The State of DirectX 11 - Image Quality & Performance

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Dirt 2: Image Quality



One of first DirectX 11 games to be released in North America, Dirt 2 also boasts one of the largest compliments of DirectX 11 features. The sequel to the original Dirt, Dirt 2 has already won high critical acclaim for its solid gameplay and excellent graphics. While some have commented that the game is less simulator and more arcade than its predecessor, most agree that the gameplay is fun and captures the enjoyment of rally racing well.

Dirt 2 is built on Codemaster's Ego Game Technology Engine, a modified version of the Neon game engine which powered the original Dirt. Unlike many of the other games featured in this article, Dirt 2's anti-aliasing is implemented in a way which allows AA in all DirectX levels. The game makes use of a large number of DirectX 11 features, as the following video illustrates.



Dirt 2 makes extensive use of tessellation, most notably in the cloth objects, like flags and banners, and in the spectator crowds. Unfortunately, both of these items play very small rolls in the game and the player is often only treated to brief glances of flags and crowd in their struggle for rally domination. We found that during normal gameplay, cloth objects like flags and banners, as well as the spectator crowd, were too far away from the camera for the benefits of tessellation to be noticeable. We actually had a hard time capturing a image quality difference in screenshots through normal gameplay, so it is not represented below in the comparison images.

   

Besides tessellation, Dirt 2 also implements a few other DirectX 11 goodies. Two other notable DirectX 11 features implemented by Dirt 2 are screen-space ambient occlusion (SSAO) and some post-processing filters. Dirt 2 uses high definition ambient occlusion (HDAO) which is AMD's implementation of SSAO. These effects can be observed on all manner of objects. They add extra depth to flat surfaces and their effects can be observed on the car bodies. In the first comparison image (above, left), the headlights of the car in DirectX 9 are relatively bright, despite being recessed in the body of the car. In DirectX 11, the HDAO algorithm correctly depicts the headlights as being in shadow, due to being blocked by the hood of the car.

These effects can also be observed in the second comparison image (above, right), where the body of the car reflects differently in DirectX 9 compared to 11. Note how the bottom of the "wing" on the rear of the car correctly reflects the ambient light reflecting from the top of the trunk in DirectX 11. Also note the lack of reflections on the car's rear window in DirectX 9. Finally, Dirt 2 performs some post-processing, and this can be observed in the shadow transitions, which are smooth in DirectX 11 but appear to be composed of discrete overlapping layers in DirectX 9.

   

While the implemented crowd and cloth tessellation was barely worth noting, we definitely did notice the tessellated water effects. The tracks were frequently covered by small pools of water which the cars were more than happy to splash through. The result is a tessellated wave which actually rose up and rippled. In contrast, in DirectX 9, the water remained relatively flat due to the lower level of geometry detail without tessellation. While this effect is best viewed in motion, like in the video, it can be observed in our last comparison image (above, right).

Overall, Dirt 2 is a very visually impressive game. The near photo-realistic graphics really lent a strong atmosphere to the game which helped to impart a real sense of "being there" to the player. While many of the tessellation effects won't be missed by DirectX 9 users, the lack of screen-space ambient occlusion and post processing will bring the image quality down a notch.

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