I'm researching the theory behind the NVIDIA SDK sample "FFT Ocean" which is based on this paper:
It gives an explicit formula for evaluating the surface heights at a given time t. As the NVIDIA demo shows, you can do FFT in real-time and animate the ocean, and the performance is pretty good. However, I am wondering if it still takes too much GPU resources, as ocean is only part of a 3d game scene like a crysis level. So in practice, do people just use the FFT method to build several heightmaps, and then scroll the heightmaps at different speeds to animate the waves? The NVIDIA SDK also has an "Island" demo, and I looked at the water shader, and it appears they are just scrolling heightmaps and not doing the FFT ocean in real-time.