Added to formspec backgrounds:
background[pos_x,pos_y;size_x,size_y;background_image]
When backgrounds are used in formspec no item slot rectangles are drawn.
- You have 2 stacks: a with x items and b with y<x items
- Take a with your mouse and place it on b
- Whole stack a moves to b
- (y * 2 - x) items move from b to a
- (x - y) items are left to the mouse cursor