Fields and layers

One kind of data flows along every connection in Ymir: a field. A field is a grid of values covering the world, and every node takes fields in and hands fields out. Because the type is always the same, a node drops in anywhere a field is available, and you are never forced into a fixed build order.

A field carries named layers. The height layer is the terrain itself, and it is the one almost every node reads and writes. Other layers ride alongside it: a mask that scopes where an effect applies, or the flow, wear, and deposition that erosion produces as it runs. A node that changes the height passes every other layer through untouched, so inserting it never loses the work upstream of it.

The height convention

Height is a plain number in the working range [0, 1]: 0 is the lowest ground, 1 the highest. This is a convention, not a wall. A node is free to push values above 1 or below 0, and the range is only resolved to real elevation at the end, by World height on export and by the display when you look at the terrain.

Two habits follow from this. Judge a terrain by its shape and its relative heights, not by an absolute number, because the mapping to metres happens later. And when a value leaves the range, do not reach for a clamp out of reflex: the range is meant to be exceeded in passing, and clamping throws away detail an export or a later node could have used.