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 fog = b.vec4('FogInfo', 'fog', Vector4.zero());
  // `TowardsEyeFrom`: to the eye, or against the view axis through an
  // orthographic lens — `P7`.
  final towards = towardsEyeFrom(b, v[4], v[5], v[6]);

  var facing = 1.0;
  if (towards.length2 > 0.0) {
    final n = Vector3(v[7], v[8], v[9]);
    final length = n.length;
    if (length > 0.0) {
      // `abs`, because nothing here is culled and a back face is as visible
      // as a front one.
      facing = (n.dot(towards) / length).abs();
    }
  }
  // Never to zero: a silhouette edge is exactly perpendicular to the eye, and
  // a face that vanished there would carve a dark seam along it.
  final intensity = 0.35 + 0.65 * facing;

  var fogged = 1.0;
  if (fog.w > 0.0) {
    fogged = math
        .exp(-fog.w * fogDistance(b, v[4], v[5], v[6]))
        .clamp(0.0, 1.0);
  }

  final scale = v[3] * intensity * fogged;
  return Vector4(v[0] * scale, v[1] * scale, v[2] * scale, 1.0);
}