106 lines
4.2 KiB
TypeScript
106 lines
4.2 KiB
TypeScript
import { STRIDE, type Mesh } from "../engine/scene/Mesh"
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/** A procedural heightfield surrounding the room. It is the single source of
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* ground height: the outdoor mesh is built from it and the player stands on the
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* same `height` samples, so what you see and what you collide with agree. The
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* center (out to `inner`) is a flat clearing where the room sits; from there the
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* land rolls outward and ramps up into tall peaks at the far edge. Every field
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* is a live knob -- edit them in the level to reshape the world. */
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export type Terrain = {
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/** Half-extent of the flat central clearing (the room lives here); height 0. */
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inner: number
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/** World half-extent. Peaks ramp up toward this outer rim. */
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outer: number
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/** Ease-up distance just outside `inner`, so the clearing meets the hills with
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* a slope instead of a wall. */
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blend: number
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/** Rolling-hill height across the open ground. */
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amplitude: number
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/** Rolling-hill frequency (low = broad hills over the big world). */
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frequency: number
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/** Extra height of the mountains near the edge -- make this big for peaks. */
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peakHeight: number
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/** Mountain frequency (low = few, massive ridges). */
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peakFrequency: number
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/** Fraction of the way out (0..1) where the peaks begin rising. */
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peakStart: number
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}
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export namespace Terrain {
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/** Ground height at world (x, z). 0 inside the clearing, rolling hills beyond,
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* ramping into peaks toward the edge. Uses a square (Chebyshev) radius so the
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* clearing is a square that lines up with the square room. */
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export function height(t: Terrain, x: number, z: number): number {
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const r = Math.max(Math.abs(x), Math.abs(z))
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if (r <= t.inner) {
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return 0
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}
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const rise = smoothstep(t.inner, t.inner + t.blend, r)
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const hills = t.amplitude * bumps(x, z, t.frequency)
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const k = Math.min(1, (r - t.inner) / (t.outer - t.inner))
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const peaks = t.peakHeight * ridges(x, z, t.peakFrequency) * smoothstep(t.peakStart, 1, k)
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return rise * (hills + peaks)
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}
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/** Append one ground patch: a `cols`x`rows` heightfield grid over the rectangle
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* [x0,x1] x [z0,z1], each vertex lifted onto the heightfield. Quads whose
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* center is inside the clearing are skipped (the room floor's hole). UVs use
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* world position * `uvScale`, so neighboring patches tile seamlessly. Callers
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* keep the spacing uniform and cell edges aligned, so shared edges weld with
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* no cracks. Used to build the terrain per spatial chunk. */
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export function patch(
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t: Terrain,
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mesh: Mesh,
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x0: number,
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z0: number,
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x1: number,
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z1: number,
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cols: number,
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rows: number,
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uvScale: number,
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): void {
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const base = mesh.verts.length / STRIDE
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const dx = (x1 - x0) / cols
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const dz = (z1 - z0) / rows
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const rowLen = cols + 1
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for (let i = 0; i <= rows; i++) {
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const z = z0 + i * dz
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for (let j = 0; j <= cols; j++) {
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const x = x0 + j * dx
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mesh.verts.push(x, height(t, x, z), z, x * uvScale, z * uvScale)
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}
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}
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for (let i = 0; i < rows; i++) {
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for (let j = 0; j < cols; j++) {
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const cx = x0 + (j + 0.5) * dx
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const cz = z0 + (i + 0.5) * dz
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if (Math.max(Math.abs(cx), Math.abs(cz)) < t.inner) {
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continue
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}
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const p = base + i * rowLen + j
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// Wound so the surface faces up/out, matching the backface-cull sign.
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mesh.indices.push(p, p + rowLen + 1, p + 1, p, p + rowLen, p + rowLen + 1)
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}
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}
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}
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/** Rolling hills in 0..1, always non-negative so the ground never dips below
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* the clearing. */
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function bumps(x: number, z: number, f: number): number {
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const a = Math.sin(x * f) * Math.cos(z * f)
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const b = Math.sin((x + z) * f * 0.5 + 1.7) * 0.5
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return (a + b + 1.5) / 3
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}
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/** Ridged noise in 0..1: crests where the field crosses zero give sharp
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* mountain ridgelines rather than round blobs. */
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function ridges(x: number, z: number, f: number): number {
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const n = Math.sin(x * f + 1.3) * Math.cos(z * f - 0.7) * 0.7 + Math.sin((x + z) * f * 0.6 + 2.5) * 0.3
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return 1 - Math.abs(n)
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}
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function smoothstep(a: number, b: number, x: number): number {
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const t = Math.max(0, Math.min(1, (x - a) / (b - a || 1e-4)))
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return t * t * (3 - 2 * t)
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}
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}
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