This summer Microsoft gave further details on its next graphics API: DirectX 11 or should we say Direct3D 11. As you’ll remember, the main innovations with this API are the hardware-based tessellation, new shader technology, the Compute Shader, and a recasting of the API for better multi-threading rendering.
The tessellation unit allows a refinement of geometry to avoid the angular shape of objects and landscapes by subdividing the geometry. This more complex meshing can also be used to add details via Displacement Mapping. The Xbox 360 GPU as well as all the Radeon HDs have a dedicated tessellation unit. This won’t however be compatible with DirectX 11, which needs more programmability.
The programmer doesn’t control how the tessellation unit itself calculates but works with 2 new types of shaders, the Hull Shader and the Domain Shader, which come before and after the tessellation unit in the pipeline. This makes DirectX 11 a tessellation superset of the Radeon HDs. Another way of putting it is to say that using it today alongside the Radeon HDs will allow developers to reuse and extend their work with DirectX 11, which means they might finally get interested.
The Compute Shader is a type of shader given over to more or less general calculation. It can work outside the graphics pipeline but can also interface easily with it. Its structure is very close to CUDA, which Microsoft probably modelled them on. It should facilitate physx support for GPUs as well as image processing because of the use of a standardised language open to all.
On the subject of the new features of DirectX 11, critics will note that it uses 3 new types of specific shaders as well as one new dedicated unit, which does somewhat go against current 3D rendering thinking…
Using the API to better exploit multicore CPUs is probably the most promising aspect of the DirectX 11. One linked point that has gone almost unnoticed is that DirectX 11 will reintroduce DirectX 9 support.
Microsoft wiped the slate clean with DirectX 10, the DirectX 10 not giving anything except DirectX 10 graphics card support. With DirectX 11, the DX10.1, DX10 and DX9 can all be used, limited of course in the features they support and via a new driver.
DirectX 9 being very different from DirectX 10 in terms of the API, it remains to be seen how well it will perform. The DX9 will probably have limited functionality, Shader 3.0 (without any options) and altogether with a lower performance than going through the native DX9 API. The work of developers will however be much simplified and it is possible that an improved use of multicore CPUs will be ample compensation for reduced effectiveness. Obviously Nvidia, AMD and Intel will have to develop DirectX 11 pilots for their DirectX 9 cards for everything to fall into place.
