problem, be it adding a square bitmap mask to a layer or adding more
content to the layer that you’re rotating. You could also draw a square on
another layer and rotate both at once.
As long as the dimensions for the layer or layers are even-by-even or odd-
by-odd, it’ll be fine.
An Easier Fix
Changing the origin of rotation to the top left (or any other corner) will
ensure it is on a pixel boundary, guaranteeing perfect results every time. To
do this, click on a corner origin after selecting the Free Transform tool, but
before rotating. This works brilliantly and is the simplest solution yet.