Xio, who developed the Tetris clone, argued that the mechanics behind it were essential to make a Tetris-like game.
However, the court decided that the idea of Tetris – which is not copyrightable – only extended to the concept of falling blocks being stacked together. Everything else, including the shapes of the blocks, was ruled to be the expression of the idea, which can be copyrighted.
The decision could have major implications across the board for game designers, as several studios either have court cases ongoing, or have publicly claimed their games were ripped off by other companies.
A full report on the case can be found here, and it’s worth reading for any developer concerned about plagiarism.