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 velocity = b.textures['velocity_texture'];
  if (velocity == null) return Vector4(0.0, 0.0, 0.0, 1.0);
  final source = b.vec4('TileMaxInfo', 'source', Vector4.zero());
  final params = b.vec4('TileMaxInfo', 'params', Vector4.zero());
  final target = b.vec4('TileMaxInfo', 'target', Vector4.zero());

  final taps = (params.w + 0.5).floor();
  final tileX = (v[0] * target.x).floorToDouble();
  final tileY = (v[1] * target.y).floorToDouble();
  // `mix(1, taps, walk)`, per axis.
  final startX = tileX * (1.0 + (taps - 1.0) * source.z);
  final startY = tileY * (1.0 + (taps - 1.0) * source.w);

  var longest = Vector2.zero();
  var longestSpan = 0.0;
  for (var i = 0; i < 64 && i < taps; i++) {
    final at = velocity.sample(
      (startX + source.z * i + 0.5) * source.x,
      (startY + source.w * i + 0.5) * source.y,
    );
    final motion = _halfMotion(at.x, at.y, params, params.z);
    final span = motion.dot(motion);
    if (span > longestSpan) {
      longest = motion;
      longestSpan = span;
    }
  }
  return Vector4(longest.x, longest.y, 0.0, 1.0);
}