meat/app/level.ts

import { Color } from "../engine/render/Color"
import type { CloudLayer, SkyConfig } from "../engine/render/Sky"
import type { Mesh } from "../engine/scene/Mesh"

type Corner = [number, number, number]

/** Axis-aligned solid. Blocks the player horizontally while their feet are
 *  below `top`; if `standable`, its `top` also counts as ground to land on. */
export type Aabb = {
  minX: number
  maxX: number
  minZ: number
  maxZ: number
  top: number
  standable: boolean
}

/** The playground: geometry split by texture, its collision solids, where the
 *  NPC stands, and the sky to draw behind it. */
export type Level = {
  floor: Mesh
  walls: Mesh
  crate: Mesh
  colliders: Aabb[]
  npcPosition: { x: number; y: number; z: number }
  sky: SkyConfig
}

const ARENA = 12
const WALL_HEIGHT = 4
const CRATE = { x: -2, z: -2, half: 1, top: 1 }

/** Triangle density: grid divisions per world unit, applied to every textured
 *  surface (floor, walls, crate). Higher = smaller triangles = each spans less
 *  depth = less affine texture swim, at the cost of more geometry; lower =
 *  chunkier, wilder PS1 warp (below ~0.5 the floor tips into the black-wedge
 *  degeneration). Because it scales with surface size, one value keeps the big
 *  floor and the little crate equally warp-free. Edit and Vite reloads. Pairs
 *  with the `ps1` preset's `perspectiveCorrect`, which fights the same error
 *  from the render side. */
const DIVISIONS_PER_UNIT = 1.3

/** The two cloud styles; swap which one the sky uses in `buildLevel`.
 *  `basicCumulus` is cheap flat puffs; `fancyCumulus` is the pricier
 *  heightfield-shaded, domain-warped version with faked volume. */
export const basicCumulus: CloudLayer = {
  kind: "basic",
  color: Color.rgb(248, 250, 255),
  coverage: 0.5,
  scale: 0.9,
  speed: 0.5,
  edge: 0.02,
}

export const fancyCumulus: CloudLayer = {
  kind: "fancy",
  color: Color.rgb(250, 251, 255),
  coverage: 0.5,
  scale: 0.6,
  speed: 0.5,
  edge: 0.02,
  warp: 0.4,
  relief: 7,
}

export function buildLevel(): Level {
  const floor = mesh()
  quadGrid(floor, [-ARENA, 0, -ARENA], [ARENA, 0, -ARENA], [ARENA, 0, ARENA], [-ARENA, 0, ARENA], 12, 12)

  const walls = mesh()
  const h = WALL_HEIGHT
  // Inward-facing perimeter, no ceiling so the sky shows above.
  quadGrid(walls, [-ARENA, 0, -ARENA], [ARENA, 0, -ARENA], [ARENA, h, -ARENA], [-ARENA, h, -ARENA], 12, 2.5)
  quadGrid(walls, [ARENA, 0, ARENA], [-ARENA, 0, ARENA], [-ARENA, h, ARENA], [ARENA, h, ARENA], 12, 2.5)
  quadGrid(walls, [ARENA, 0, -ARENA], [ARENA, 0, ARENA], [ARENA, h, ARENA], [ARENA, h, -ARENA], 12, 2.5)
  quadGrid(walls, [-ARENA, 0, ARENA], [-ARENA, 0, -ARENA], [-ARENA, h, -ARENA], [-ARENA, h, ARENA], 12, 2.5)

  const crate = mesh()
  box(crate, CRATE.x, CRATE.z, CRATE.half, CRATE.top)

  const colliders: Aabb[] = [
    wall(-ARENA, ARENA, -ARENA, -ARENA + 1),
    wall(-ARENA, ARENA, ARENA - 1, ARENA),
    wall(ARENA - 1, ARENA, -ARENA, ARENA),
    wall(-ARENA, -ARENA + 1, -ARENA, ARENA),
    {
      minX: CRATE.x - CRATE.half,
      maxX: CRATE.x + CRATE.half,
      minZ: CRATE.z - CRATE.half,
      maxZ: CRATE.z + CRATE.half,
      top: CRATE.top,
      standable: true,
    },
  ]

  const sky: SkyConfig = {
    zenith: Color.rgb(58, 108, 196),
    horizon: Color.rgb(178, 198, 226),
    sun: Color.rgb(255, 246, 214),
    sunDir: { x: 0.3, y: 0.5, z: -0.8 },
    sunSize: 0.04,
    clouds: basicCumulus,
  }

  return { floor, walls, crate, colliders, npcPosition: { x: 2, y: 0, z: -1 }, sky }
}

function mesh(): Mesh {
  return { vertices: [], indices: [] }
}

function wall(minX: number, maxX: number, minZ: number, maxZ: number): Aabb {
  return { minX, maxX, minZ, maxZ, top: WALL_HEIGHT, standable: false }
}

/** Tessellate a quad into a grid sized by DIVISIONS_PER_UNIT, so triangle size
 *  (and thus affine warp) is consistent whatever the surface's scale. Corners
 *  run a (uv 0,0) -> b (us,0) -> c (us,vs) -> d (0,vs). */
function quadGrid(m: Mesh, a: Corner, b: Corner, c: Corner, d: Corner, us: number, vs: number): void {
  const nu = divisions(a, b)
  const nv = divisions(a, d)
  const base = m.vertices.length
  const row = nu + 1
  for (let i = 0; i <= nv; i++) {
    const t = i / nv
    for (let j = 0; j <= nu; j++) {
      const s = j / nu
      const wa = (1 - s) * (1 - t)
      const wb = s * (1 - t)
      const wc = s * t
      const wd = (1 - s) * t
      m.vertices.push({
        pos: {
          x: a[0] * wa + b[0] * wb + c[0] * wc + d[0] * wd,
          y: a[1] * wa + b[1] * wb + c[1] * wc + d[1] * wd,
          z: a[2] * wa + b[2] * wb + c[2] * wc + d[2] * wd,
        },
        uv: { x: us * s, y: vs * t },
      })
    }
  }
  for (let i = 0; i < nv; i++) {
    for (let j = 0; j < nu; j++) {
      const p = base + i * row + j
      m.indices.push(p, p + 1, p + row + 1, p, p + row + 1, p + row)
    }
  }
}

/** Grid divisions along edge a->b, from its world length and the density. */
function divisions(a: Corner, b: Corner): number {
  const length = Math.hypot(b[0] - a[0], b[1] - a[1], b[2] - a[2])
  return Math.max(1, Math.round(length * DIVISIONS_PER_UNIT))
}

/** A box centered at (cx, cz) on the floor: top face plus four sides, one uv
 *  tile per face. No bottom (never seen). Tessellated like every other surface,
 *  so it no longer warps up close. */
function box(m: Mesh, cx: number, cz: number, half: number, top: number): void {
  const x0 = cx - half
  const x1 = cx + half
  const z0 = cz - half
  const z1 = cz + half
  quadGrid(m, [x0, top, z0], [x1, top, z0], [x1, top, z1], [x0, top, z1], 1, 1)
  quadGrid(m, [x0, 0, z0], [x1, 0, z0], [x1, top, z0], [x0, top, z0], 1, 1)
  quadGrid(m, [x1, 0, z1], [x0, 0, z1], [x0, top, z1], [x1, top, z1], 1, 1)
  quadGrid(m, [x1, 0, z0], [x1, 0, z1], [x1, top, z1], [x1, top, z0], 1, 1)
  quadGrid(m, [x0, 0, z1], [x0, 0, z0], [x0, top, z0], [x0, top, z1], 1, 1)
}