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 contact = b.textures['contact_shadow_texture'];
  if (contact == null) return Vector4(1.0, 1.0, 1.0, 1.0);
  final center = contact.sample(v[0], v[1]);
  final surface = b.textures['surface_texture'];
  if (surface == null) return center;

  final centreDepth = surface.sample(v[0], v[1]).w;
  // The sky: the march wrote one here and there is no depth to weigh by.
  if (centreDepth <= 0.0) return center;

  final params = b.vec4('ContactShadowResolveInfo', 'params', Vector4.zero());
  final falloff = math.max(params.z, 1e-4) * math.max(centreDepth, 1e-3);

  final total = Vector4.zero();
  var weightSum = 0.0;
  // Offsets -2..+1 on both axes: every cell of the 4 x 4 pattern once.
  for (var y = -2; y <= 1; y++) {
    for (var x = -2; x <= 1; x++) {
      final u = v[0] + x * params.x;
      final w = v[1] + y * params.y;
      final depth = surface.sample(u, w).w;
      if (depth <= 0.0) continue;
      final weight = math.exp(-(depth - centreDepth).abs() / falloff);
      total.addScaled(contact.sample(u, w), weight);
      weightSum += weight;
    }
  }

  // The centre is always one of the taps and always weighs one.
  return total..scale(1.0 / math.max(weightSum, 1e-4));
}