I'm talking about those Invention Assignment clauses in employment contracts (especially with regards to California labor code section 2870)
"Prohibiting employee assignment to an employer of inventions that the employee developed entirely on his or her own time without using the employer's equipment, supplies, facilities, or trade secret information, except for those inventions that either: (a) relate at the time of conception or reduction to practice of the invention to the employer's business, or actual or demonstrably anticipated research or development of the employer; or (b) result from any work performed by the employee for the employer."
Suppose the company makes windows software using C++ that specifically targets financial institutions in providing them financial data...and then a Windows C++ programmer that works for this company make a Windows minesweeper software using C++ purely using his own equipment and solely on his own time, will that be considered "related" to the company's business simply because it's also a windows software and is also written in C++ (ie. despite the fact that the program itself (minesweeper) is completely irrelevant to making financial software that provides data to financial institutions)? Ie. if that scenario occurs, will the company then have ownership of the minesweeper program source code?
Note that a company can sue you or come after you whether you are in breach or not. They can make in painful and expensive if they want to, and I'm not a lawyer.
Programming languages do not correlate to any practice, or specific knowledge from an employer. Companies around the world use many different languages and your employers competitors also probably use it so it's not really part of any strategic advantage. If they have custom libraries or frameworks that the employer created and you use those in your work that would be an issue. But since you are making a GAME and your employer works in banking / financials that would be a pretty clear separation. If you were making a game based on an idea you got at work about a fun way to categorize expenses or organize finances then that 'may' be crossing the line. But even then, that's not your employers line of business and they are not in the business nor are you in the business at their place of employment to make games.