had to mask the video around the eye (ok this could be improved on my side but l had no time for this)
l wanted the "jewels" using the same image source, l mean not using the same source on multiplied surfaces, but on background cutted by several mask, l mean using an undistorted source (like l often do).
but l canted because the surfaces of the eye are masking the jewels, and if l put the jewels on the first level/layer, the mask of the jewels would mask the eye..
That is why l also would like to use masks with beziers.
But l have to say on this project l had fun anyway
and the trick with the curved surfaces helped me a lot !! Thanks !