worldlisted

# The world Three coordinate spaces — **grid**, **world**, **screen** — and every operation here is only correct because it knows which one it is in. Game code never converts between them by hand; every conversion is a named function that takes an output parameter. Two facts that decide most of what follows: - **Tile lookup floors, never rounds.** Rounding snaps to the nearest lattice vertex and picks the wrong tile for three quarters of every diamond. - **Elevation lives on grid vertices, not tile centers.** Adjacent tiles therefore share their corner values exactly and cannot leave a seam — and once `z` exists the projection is no longer invertible, so picking has to be terrain-aware. That is the biggest trap in this skill and it has its own section. --- ## Ground, and height on it ```ts import { TileGrid, footprintBase, heightAt, slopeAt, tileSourceOf } from '@latticekit/iso'; import type { Footprint, HeightField } from '@latticekit/iso'; import { fbm2 } from '@latticekit/core'; const W = 96; const H = 96; // One value per grid VERTEX, so the grid is one wider than the tile map in each axis. const heights = new TileGrid(W + 1, H + 1); heights.fillFrom((gx, gy) => Math.max(0, fbm2(1234, gx * 0.04, gy * 0.04, 4) * 8)); /** `stepPx` is world pixels per height unit — the one conversion between the game's units * and the projection's. 8 means a ridge of 5 units stands 40 world pixels proud. */ const land: HeightField = { heights, stepPx: 8 }; /** The tallest