I found this function ... i could have found it by myself. Thanks for the time i saved.
I still have 1 questions regarding the use of mask :
How should i used the "levels" value ?
I tried to not mask the red part of this symbol (see attached image). The red part of the symblol is the "Layer" 2 is the symbol. My map Layer is rendered with symbol having 1, 2 or 3 symbol Layers.
when i try set use a value (i tried from A to 18), i get no results and when i re-open the "advanced drawing option ..." window, the "Enable to associate levels to masked layers" option is no longuer selected
When this issue will be solved i would have only on thing to manage : mask management in letters with holes such as "O", "D" ...
Thanks again for your help.
Guillaume