This week Valve hosted the Steam Developer Days in Seattle, where game creators got hands-on time with the Steam Machines and Valve's innovative new controller, while lectures covered topics as diverse as user-generated content, VR and game economies - as well as developing and coding for the Linux operating system and the OpenGL graphics API. This last element is crucial - not just for the success of the SteamOS and its accompanying hardware, but for the long-term expansion of Valve's gaming platform.

First, it's important to put the Steam Machines into context. The initial reveal at CES earlier this month didn't seem to impress too many gamers. The range of arguments pitched against the products revealed were many and varied: there were too many of them, they were over-priced, they were under-specced, they were ugly, there were few signs of the apparently necessary "consolification" of PC gaming beyond the already announced controller, and scant evidence of a "guiding force" from Valve in defining the new platform for the mainstream gamer.

In actual fact, what we are seeing here are the first fledgling steps of an entirely open gaming platform that will evolve into many different forms, with the living room console-style box just the first iteration of a post-Windows Steam system. It's not for Valve to decide what should or should not be a Steam Machine, it's up to the hardware manufacturers to do their best and let the market - the gamers - decide. Few, if any, of these machines will be commercially successful, but lessons will be learned and second-gen machines will be better, more powerful and inevitably cheaper. For its part, Valve has provided an operating system and the necessary controller, and as the agenda for the Steam Developer Days suggests, it's all about encouraging adoption of the Linux-based platform and the OpenGL graphics API.

But why? After all, the PC market as it is right now is clearly successful, and a massive majority of the computers shipped today have Windows pre-installed by default. The sudden leap in the capabilities of integrated graphics means that most modern computers can run just about any game you care to throw at them, even without a dedicated graphics card. There's an ecosystem in place that clearly works, so what is the point of moving game development to Linux and OpenGL?

"Divorcing Steam from Windows is the best chance Valve has in significantly growing its userbase, and the Steam Machines are just the first part of the plan."

This year's collection of Steam Machines have been dismissed as too expensive and ill-equipped to compete with Xbox One and PlayStation 4, but with the relentless improvements in PC tech, combined with the kind of ultra-aggressive price cuts we've seen on graphics tech recently, second or third-gen units could prove unstoppable.

From our perspective, the answer is remarkably straightforward: in the years to come, the PC and gaming markets will expand into places that Windows is ill-equipped to operate, and - crucially - where open platforms are already proven to dominate. In the short term, sticking with Windows is the safest bet for PC game developers but over the longer stretch, embracing open platforms - and the OpenGL graphics API in particular - makes better commercial sense.

Indeed, the demonstration of Nvidia's Tegra K1 chip at this year's CES was arguably more important for game developers than the reveal of the Steam Machines themselves. In essence, what we are looking at is an early preview of the radical expansion in gaming that Valve is laying the groundwork for right now. Tegra K1 is a remarkable product - a modern desktop graphics architecture (Kepler) downscaled into a mobile chip - offering more raw rendering power than Xbox 360 and PlayStation 3. Crucially, because it is desktop tech, it features compatibility with the exact same OpenGL API as its PC GeForce GPU siblings. That being the case, any existing Linux/OpenGL video game should be ripe for conversion onto the K1 platform - and all the other mobile graphics technologies that will follow.

Tegra K1 - the mobile GPU based on PC desktop tech We saw a compelling practical example of this in action during Nvidia's CES keynote. Frozenbyte's Trine 2 - which we recently covered in its PlayStation 4 incarnation - was shown running on a prototype K1 tablet. We checked in with the developer who confirmed a native 720p presentation, a 30fps target frame-rate and the same quality settings as the PS4/PC version. In essence, we are witnessing an Android port of a PC title offering an experience that similar to the last-gen console versions - if not slightly better. Yet this isn't a "mobile game" in the conventional sense. To all intents and purposes, this is the Linux/OpenGL game recompiled for another platform. Potentially, that's very exciting. "We're super excited about this too, basically the days of doing 'mobile ports' are over and that's good for us because we never really bothered with those - the compromises in graphics just weren't worth it," Frozenbyte's Joel Kinnunen told us. "We [would] rather work on something new (or at least on platforms that are exciting to us, like PS4 recently). Now with Tegra K1 we can easily add those devices to our platform possibilities. Android is a piece of work for sure but we seem to be getting the hang of that little by little." The demo is really impressive, but there are some frame-rate issues, and it's clear that Android itself needs to evolve to become more "game-friendly" to developers. At Nvidia's G-Sync reveal last November, we overheard John Carmack lamenting his inability to run certain code at 60Hz - not through any fault of his own but simply because of difficulties with the Android operating system. But on a larger scale, the arrival of K1 demonstrates that a convergence of some description between PC and mobile gaming is virtually inevitable. The parallels between Android and SteamOS are many: both use OpenGL as the graphics API of choice, both are open platforms, and as Frozenbyte has demonstrated with Tegra K1, the notion of mobile as a target for more technically ambitious PC-style games is now one step closer. "The arrival of K1 demonstrates that a convergence between PC and mobile gaming is virtually inevitable. The parallels between Android and SteamOS are many: both use OpenGL as the graphics API of choice, both are open platforms." Trine 2 running on Tegra K1 reveals a 720p game that targets 30fps, while running with the same quality settings as the PC and PS4 versions. That's not a mock-up shot by the way, but a screenshot of Nvidia's keynote, with the game running in real-time. However, all the signs point to Windows as nothing more than a bit player in the mobile market, automatically limiting the ability for Steam to expand beyond desktop and laptop PCs. Microsoft's efforts to break into the smartphone and tablet space have fallen well short, and it seems extremely unlikely that this scenario will change in the next few years. With Android so strongly established, the arguments for developers to shift from Windows/DirectX to Linux/Android and OpenGL look overwhelming in the longer term. But to be clear, we're talking about a process that is going to take years to evolve. Right now, the power of Tegra K1 is the exception, not the norm, and there remains the issue of the control interface not being up to scratch, with touchscreens not best suited to traditional PC games. Gabe Newell has already put some thought into this - he sees the touchscreen as a transitional interface for mobile devices, that it's a work-in-progress that will be replaced with a finer, more granular interface within the next decade. "When you start thinking about a platform, you have to address it. You have to address mobile. You have to look at what's going to happen post-tablet. If you look at the mouse and keyboard, it was stable for about 25 years. I think touch will be stable for about 10 years," he said. "I do think you'll have bands on your wrists, and you'll be doing stuff with your hands... your hands are incredibly expressive. If you look at somebody playing a guitar versus somebody playing a keyboard, there's a far greater amount of data that you can get through the information that people convey through their hands than we're currently using... Touch is... it's nice that it's mobile. It's lousy in terms of symbol rate." For the hardcore gaming purists who must use a joypad, doubtless there'll be new Nvidia Shield-like devices to fill the handheld void. Indeed, Nvidia has strongly hinted that K1 will be integrated into a Shield 2 device later this year. However, in the meantime, Valve's ambitions are rather more modest. There's another platform they're thinking about. And clearly, they're addressing it.