Visits each node in the quadtree in pre-order traversal, invoking the specified callback with arguments
node, x0, y0, x1, y1 for each node, where node is the node being visited, ⟨x0, y0⟩ are the lower bounds of the
node, and ⟨x1, y1⟩ are the upper bounds.
(Assuming that positive x is right and positive y is down, as is typically the case in Canvas and SVG,
⟨x0, y0⟩ is the top-left corner and ⟨x1, y1⟩ is the lower-right corner; however, the coordinate system is arbitrary,
so more formally x0 <= x1 and y0 <= y1).
Visits each node in the quadtree in post-order traversal, invoking the specified callback with arguments
node, x0, y0, x1, y1 for each node, where node is the node being visited, ⟨x0, y0⟩ are the lower bounds of the node,
and ⟨x1, y1⟩ are the upper bounds.
(Assuming that positive x is right and positive y is down, as is typically the case in Canvas and SVG, ⟨x0, y0⟩
is the top-left corner and ⟨x1, y1⟩ is the lower-right corner; however, the coordinate system is arbitrary,
so more formally x0 <= x1 and y0 <= y1.) Returns root.