import PatternsDemo from './components/PatternsDemo.astro'

# Patterns

<PatternsDemo />

## Generator functions

A generator is just a function that returns a Mesh:

```ts
function tree(options?: { height?: number; seed?: number }): Mesh {
  const rand = createRng(options?.seed ?? 1)
  const trunk = cylinder({ radius: 0.05, height: height * 0.4 })
    .translate(0, height * 0.2, 0)
    .vertexColor([0.35, 0.22, 0.1])
  const canopy = icosphere({ radius: 0.5 })
    .translate(0, height * 0.6, 0)
    .faceColor(...)
  return merge(trunk, canopy)
}
```

## Seeded randomness

Use `createRng` (wraps alea PRNG) for deterministic generation:

```ts
import { createRng } from 'shapecraft'

const rand = createRng(42)       // seed → deterministic sequence
rand()                           // 0-1
rand()                           // next value

// Derive sub-seeds for noise, jitter, etc.
function subSeed() { return Math.floor(rand() * 2147483647) }
const noise = new UberNoise({ seed: subSeed() })
mesh.jitter(0.05, { seed: subSeed() })
```

**Important:** always consume `rand()` / `subSeed()` calls in the same order regardless of options, so changing one parameter doesn't shift the entire random sequence.

## Option schemas & presets

Define configurable generators with typed schemas:

```ts
import { resolveOptions, type OptionSchema } from 'shapecraft'

const treeSchema = {
  height:     { type: 'range',   default: 2.5, min: 0.5, max: 6, step: 0.1 },
  seed:       { type: 'integer', default: 1,   min: 1,   max: 100 },
  lean:       { type: 'range',   default: [0.1, 0.4], min: 0, max: 1 },  // randomized range
  showCanopy: { type: 'boolean', default: true },
  colors:     { type: 'color-array', default: ['#1a5a10', '#2a7518'] },
} satisfies OptionSchema

const presets = {
  default: {},
  autumn: { colors: ['#c44422', '#d48825'] },
  winter: { colors: ['#4a4a4a'], snowColors: ['#e8e8f0'] },
}

function tree(options = {}) {
  const rand = createRng(options.seed ?? 1)
  const o = resolveOptions(treeSchema, options, presets, rand)
  // o.height is a number, o.lean is resolved from [min,max] via rand
}
```

Numeric defaults can be `[min, max]` — resolved deterministically from the seed. The editor shows the midpoint.

## Scatter points

```ts
import { scatterOnSphere } from 'shapecraft'

// N random points on a sphere surface
const points = scatterOnSphere(5, seed, {
  radius: 1,
  polarMin: Math.PI * 0.3,  // avoid top
  polarMax: Math.PI * 0.7,  // avoid bottom
})
// → [[x,y,z], [x,y,z], ...]
```

## Terrain workflow

```ts
const terrain = plane({ size: 20, segments: 100 })
  .displaceNoise(fbm({ seed: 42, scale: 0.2, octaves: 5 }), 3)
  .vertexColor(heightGradient([
    [0, [0.2, 0.5, 0.1]],
    [1.5, [0.5, 0.35, 0.2]],
    [3, [1, 1, 1]],
  ]))
```

## Organic shapes with icosphere

```ts
// Subdivide → spherize → displace radially (no gaps)
icosphere({ radius: r, subdivisions: 0 })
  .subdivideAdaptive(edgeLen)
  .spherize(r)
  .displaceNoise(noise, r * 0.5, { direction: 'radial' })
  .jitter(r * 0.04, { seed })
```

Use `direction: 'radial'` instead of `'normal'` on non-indexed geometry to avoid gaps between faces.

## Branches & tubes

```ts
import { tube } from 'shapecraft'

// Tapered branch along a curved path
const path = [[0,0,0], [0.1,0.5,0], [0.3,1,0.1], [0.2,1.5,0]]
const branch = tube(path, (t) => 0.05 * (1 - t * 0.8), 5)
```

## Leaves with loft + thicken

```ts
import { loft, thicken } from 'shapecraft'

const leaf = loft({
  path: leafPath,
  shape: (t) => {
    const w = 0.2 * Math.sin(t * Math.PI)  // wide in middle
    return [[-w, 0], [0, w*0.2], [w, 0]]
  },
  closedShape: false,
  up: [0, 1, 0],
})
const solidLeaf = thicken(leaf, 0.01)
```