Mobile gaming was long dominated by Nintendo with Sony coming in a distant second.  That was until Apple stormed onto the scene with its iPhone and stole the show.  Today the iPhone is arguably mobile gaming's most influential platform.

Microsoft hopes to steal Apple's thunder when it releases Windows Phone 7 Series phones later this year.  This week Microsoft shared some details about what gaming on the new operating system will look like.

Unlike the Zune and Courier prototype, which are both powered by NVIDIA's Tegra, most Windows Phone 7 Series phones will use a Qualcomm SnapDragon chipset that contains a GPU from NVIDIA-rival AMD.  The GPU, the AMD Z430, features a unified pixel & vertex shader pipeline (based on the Xbox 360 Xenos GPU).

Unfortunately, developers won't be able to use the GPU's shaders in 3D game titles at launch.  However, an update to Direct 3D Mobile will provide this functionality sometime late this year or early next year.  Describes Microsoft's Shawn Hargreaves in a blog, "

The phone supports full hardware accelerated 3D, but we are not exposing programmable shaders in this release. Charlie Kindel summed up the reason for that in a great article about focus and priorities:

“We will do a few things and do them very, very well; we are better off not having a capability than doing it poorly. There are always future versions.”

Instead of programmable shaders, we augmented the existing BasicEffect with four new configurable effects: SkinnedEffect, EnvironmentMapEffect, DualTextureEffect, and AlphaTestEffect. These are designed to run efficiently on the mobile GPU hardware, and I think do a good job of providing enough flexibility for developers to create awesome looking games, while also meeting our goals of being able to ship a robust and well tested product on schedule.

Microsoft is offering developers two screen resolutions -- a 480×800 (WVGA) display resolution and a 320×480 (HVGA).  The HVGA resolution will come post-launch as an update.  Developers can pick which resolution to run, and Microsoft is dictating that its handset partners use dedicated scaling hardware to prevent GPU resources from being gobbled up and to provide better quality scaling.  Touch input will automatically scale with whatever resolution you pick.  

For example, if a user with a WVGA phone fires up a HVGA iPhone port on a Windows Phone 7 Series phone with a high resolution screen, the hardware will seamlessly scale the game up.  This allows game developers flexibility and potentially better performance.  Describes Hargreaves, "480×800 is a lot of pixels! This is a great resolution for displaying text, browsing the web, etc, but it can be a challenge for intensive 3D games to render so much data at a good framerate. To boost performance, some games may prefer to render at a lower resolution, then scale up to fill the display."

According to a separate Joystiq interview with Xbox Live GM Ron Pessner and XNA Game Studio manager Michael Klucher, developers will have two options for writing games -- Silverlight (Microsoft's Flash competitor) or the XNA Game Studio and the XNA framework.  Developers can reuse assets, but they will have to port their efforts in Java or Flash to these new platforms.  Silverlight games will be fully able to access Microsoft's Xbox Live gaming service.

One final tidbit is that it sound like it will be ridiculously easy to use Microsoft XNA Game Studio to port Zune titles to Windows Phone 7 Series phones and vice versa.  States Microsoft, "Another big point is -- just like the portability piece we've shown here -- we've done some work internally and with some of the other Zune HD developers, and again, it's 90, 95 percent code reuse. Literally, in an hour or couple of hours, we're taking games that were written for Zune HD and putting them on the phone. We can do the same in reverse. Game Studio is a really powerful platform for portability between these different devices. We think there will be a series of developers that will want to target both platforms and Game Studio gives them a really great way of doing that."

While it may be a bit of work to port iPhone titles to Windows Phone 7 Series, it certainly seems like a tempting target, given its ability to exploit higher screen resolutions and likely larger amounts of texture memory.  This is good news for Windows Phone 7 Series, as a lot of the iPhone's popularity has been due to its gaming success.