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 surface = bindings.textures['surface_texture'];
  if (surface == null) return Vector4.zero();
  final block = bindings.vec4('DepthPyramidInfo', 'block', Vector4.zero());
  final range = bindings.vec4('DepthPyramidInfo', 'range', Vector4.zero());
  final tapsX = (block.z - 1e-3).ceilToDouble().clamp(1.0, 32.0).toInt();
  final tapsY = (block.w - 1e-3).ceilToDouble().clamp(1.0, 32.0).toInt();
  final cornerU = v[0] - 0.5 * block.x;
  final cornerV = v[1] - 0.5 * block.y;
  final stepU = block.x / tapsX;
  final stepV = block.y / tapsY;

  var farthest = 0.0;
  var nearest = 3.0e38;
  var empty = false;
  for (var j = 0; j < tapsY; j++) {
    for (var i = 0; i < tapsX; i++) {
      final depth = surface
          .sample(cornerU + (i + 0.5) * stepU, cornerV + (j + 0.5) * stepV)
          .w;
      if (!(depth > 0.0)) empty = true;
      if (depth > farthest) farthest = depth;
      if (depth < nearest) nearest = depth;
    }
  }
  // The nearest depth as a fraction of the farthest, rounded down, in
  // alpha's upper half.
  final ratio = farthest > 0.0 ? (nearest / farthest).clamp(0.0, 1.0) : 0.0;
  final flatness = 128.0 + (ratio * 127.0 + 1e-3).floorToDouble();

  const steps = 16777215.0;
  final scaled = ((farthest * range.x).clamp(0.0, 1.0) * steps)
      .ceilToDouble();
  final high = (scaled / 65536.0).floorToDouble();
  final rest = scaled - high * 65536.0;
  final middle = (rest / 256.0).floorToDouble();
  final low = rest - middle * 256.0;
  return Vector4(
    high / 255.0,
    middle / 255.0,
    low / 255.0,
    empty ? 0.0 : flatness / 255.0,
  );
}