@thi.ng/shader-ast-stdlib/sdf/polygon.js

Function collection for modular GPGPU / shader programming with @thi.ng/shader-ast

import { F, V2 } from "@thi.ng/shader-ast/api/types";
import { assign } from "@thi.ng/shader-ast/ast/assign";
import { forLoop, ifThen } from "@thi.ng/shader-ast/ast/controlflow";
import { defn, ret } from "@thi.ng/shader-ast/ast/function";
import { index } from "@thi.ng/shader-ast/ast/indexed";
import { FLOAT1, INT0, bvec3, int } from "@thi.ng/shader-ast/ast/lit";
import {
  div,
  gt,
  gte,
  inc,
  lt,
  mul,
  neg,
  not,
  or,
  sub
} from "@thi.ng/shader-ast/ast/ops";
import { $x, $y } from "@thi.ng/shader-ast/ast/swizzle";
import { sym } from "@thi.ng/shader-ast/ast/sym";
import { _any, all } from "@thi.ng/shader-ast/builtin/bvec";
import { dot, minSelf, sqrt } from "@thi.ng/shader-ast/builtin/math";
import { clamp01 } from "../math/clamp.js";
const sdfPolygon2 = (N) => defn(
  F,
  `sdfPolygon2_${N}`,
  [V2, ["vec2[]", "pts", { num: N }]],
  (p, pts) => {
    let d, s;
    let b, e, w, t;
    let pi, pj;
    let c;
    let j;
    return [
      t = sym(sub(p, index(pts, 0))),
      d = sym(dot(t, t)),
      s = sym(FLOAT1),
      j = sym(int(N - 1)),
      forLoop(
        sym(INT0),
        (i) => lt(i, int(N)),
        inc,
        (i) => [
          pi = sym(index(pts, i)),
          pj = sym(index(pts, j)),
          e = sym(sub(pj, pi)),
          w = sym(sub(p, pi)),
          b = sym(
            sub(w, mul(e, clamp01(div(dot(w, e), dot(e, e)))))
          ),
          minSelf(d, dot(b, b)),
          c = sym(
            bvec3(
              gte($y(p), $y(pi)),
              lt($y(p), $y(pj)),
              gt(mul($x(e), $y(w)), mul($y(e), $x(w)))
            )
          ),
          ifThen(or(all(c), not(_any(c))), [assign(s, neg(s))]),
          assign(j, i)
        ]
      ),
      ret(mul(s, sqrt(d)))
    ];
  }
);
export {
  sdfPolygon2
};