This a second version of my book-placer macro, useful to fill shelves with rows of books.
It was originaly designed for Megapov (for my IRTC entry “alchlab”), but it works withouth modification with 3.5. In this version I fine tuned the behavior for better placement. The trick consists on using the “trace()” function to let the books fall until they reach the prior book. This is combined with some random probabilities for different factors.