poombus You'll need to implement a simple drag and drop system. There are numerous ways to do it. Here's one.
Have a top level script that at all times tracks which dice icon is currently under the mouse. This can be done by receiving mouse_entered
end mouse_exited
signals from all visible dice icons. This script should also track global mouse button press/release events via _input()
callback.
When mouse is pressed, if there is a dice under the mouse, store it as a source for dragging operation and set internal state to dragging. When mouse is released, if the script is in dragging state and there is a dice under mouse, store it as a destination for dragging operation. At this point you know that drag has been performed and you know the source and the destination dice, so you can notify whomever is interested about it, either by emitting a custom signal or invoking an explicit callback. After the mouse has been released, set internal state back to not-dragging.