This produces the natural, noised movement you see when the wind is not very strong. The simulation itself is the sum of a number of Perlin noise functions for the regular wind, and a very high-frequency "dephasing" function that makes the blades out of phase from their near neighbours. Once a group of squares has been generated in this way, we simulate them and upload them for drawing. This gives us a way to maintain artistic freedom, while avoiding unnecessary grass simulation and rendering.
The actual number of blades rendered in each square is dependent upon an artist-designed mask, and the distance from the camera.
This means that the number of blades rendered is effectively a density function. The world is divided into small square patches, each of which is rendered using data generated from a template patch, a square area filled with evenly-distributed grass blades. We didn’t want to simulate every blade of grass in the game world - that would be a bad idea. The limiting factor when it comes to creating realistic grass is the number of grass blades. Water surface simulation is a well-established algorithm, but you can always make it more interactive by adding CPU power to it, and that’s exactly what we had to spare. However, we started to think about how we could make the water more interactive so that it didn’t look out of place in the fields of swaying, interactive grass. Originally, we were planning to have minimal interaction with the water since it didn’t play an important part in battles - it was just there to make the landscape complete. This was the kind of simulation we could run on the CPU, and by either reducing the range or lowering the sim quality, we could make it scalable too.Īnother idea we had was to improve the water. If we could have grass that swayed realistically in a simulated wind system, and that interacted with dynamic objects in the game like the armed units and chariots, then we would have a significant increase in visual quality. We had a few brainstorming sessions with Intel, and one subject that kept coming up was the grass. Their plan fit well with ours, as our work to make 4K our rendering standard had pretty much saturated the GPU, and, since we had a few inherently single-threaded algorithms running on the CPU side, we had some idle cores to utilize. Intel was interested to see how we could use CPU capacity to push the realism of the environments, while at the same time ensuring that the game was equally playable on a wide range of systems.
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