Function GridGraphUpdatePromise.CalculateRectangles

void CalculateRectangles (

GridGraph	graph	The graph
IntRect	rect	The rectangle to update. Anything inside this rectangle may have changed (which may affect nodes outside this rectangle as well).
outIntRect	originalRect	The original rectangle passed to the update method, clamped to the grid.
outIntRect	fullRecalculationRect	The rectangle of nodes which will be recalculated from scratch.
outIntRect	writeMaskRect	The rectangle of nodes which will have their results written back to the graph.
outIntRect	readRect	The rectangle of nodes which we need to read from in order to recalculate all nodes in writeMaskRect correctly.

)

Calculates the rectangles used for different purposes during a graph update.