Image Quality: DirectX 11 Enhancements
Hardware Tesselation: Water, Crowd, and Cloth
In layman's terms, hardware tessellation creates extra detail on simple 3D geometry where none would otherwise exist. Without devoting pages to theory, the best way to describe the effect is with pictures, each worth at least a thousand words:
DiRT 2 will apply hardware tessellation not only to the flags in the game, but also to the crowd and pools of water through which the cars drive.
Note how the water geometry is flat in DirectX 9 mode, while DirectX 11 allows for waves to be created out of tessellated geometry.
As for the crowd, the effect is subtle. Look at the character on the right side of the screen and note the hard edges of the geometry in DirectX 9 compared to the soft edges in DirectX 11. Also pay attention to the detail in the hands and fingers.
While hardware tessellation can be used for dramatic effects, it is extremely hard to notice in DiRT 2 because none of these elements are prominent while racing. For example, you never stop the car during a race to scrutinize a flag, the crowd, or the water as you drive through it. These subtle details speed by so quickly that they are almost impossible to spot while actually playing.
DirectCompute 11 Accelerated HD Ambient Occlusion
Ambient occlusion (AO) is a feature used to increase the realism of a game's lighting model. AO algorithms simulate the phenomenon where light has a hard time illuminating cracks and crowded spaces. A picture is also the best way to explain it:
While this enhances the lighting model very well, once again we have a feature that is difficult to spot in-game when everything is going by the camera quickly.
Full-Screen Resolution Post Processing
In DirectX 9 mode, some of DiRT 2's post-processing filters are run at one-quarter resolution to maintain high performance. However, in DirectX 11 mode, this post-processing is done at full resolution. The resulting quality increase is difficult to notice during daylight races, but is easy to notice in the night shots where a Gaussian glow filter is applied to lights.
Full Floating Point High Dynamic Range Lighting
Difficult to display in an image, DirectX 11 allows for a full floating point R16G16B16A16 texture when calculating high dynamic range lighting as opposed to the R8G8B8A8 fixed-point format used in DirectX 9 mode. This results in a theoretical bump in overall rendering quality, although the effect is so subtle that, again, it is difficult to demonstrate.