With DirectX 10, the chips of graphics cards (GPUs) started to be able to do other tasks than just displaying graphics. Their big amount of “cores” enabled GPUs to compute different kinds of tasks much faster than a CPU would be able to. Nvidia offered CUDA to do video-encoding, matrix-multiplication or Folding@Home. ATI offered basically the same calling it Stream.
Now more and more developers are using these possibilities to enhance the visual quality of games, e.g. for physics calculation with Nvidia’s PhysX framework or possibly in the future with the open-source alternative OpenPhysics. But GPU acceleration can also greatly enhance the quality of water in games. The game Just Cause 2 offers support for GPU Water Simulation and shows quite impressively the differences between “normal” and “GPU” water.
Video Comparison:
Screenshot Comparison:
Let’s start with some screenshots for comparison (click on the image for full resolution):
As you can see, the visual quality improves quite a lot. But how does this GPU acceleration affect the performance?
Benchmarking System:
- Processor: AMD Phenom II X4 955 (3.2GHz)
- Mainboard: Gigabyte GA-MA790XT-UD4P
- Memory: 2×2GB A-Data DDR3-1333 (CL 7-7-7-24 2T)
- Graphics: Gainward Nvidia GTX 260 (680/1400/1150MHz)
- Hard Disk: Samsung Spinpoint F3 1000GB (7200RPM, 32MB cache)
- Operating System: Windows 7 Ultimate 64-bit
- Ingame Settings: 1920×1080, advanced settings as follows:
Performance Assessment
In order to measure the performance loss for enabling GPU Water Simulation in Just Cause 2, I took three common situations and measured the framerates for an interval of time:
Falling: Airlift to Bandar Arang Batu Besar (24676/27047), straight fall into death
Flying: Flight from Kem Udara Wau Pantas (22217/23304) to Pelantar Gas Panau Seladan (29886/24713) for 30 seconds, high above the water
Base Jump: Jump from highest skyscraper in Panau City – Docks District (1116/13726) in northern direction until death
The following diagram shows the actual testing results:
The framerates dropped quite significantly on my system (details above), on average the GPU Water Simulation lowered the FPS by 40%. When flying high above the water the game was still running fast enough, but especially in the city with an average of 19 FPS and a minimum FPS of 16, the game became unplayable.
Conclusion
GPU Water Simulation really improves the visual quality of games, but also needs a lot of computing power and thus lowers the performance significantly. On my system the game Just Cause 2 was not playable with GPU Water Simulation enabled in scenes with much action or geometry. Thus it takes a really powerful computer in order to be able to enjoy the great quality of GPU-accelerated water.
Source files of benchmarks: JustCause2_GPU_Water.rar