The solution was to show more detail in the rats closest to the player, and slowly fading them into the shadows as distance grows. The result was four levels of detail.In the fourth layer farthest back, the rats serve as a background non-animated mesh, but as they get closer, they start to share the same animation loop (third layer). In the second layer, one hundred rats are slightly less detailed than those in the first layer, closest to the players, where the rats are fully animated and detailed.
By merging calculations of the rats’ movement and reactions, the team was able to display more than 5,000 rats at once, and simulate an additional 5,000 behind the player. This was made possible by using multi-threading, with several processor cores working simultaneously.