terrain_fbm

Domain-warped fractal noise written into one scalar channel of one tile.

Gradient noise with quintic interpolation. Sample positions come from the field-wide cell index, the field's minimum corner, and the seed, so a tile evaluated on its own is identical to the same tile evaluated as part of the whole field — and a cell reached as one tile's apron lands on exactly the world position it has as its neighbour's interior.

featureSize is the world size in metres of the largest noise feature. Halving resolution therefore refines the same landscape instead of producing a different one.

warp is a world distance: how far the domain is displaced by two lower-octave fields before the main fractal is sampled. Non-zero warp is what turns isotropic lumps into ridgelines and basins.

ridge folds the fractal about zero and squares it, giving sharp crests and rounded valleys.

blend decides how the contribution meets what the channel already holds: replace, add, max, or min.

Every op carries a mask. The op's weight at a cell is scaled by what the mask reads there — multiplied in, or subtracted out — so the op applies only where the mask lets it and a cell the mask holds out keeps exactly what it already held, at every blend mode. An op that names no mask writes at full strength everywhere.