As discussed on GitHub, it would be useful if Box2I and Box2D had methods for creating boxes centered on a particular (fractional) point.

Given that the Box* classes cannot afford more constructors, and we still don't have a good way to discover functions, this capability is best implemented as static factory methods:

Box2I Box2I::makeCenteredBox(Point2D const& center, Box2I::Extent const& size);

Box2D Box2D::makeCenteredBox(Point2D const& center, Box2D::Extent const& size);

I do not plan to add a Box2I::makeCenteredBox(Point2I, Extent) method: I'm worried that it might lead to confusion with (Point2D, Extent), and as Jim Bosch pointed out it's not clear what the best behavior is for even-sized boxes.

The desired functionality is already present in the implementation for Exposure::getCutout, so this work is just a matter of factoring the code, writing new unit tests, and being very careful about the distinctions between Box2I and Box2D.