Facebook just made a surprising move that could save its one shrinking business

Facebook's quarterly earnings reports have long been rosy affairs for the company and its shareholders as it continues to swell its user numbers, revenue, and profits.

But there's one category where Facebook has been trending downward: Revenue from payments and fees.

Facebook even warned on last year's 10Q report that investors should expect that number to continue to decline.

Why? Because its payments revenues come from people playing Facebook games on their laptop or desktop computers. These days most people are using Facebook on their smartphones (where games typically have their own apps), so Facebook isn't reeling in as much cash.

Although payments revenue hasn't declined sequentially every quarter, it's down 23% since Q4 2014. Back in 2011, Facebook made about 12% of its total revenue from people addicted to Zynga's popular Facebook games like Farmville and Cityville. Today, only about 3% of its revenue came from Facebook games.

But Facebook could be about to reverse that trend.

This week, the company announced an "all-new PC gaming platform" in partnership with game engine Unity that will be a standalone application.

Details so far are sparse and Facebook has a formidable opponent in Steam, a gaming platform that the concept seems to rival. It would likely take a pretty serious investment for Facebook to win over video-game crowds. But if the company manages to release a platform that people actually use, it could start juicing its payments revenues back up as people buy games or make gaming purchases on their laptop and desktop computers through Facebook again.

Here's a look at how much the global games market is set to swell on personal computers: