Was most complicated in my head was I thinking.
I was using many layers : one background, one shadow, but only one layer suffice : Background, put Shadow on it, Z Layer top. I use Source atop because I need some FX on Shadow.
It's work, thank you !
Maybe a question about Canvas : how to create object on it? I create object on a Layer, fine, then use Paste object, but they are already in Layer, I need to remove manually? Don't get the point…