Have you tried just to write a computer program to find the exceptional values? They are indeed, finitely many; as soon as the region contains a unit square in every direction (for which it is enough to contain a disk of diameter $\sqrt 2$), it has an integer point in it regardless of the orientation, so for all $b$ with $|b|>15$, say, all $4$ possibilities are realized and (taking symmetries into account), you need to check just about $100$ values, which should be a piece of cake. — fedja 22 hours ago
I am pretty lame in drawing pictures - MetaPost is basically the only thing I am familiar with well enough to create some reasonable picture.
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