/** Floats per vertex in `Mesh.verts`: position x, y, z then texture u, v. */
export const STRIDE = 5

/**
 * Indexed triangle mesh, stored flat for speed. `verts` is a packed run of
 * `STRIDE` floats per vertex (x, y, z, u, v) instead of an array of nested
 * `{pos, uv}` objects, so the transform loop reads contiguous numbers with no
 * pointer chasing or per-vertex allocation. `indices` holds three vertex indices
 * per triangle (an index `i` addresses `verts[i * STRIDE ..]`); sharing vertices
 * keeps seams welded and shrinks the data. uv is in tile units, not 0..1, so
 * values >1 repeat the texture (see Texture.sample). Build with `Mesh.push`.
 */
export type Mesh = { verts: number[]; indices: number[] }

export namespace Mesh {
  export function create(): Mesh {
    return { verts: [], indices: [] }
  }

  /** Append a vertex, returning its index (for wiring up `indices`). */
  export function push(mesh: Mesh, x: number, y: number, z: number, u: number, v: number): number {
    const index = mesh.verts.length / STRIDE
    mesh.verts.push(x, y, z, u, v)
    return index
  }
}