run method

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

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

Implementation

@override
Vector4? run(Float32List v, ShaderBindings bindings, FragmentContext c) {
  final scene = bindings.textures['scene_texture'];
  if (scene == null) return Vector4(0.0, 0.0, 0.0, 1.0);
  final params = bindings.vec4(
    'LuminanceInfo',
    'params',
    Vector4(0.0, 0.0, -10.0, 1.0 / 16.0),
  );
  var sum = 0.0;
  for (var j = 0; j < 4; j++) {
    for (var i = 0; i < 4; i++) {
      final ox = ((i + 0.5) / 4.0 - 0.5) * params.x;
      final oy = ((j + 0.5) / 4.0 - 0.5) * params.y;
      final s = scene.sample(v[0] + ox, v[1] + oy);
      sum += 0.2126 * s.x + 0.7152 * s.y + 0.0722 * s.z;
    }
  }
  final mean = sum / 16.0;
  final stops = math.log(math.max(mean, 1e-6)) / math.ln2;
  final encoded = ((stops - params.z) * params.w).clamp(0.0, 1.0);
  return Vector4(encoded, encoded, encoded, 1.0);
}