ExtremeTech has just published a lengthy interview with two of the key players in Microsoft’s deployment of DirectX 10. They speak to Chris Donahue, Director in the Games for Windows Entertainment and Devices Division, and David Blythe, Software Architect in the Graphics Platforms Unit. The result is a fairly technical drill down into what DirectX 10 promises to bring to the end user.

More details after the jump.

Though the focus on DirectX 10 definitely has to be the improved graphics capabilities, there are some other changes, particularly the inclusion of the XInput API. XInput is the method by which Xbox controllers were handled, and apparently this will be the preferred method of interaction over the legacy DirectInput.

According to Blythe, there isn’t one particular “killer feature” driving DirectX 10, but the goal was to rework the API to eliminate inefficiencies while adding new features to support the next generation of graphics and physics processing. While resolving the “small batch problem” may not be as sexy as adding new rendering modes, this goes a long way in improving how games display.

Other new features include a new integer instruction set, which hasn’t been seen in other APIs to this point, and the addition of geometry shaders. The integer instruction set should be helpful in managing the shader paths. The new geometry shaders will further increase the flexibility of the rendering path; one example would be easier implementation of particle systems under the new API.

Blythe further talks about why DirectX had to be Windows Vista exclusive. This was certainly something that was considered in the development process, but the changes in DirectX really require a number of the changes that are happening to the driver model in Vista. If Microsoft implemented DirectX 10 on XP, gamers would probably “end up with something that, from an API point of view it might not be that different, but… you might not get nearly as dramatic an improvement…” At some point, Microsoft was going to have to re-architect DirectX to keep up with technology, and the Vista break point seemed to be an ideal time to do this.

According to Microsoft, the improvements one would see will include “…greater complexity and more detail in the game… Better foliage, better grass, more rocks, more trees.” Further, “being able to generate data inside the [graphics] processor and then be able to add specific shading parameters or… change the geometry on a per-instance basis… adds to the level of complexity…” Some of the improvements will mean that in addition to the previously mentioned instancing, and particle maps, shadow volumes and displacement maps will be easier to implement. Texture sizes increases will allow gamers to take advantage of the increased memory on graphics cards today.

The interview offers a ton of insight into the development process behind DirectX 10, and in the next few days, ExtremeTech will be talking to graphics card developers to see how the API translates into the hardware.