What Does DirectCompute Really Mean For Gamers?

What We Tested: Other Apps And Test Config

DiRT 3

DiRT 3 employs DirectCompute for its high-definition ambient occlusion (HDAO) effect. Unfortunately, there is no equivalent effect in the game based on pixel shading, so we can’t compare the two directly. However, the game offers three AO options. The first of these, “Low,” does offer occlusion rendered under cars via pixel shading. For the purposes of DirectCompute, this is effectively an “off” setting. The “High” setting employs HDAO at half-resolution, as discussed earlier. “Ultra” runs HDAO at full resolution. All other graphics options were set to either Low or, when possible, Off.

Metro 2033

The advanced depth of field (DOF) effect in Metro 2033 needs three rendering passes. Two of these employ pixel shading, while the third uses DirectCompute. The original clear image is combined with a blurred image to create a much more realistic, cinematic appearance that can add more of a 3D feel to games without a lot of the 3D cost and (sometimes literal) headache. The DoF feature is enabled/disabled via a checkbox in the game's benchmarking tool.

Civilization 5

Civilization 5 uses DirectX 11 and DirectCompute to leverage a variable bit rate texture codec algorithm. The algorithm is so efficient that 2 GB of leader textures compress down to less than 150 MB of disk storage.

“Textures on disk are stored in a Discrete Cosine Transfer-like format,” explains AMD’s Neal Robison. “In a nutshell, this means that texture data is stored in frequency space as it allows optimal compression, similar to the JPEG format. A shader is used to rapidly decompress this data in real-time and recompress it on-the-fly into a DCT texture format, which the GPU directly supports. This allows significant reductions in the texture storage requirements. More importantly, it allows significantly faster loading of high-quality and high-resolution textures into video memory compared to what a pure CPU implementation could provide. This is why the superb-looking leader scenes appear almost instantly in the game, regardless of how many civilizations are present.”

Civ5 contains an integrated benchmarking module designed to test this DirectCompute-based compression/decompression performance. You can find the tool’s usage detailed in the Civilization 5 benchmark modes.doc file within the Civilization 5 folder. By modifying a custom shortcut to the program, we used the following parameters: DX11_executable_filename –LeaderBenchmark –duration 90 –norendering. This loaded the benchmarking tool, ran it for 90 seconds, and did not allow for graphical output via compute. So, while the test is running, you can hear it, but the screen remains blank. To add DirectCompute and visual output back in, eliminate the –norendering parameter from the shortcut.

We kept our desktop test unchanged from the prior APU article, save for an update to the Asus Crosshair V Formula’s BIOS.