I am trying to make a storyboard for my button with Expression Blend. I would like it to move, and then to disapear behind some virtual panel. I think I could do it by defining an "area of visibility" for my button, so when it moves out of that area, it is hidden. Is it possible ? Thanks for your help.
It sounds like you want your button to disappear as it were sliding into an invisible slot in your GUI. If that's the case, your solution will deal with animating a clipping region to make it progressively bigger until it covers your button. I'm almost certain this needs to be in code and not XAML though. At the end of the animation you can simply set the visibility to hidden/collapsed and then remove the clipping region entirely.