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 texture = b.textures['particle_texture'];
  var texel = Vector4(1, 1, 1, 1);
  if (texture != null) {
    // The larger of the two directions per axis. A hardware sampler uses the
    // longer side of the whole footprint parallelogram; taking the maximum of
    // the axis-aligned components is the same thing for a quad facing the
    // camera, which every billboard is by construction.
    var du = 0.0;
    var dv = 0.0;
    final ddx = c.ddx;
    final ddy = c.ddy;
    if (ddx != null && ddy != null) {
      du = math.max(ddx[4].abs(), ddy[4].abs());
      dv = math.max(ddx[5].abs(), ddy[5].abs());
    }
    texel = texture.sample(v[4], v[5], du: du, dv: dv);
  }

  var fogged = 1.0;
  final fog = b.vec4('FogInfo', 'fog', Vector4.zero());
  if (fog.w > 0.0) {
    final d = fogDistance(b, v[6], v[7], v[8]);
    fogged = math.exp(-fog.w * d).clamp(0.0, 1.0);
  }

  // The texture's alpha is coverage and the particle's is brightness, so the
  // two multiply.
  final scale =
      v[3] *
      texel.w *
      fogged *
      (soft ? softParticleFade(b, c, v[6], v[7], v[8]) : 1.0);
  return Vector4(
    v[0] * texel.x * scale,
    v[1] * texel.y * scale,
    v[2] * texel.z * scale,
    1.0,
  );
}