Here is the same question with a working example
https://codereview.stackexchange.com/questions/274781/qt-creating-a-dark-overlay-to-apply-on-top-of-other-widgets-with-animation

Use,

animation->stop()

OK. I changed the code to make sure there is nothing else consuming CPU power while moving. Still, specially when moving fast, edges are jagged while moving and sometimes it even jumps.

Could be the limit of the ARM CPU or the directFB graphic acceleration.
It would be better if supplying new coordinates to the FB would be synced to the frame rate, but I don't think that I can change something on that level.

Too bad ..

You still first need to move your widget and only then can you put it in your QStackedWidget's layout.

The first one: both button and animation are local stack variables and get destroyed at the end of the function, before anything starts to animate. Don't do that.

The second one: if this points to a top level widget then its parent is most probably null. You can't animate a property of non-existing object. Make sure the first parameter points to a valid object. Also make sure you either delete the animation object somewhere or give it a parent (3rd parameter) or else you're leaking memory.

Third one: you created two animations without any values i.e. it doesn't know how to animate the "geometry" property. Before you start the group add to your animations some duration, start and end values like in your previous examples. Also, again, make sure you delete the animations and the group or give them a parent or you're leaking memory.

p.s. This forum no longer uses @ for code blocks. To properly format code just indent it either 4 spaces or a tab. I edited your post to fix this.