I've used Pic.Width because in this puzzle, the viewport includes at least from 0,0 to (Pic.Width,Pic.Height). Make sure you use values that put your pieces inside the viewport, so the user can see all pieces.
Detecting Player Win
One important thing you should do is detect player win. Since we are adding all "joined" pieces to a group, the player wins when all pieces are in the same group.
To make a simple winning detection routine, go to the blank event with action "Set MyGroup to ActualPiece.Group". Create a new event there with two conditions:
System.Pick All ActualPiece
System.Compare ActualPiece.PickedCount = LogicalH*LogicalW
Add this action:
Flash 0.30 seconds on, 0.50 seconds off, 0.50 seconds on, duration 10 seconds.
Finally, collapse the event under it so you can change event order and check for puzzle completion straight after we join pieces. This means the event with the "For..." should be on top of this one:
-->(subevent 1) Pick all ActualPiece / For each ActualPiece / ActualPiece Group=MyGroup
-->(subevent 2) Pick all ActualPiece / ActualPiece.Group=Mygroup / ActualPiece.PickedCount=LogicalH*LogicalW
If you play the puzzle and complete it, it should flash for 10 seconds!
I strongly suggest you to make your own customized "Winning" routine. Keep in mind this: flashing produces strange neuronal activity and can cause side effects such as epilpsy.
The project at this point is attached to this tutorial, in the "tutorial_puzzle_final.capx" file.