Half-Life 2 Performance Benchmark Preview

More on Mixed-Mode for NV3x

We briefly mentioned the Mixed Mode of operation for NV3x GPUs that Valve implemented in Half-Life 2, but there is much more to it than just a special NV3x code path. In fact, the mixed mode NV3x code path was really only intended for the GeForce FX 5900 Ultra (NV35). The mainstream FX chips (5200/5600) require a slightly different code path.

Here you can see the 40% performance boost NVIDIA gets from the special NV3x code path.

The GeForce FX 5600 (NV31) uses a code path that is internally referred to as dx82; this path is a combination of DX9 (pixel shader 2.0) and DX8.1 (pixel shader 1.4) code, and thus, doesn't look as good as what you'll see on the 5900 Ultra.

Although the 5900 Ultra performs reasonably well with the special NV3x mixed mode path, the 5600 and 5200 cards do not perform well at all. Valve's recommendation to owners of 5600/5200 cards is to run the DX8 (pixel shader 1.4) code path in order to receive playable performance under Half-Life 2. The performance improvement gained by dropping to the DX8 code path is seen most on the GeForce FX 5200; although, there is a slight improvement on the 5600 as you can see below:

The sacrifices that you encounter by running either the mixed mode path or the DX8 path are obviously visual. The 5900 Ultra, running in mixed mode, will exhibit some banding effects as a result of a loss in precision (FP16 vs. FP32), but still looks good - just not as good as the full DX9 code path. There is a noticeable difference between this mixed mode and the dx82 mode, as well as the straight DX8 path. For example, you'll notice that shader effects on the water aren't as impressive as they are in the native DX9 path.

Are the visual tradeoffs perceptive? Yes. The native DX9 path clearly looks better than anything else, especially the DX8.0/8.1 modes.