Sometimes puzzle pieces disappear of my screen when I drag and drop a puzzle piece on another, especially one (see the two screenshots)
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This would be rather difficult to change, and I don't know if this should even be fixed. The pieces are items, so when placed on top of each other, the piece underneath is covered by the top one.
Yes i understand but to someone don't know this, he would be surprised that a piece disappear.
Personnaly because of this bug, i failed 5-10 times the quest before i know this..
Drop a piece on top of another, and you have failed the task anyway as you then won't have enough moves left :-P
Seriously, though, it would be possible to make what happens more obvious if two things are implemented:
1. Make stackable items merge stacks automatically when on the ground. Personally I'd like that to happen, but there may be some downsides. I'd like to hear opinions on that.
2. Make the puzzle tokens stackable, so that given 1 is implemented tokens dropped on top of each other would show the item number, which should be a rather good indication that the tokens are occupying the same location, rather than disappeared. The downside is that the player grabbing the token stack would be moving by default the entire stack rather than just one token. That is probably not a major issue, because as already stated, it is not possible to complete the puzzle at that stage anyway.
(On a tangentially related note, we need to teach players about splitting stacks. Maybe the first time the player moves a stack would be the right time for the tutorial event. Should probably exclude grabbing anything to bag, as that's often done with a click rather than a drag, nor is splitting particularly often desired when just picking up items).