Creating biome areas

A biome area is an object that is not related to soils. Soils define densities, so this is the amount of vegetals of a given type that are going to be scattered by the system. However, among a given category of vegetals, there's no more detail on where these vegetals should appear or not.

A biome area is then another way to refine that initial density information, allowing to tell where a specific plant needs to appear. For instance, this can be used to create fields as illustrated below.

Biome areas are created using Decals. Polygonal decals can be created everywhere in the scene to define biome areas. So for instance, we can create a decal area called "wheat" or "sunflower" and also setup the wheat plant model of our biome to only appear in the "wheat" biome area.

So:

And in close-up, we can see the area definition job done by our areas:

Several remarks on this mechanism: by no way this modifies the density of plants displayed. It just acts as a filter on the candidate plants that can appear at a given place. To find out the vegetation coverage at a given location, the system will look for all candidate plants that can appear at that location. Then, it'll pickup one of them, among the available candidates. So we can see that this is a candidate selection filter, and not something else meant to change the density of the plants at the specified location.