Facebook may be the world's most powerful app, but it's still just an app on Apple's operating system.

Facebook's grand vision for augmented reality was that it would make it easy for any developer to build and distribute an AR experience -- as long as it lived inside Facebook's app. But Apple has once again used its control of the mobile operating system to build a wider platform than Facebook can, this time with AR that lives inside developers' own apps.

This already played out with mobile apps.

On the open web of desktops, Facebook built a massively powerful game platform that spawned huge businesses like Zynga. On mobile, it couldn't do the same. Apple forbid developers from building app stores inside their apps. Facebook tried to build its own HTML5 game platform inside its native app anyway.

Here comes the augmented reality platform war

Yet since HTML5 web games couldn't draw on the phone's computing power the same way as a native app, Facebook's "Project Spartan" flopped while the Apple App Store thrived. Facebook promised virality to these app developers, but since their experiences would be buried layers deep inside the phone's homescreen, then the distracting Facebook app, and then inside its HTML5 app platform alongside competitors, they never flocked aboard.

Now Facebook is in danger of that same scenario playing out with augmented reality.

Facebook knows that sleek, capable, affordable AR glasses are still years away. Instead, it sees that phone camera as today's AR device, which already has massive scale. So at this year's F8 in April, it launched the Facebook Camera Effects platform. Developers can use its AR Studio program to develop interactive AR experiences that overlay make-believe animation atop the real world, triggered by locations, objects, data streams, and more.

Facebook has a number of advantages with this strategy. Its app is already massively popular, with 1.9 billion monthly users. It has 10-year history of working with developers. And since everything in AR happens "on camera" it will be easy for users to share the content with friends via Facebook, helping the developers to grow.

But as desktop games, brand Pages, and news publishers have learned, depending entirely on Facebook's walled garden can be risky. If Facebook changes directions, seeks to shield its users from noise, or wants to assume more power, there's little these outsiders can do to control the terms of the deal. Suddenly they can see their viral reach decimated, because since Facebook hosts all these developers, poor experiences reflect on it directly so it's quick to prioritize long-term user satisfaction over everyone else's businesses.