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 surfaceMap = b.textures['surface_texture'];
  if (surfaceMap == null) return _still;

  final u = v[0];
  final w = v[1];
  final surface = surfaceMap.sample(u, w);

  final inverse = b.mat4('CameraVelocityInfo', 'inverse_view_projection');
  final previous = b.mat4('CameraVelocityInfo', 'previous_view_projection');

  // The sky is at infinity: only the camera's turning moves it, so the
  // direction goes through last frame's matrix with w zero.
  final Vector4 then;
  if (surface.w <= 0.0) {
    final (origin: _, :along) = pixelRay(inverse, u, w);
    then = previous * Vector4(along.x, along.y, along.z, 0.0);
  } else {
    final eye4 = b.vec4('CameraVelocityInfo', 'camera', Vector4.zero());
    final forward4 = b.vec4('CameraVelocityInfo', 'forward', Vector4.zero());
    final world = worldAtDepth(
      inverse,
      Vector3(eye4.x, eye4.y, eye4.z),
      Vector3(forward4.x, forward4.y, forward4.z),
      u,
      w,
      surface.w,
    );
    then = previous * Vector4(world.x, world.y, world.z, 1.0);
  }

  // Behind last frame's eye: nothing to reproject from.
  if (then.w <= 0.0) return _still;
  final thenU = then.x / then.w * 0.5 + 0.5;
  final thenV = 0.5 - then.y / then.w * 0.5;
  return Vector4(u - thenU, w - thenV, 0.0, 1.0);
}