[SOLVED] Inventory item dragging: how do I track a GUI's location in a certain space?

I want to create an inventory item dragging system but to do that I first must make it draggable. I would have the player hold their mouse button and the GUI image is stuck to the mouse cursor until the client lets go of it.

Now for the problem I described in the title, I want to detect where it's located so that if I drag the item to an empty item slot, the script knows which slot it should be placed in. If I drag it to a hotbar slot, the script will know where to place so item in that slot while emptying its prior slot it was dragged from.

I however have no clue how to do something like that and the closest thing I know to such is Region3 but there may be more efficient ideas than comparing it to Region3 but with GUIs.