requires: {#LinkedCollection. #Region}.
provides: {#QuadTree}.

collections addPrototype: #QuadTree derivedFrom: {LinkedCollection}.
"A QuadTree is a Tree structure designed for graphics comparisons, or at least
2-d region sorting."
QuadTree addSlot: #treeParent.
QuadTree addSlot: #bounds.
"The Rectangle Region that corresponds to this node."

collections addPrototype: #QuadTreeNode derivedFrom: {QuadTree}.
"Each node has 4 sub-nodes, separated vertically and horizontally at one
Point."
QuadTree addSlot: #c1.
QuadTree addSlot: #c2.
QuadTree addSlot: #c3.
QuadTree addSlot: #c4.

collections addPrototype: #QuadTreeLeaf derivedFrom: {QuadTree}.
"The leaves can reference Regions which they contain but which are not part of
the QuadTree."
QuadTree addSlot: #contents valued: ExtensibleArray newEmpty.