run method

@override Vector4? run(Float32List v, ShaderBindings b, FragmentContext c)

Returns linear RGBA for attachment zero. Null discards the fragment.

Implementation

@override
Vector4? run(Float32List v, ShaderBindings b, FragmentContext c) {
  final bloom = b.textures['bloom_texture'];
  if (bloom == null) return Vector4(0.0, 0.0, 0.0, 1.0);
  final params = b.vec4('LensFlareInfo', 'params', Vector4.zero());
  final more = b.vec4('LensFlareInfo', 'more', Vector4.zero());

  // `Fringed`: the glow at (u, w), its channels taken [spread] apart.
  Vector3 fringed(double u, double w, double ax, double ay, double spread) =>
      Vector3(
        bloom.sample(u + ax * spread, w + ay * spread).x,
        bloom.sample(u, w).y,
        bloom.sample(u - ax * spread, w - ay * spread).z,
      );

  final glow = bloom.sample(v[0], v[1]);
  final flippedU = 1.0 - v[0];
  final flippedW = 1.0 - v[1];
  final towardU = (0.5 - flippedU) * params.z;
  final towardW = (0.5 - flippedW) * params.z;
  final reach = math.sqrt(towardU * towardU + towardW * towardW);
  final alongU = reach > 1e-6 ? towardU / reach : 0.0;
  final alongW = reach > 1e-6 ? towardW / reach : 0.0;
  final spread = more.x;

  final flare = Vector3.zero();
  final ghosts = (params.y + 0.5).floor();
  for (var i = 0; i < 8; i++) {
    if (i >= ghosts) break;
    final u = flippedU + towardU * i;
    final w = flippedW + towardW * i;
    flare.add(fringed(u, w, alongU, alongW, spread) * _falloff(u, w, 10.0));
  }

  final aspect = math.max(more.z, 1e-4);
  final haloU = flippedU + alongU / aspect * params.w;
  final haloW = flippedW + alongW * params.w;
  flare.add(
    fringed(haloU, haloW, alongU, alongW, spread) *
        (_falloff(haloU, haloW, 5.0) * more.y),
  );

  final intensity = params.x;
  return Vector4(
    glow.x + flare.x * intensity,
    glow.y + flare.y * intensity,
    glow.z + flare.z * intensity,
    1.0,
  );
}